Energy Conservation In Housing, first half of book, Text Only (No Graphics copied on this web-site)

[Energy Conservation in Housing]

ENERGY
CONSERVATION
IN
HOUSING

A Collection of Data on
Energy-Efficient Housing Approaches

David L. Meinert

++++++++++++++++
NOTE: This Google “blog” did NOT put any of the drawings / graphics
necessary to
understand a lot of the information.
However, I have the complete (PDF) and Word documents of the text and
graphics
on this site. Go to “Home” of this site, and look at “Files” which
lists the book text in PDF format, as well as additional files on
other insulation and energy saving topics.

I also have the complete (PDF) documents of the text and graphics
on a Yahoo web-site.
The Yahoo site includes some photos of an attic and basement
insulation project. Use this link to connect to it.
http://groups.yahoo.com/group/EnergyConservationHousing
(Expect to have to sign in to the Yahoo group to access the data.)
Starting in November 2008, this data has been available on a different
site (“Multiply.com”).
http://energyconshousing.multiply.com/
The main improvement on this Multiply site is the ability to add
videos. I added some insulation videos that can be viewed on the
Multiply site. The Word and PDF documents are also on this site.
However, my home computer has been unable to open those documents on
the Multiply site due to some problem with “JavaScript.” If you run
into similar problems, the best source for the complete PDF and Word
documents is on the above Yahoo site.
Expect to have to “sign-in” to the Multiply site to access the data.
Previously the text Word and PDF documents on the Multiply.com site
were on an MSN site. http://www.msnusers.com/EnergyConservationInHousing
The MSN sites was closed in February 2009.
++++++++++++++++




The printed version was published by Vantage Press New York / Los
Angeles
in 1990 and re-printed in 1992. As of 1996, it was out of print.
This electronic version was re-edited in 2003








The following is the narrative that was printed on the back cover of
the original book, published in 1990 and re-printed in 1992.

$13.95

ENERGY CONSERVATION
IN HOUSING
A Collection of Data on Energy-Efficient
Housing Approaches

By David L. Meinert

In these days of soaring energy costs, it is the rare person indeed
who has not given some thought to how he or she can make this one
necessity of life more affordable. Once one has done the obvious –
keep the temperature down, not leave appliances on needlessly, et
cetera – what then? Prevention – that is, design of housing to
accommodate energy efficiency – is the answer. “But isn’t that
expensive?” you might ask. As David L. Meinert asserts in Energy
Conservation in Housing, it will be more expensive not to seek ways of
making your home more energy-efficient.
This book demonstrates in layman’s terms the principles of energy-
efficient housing so that you can get the most for your energy dollar
by designing and constructing a house using these principles or
modifying your current home. Basic types of heat loss and gain and
types of insulation, approaches for optimum energy efficiency in
building design, and ways to improve the supply of fresh air in
tightly constructed energy-efficient homes are the main topics
addressed. The many diagrams included and lengthy list of resources
will assist the reader in exploring energy conservation further.

About the Author

David L. Meinert, born in Quincy, Illinois, is a clinical optometrist
who accumulated his knowledge of energy conservation as a result of
several years of independent study. He is a graduate of Rock Valley
College, Northern Illinois University, and the Illinois College of
Optometry and is a former Army Optometrist.
Dr. Meinert currently resides in Herndon, Virginia, with his wife,
Lora.

Vantage Press, Inc.
516 West 34th Street, New York, N.Y. 10001

(The publisher no longer has any copies of the actual printed book.
It has been out of print since 1996.)







All persons making use of the information contained herein are
reminded that this information is intended to provide guidelines.
While much effort have been made to ensure this information is
accurate, the author makes no representation and gives no warranty
that this information, if used, will provide the energy savings
described. Much of this information is based on data from the
original 1990 and 1992 printings. Only some of the data has been
updated since then. The author assumes no responsibility whatsoever
for any loss or damage resulting from the use of any of this
information.
In a sense, this text can never be completely “finished” since
knowledge is always changing and expanding. (Certainly my time is
limited as to how many topics I can continue to research and update.)
However, the technology for insulation and ventilation is probably
over 90% complete at this time, so there is much to be gained by
understanding and utilizing the data in this text.






Copyright 1990 by David L. Meinert
Printed in 1990. Re-printed in 1992.
Original Published Text Printed by
Vantage Press, Inc.
516 West 34th Street,
New York, New York 10001

Original Published Text
Manufactured in the United States of America
ISBN: 0-533-08331-1

This book is out of print as of 1996.

Contents


Introduction . . . . . . . . . . . . . . . .
vi

Acknowledgments . . . . . . . . . . . . . . .
vii
Technical conditions or problems with this electronic
version . . . viii

Part One. Energy Fundamentals: The Road to
Understanding Energy-Efficient Housing
Insulation and Energy
Efficiency . . . . . . . . . . .
1
Basic Information on Heat Loss and
Gain . . . . . . . . . 1
Vapor
Barriers . . . . . . . . . . . . . . . . .
6
Window Orientation and Energy
Efficiency . . . . . . . . 9
Radiant
Barriers . . . . . . . . . . . . . . . .
16
Infiltration of Outside
Air . . . . . . . . . . . . .
19
Development of Energy-Efficient
Homes . . . . . . . . . 22
Analysis of Energy-Efficient
Homes . . . . . . . . . . . 23

Part Two. Superinsulation: The Energy-Efficient Solution
Why
Superinsulation? . . . . . . . . . . . . . .
29
Resolving Vapor Barrier and Insulation
Problems . . . . . . 29
Heat Loss
Calculations . . . . . . . . . . . . . .
35
Shape of the Building and Heat Loss and
Gain . . . . . . . . 42
Thermal Mass and the Drop of
Temperature . . . . . . . . 43
Heating
System . . . . . . . . . . . . . . . . .
44
Cooling Tubes for Summer
Cooling? . . . . . . . . . . 48
How Much Insulation Is Actually
Needed? . . . . . . . . 51
Heating Costs for the
Year . . . . . . . . . . . . .
54
Applications of Energy Technology to New
Homes . . . . . . 58
Retrofitting Insulation in Existing
Homes . . . . . . . . 74

Part Three. House Ventilation:
Fresh Air for Tightly Constructed Homes
Evaluating Air-to-Air Heat
Exchangers . . . . . . . . . . 82
Summary of Data on Commercially Available Heat
Exchangers . . . 88
Air-to-Air Heat Exchangers: List of Selected Commercial Companies
91
Air-to-Air Heat Exchangers: Homemade
Models . . . . . . . 96



Part Four. Additional Data on Energy-Efficient Housing
Comparative Costs of
Insulation . . . . . . . . . . .
111
Assembling Superinsulated
Walls . . . . . . . . . . . 115
Vapor Permeability of
Materials . . . . . . . . . . .
116
Selecting the Appropriate Overhang for South
Windows . . . . 119
Design Temperatures for Heating and Cooling for Selected Locations
122
Percentage of Sunshine for Selected
Locations . . . . . . . 124
Ground Temperatures in Shallow
Wells . . . . . . . . . 125
Magnetic Variations from True
North . . . . . . . . . 126
Winter Solar Gain and Deviation from
South . . . . . . . 126
Solar
Position . . . . . . . . . . . . . . . .
127
Clear-day Solar Gain for Double-glazed
Windows . . . . . 128
Moisture Condensation within Sealed Panes of
Glass . . . . . 129
Other Energy-saving
Ideas . . . . . . . . . . . . .
132

References . . . . . . . . . . . . . . . . .
135
Related
References . . . . . . . . . . . . . .
138
House Construction
Information . . . . . . . . . . . 139
Manufacturers and Product
Suppliers . . . . . . . . . 140

Index . . . . . . . . . . . . . . . . . . .
145
Appendix:
Retrofitting basement
insulation . . . . . . . . . . 147
Getting started on retrofitting and existing
home . . . . . 150
Practical data on retrofitting basement floor
insulation . . . . 151
Observations on vapor barrier
effectiveness . . . . . . 152
Attic radiant
barrier . . . . . . . . . . . . .
152
Air-to-air heat exchanger – Update
information . . . . . . 153




Introduction


This book is a collection of data on energy-efficient housing from a
wide variety of sources. It is intended to provide an overview to
help the reader gain knowledge and a better understanding of how to
reduce energy costs in housing.
Around 1980 I became interested in learning more about energy
conservation in housing construction when I was looking at designs of
homes. Since then I have collected data from a variety of sources on
energy-efficient housing as a hobby in my spare time. Most of this
book is a compilation of data I had obtained from 1980 through 1990.
While much of this data is “old” it still has substantial practical
applications. Although my usual occupation is unrelated to the topics
in this book, I found most of the data on energy-efficient housing can
be understood and utilized without prior training and experience.
Energy-efficient houses need not be complicated or unusually
expensive. When properly designed, they can serve to cut costs of
heating by 90 percent compared to energy use prior to 1970. A
properly designed energy-efficient house uses only about one-third of
the heat in winter as compared to houses with normal levels of
insulation. The energy savings in summer will also have significantly
reduced cooling costs.
I have tried to condense pertinent data from many sources. With this
information it is possible to gain a good understanding of energy
conservation and to apply these concepts in the design and
construction of future homes and the modification of some existing
homes.
Part One explains basic concepts in heat loss and gain and the types
and forms of insulation. Part Two explains approaches for optimum
energy efficiency in building design. Part Three explores ways to
improve the supply of fresh air in tightly constructed energy-
efficient homes. Part Four contains additional data to help the
reader better utilize energy efficiency principles. The references
list the many sources of this book and related topics for readers who
desire further information. Listed after the references are
manufacturers of some products described in this book. The last 7
pages (the Appendix) include additional practical details on home
insulation.







Acknowledgments

This book was produced by a compilation from many sources. Every
effort was made to give credit to the original source of the
information. Since these data were collected for many years, I am not
certain of the exact source of all pieces of data. Some of the data
were obtained from friends and experiences over the years.
The listed references will help the reader to gain more detailed
information on topics presented here. During the past twenty-five
years much work has been done to better understand how to conserve our
world's energy reserves and at the same time to make energy costs in
homes more affordable. Much credit is due the energy consultants,
home designers, and previous authors who have discovered and presented
this information in earlier publications.
I owe special thanks to William A. Shurcliff and Ed McGrath for
technical advice and helpful discussion on some of the topics covered
in this book. I am especially appreciative to Elise W. Mackie for
extensive editing contributions prior to submission of this text for
publishing.
This book was originally produced (around 1988) at home through the
capabilities provided by the Macintosh™ 512K Enhanced home computer,
by Apple ® and was printed on the Apple Laserwriter ™ to produce
camera-ready copies for the published pages. The published book was
out of print as of 1996.
The initial documents to produce this book were created on the
Macintosh (text by MacWrite program and diagrams by FullPaint
program). In 2002, I converted these documents into Word on the
Macintosh, then using the MacDrive 2000 program, was able to convert
the documents into Word 97, readable by Windows 98 computer systems.
I continued with editing work on the text and diagrams in 2003.

Technical conditions (or problems) with this electronic version.

The first procedure you should do is to make a back-up copy of this
text. It’s only about 4 MB, so it won’t take up much space on your
hard drive. If you have the capability, next time you back-up your
hard drive documents to a CD-R, save a copy of this document on the
CD.

Symbols. The main symbol I use in the text is “Delta” – used
typically for “change” as in “change of Temperature” or “Delta
T” (∆T). Delta is a triangular-shaped symbol (∆). That is how it
displays on my Window 98 PC. However, on my old Windows 95 laptop,
the Delta symbol comes out as a “square” shape, instead. If I then
open that document on the Windows 98 PC, the “Delta” symbol displays
as a triangle, which is the usual Delta shape.

Are there any blank pages? When I formatted this document, I selected
“page break” from the “insert” menu (I selected “break” then clicked
“page break” and “OK”) where I wanted the pages to end. This makes
the page numbers correspond to the Table of Contents and Index.
Depending on how your PC formats the pages, that spacing might be
off. You could end up with “blank” pages, and then none of the page
numbers would agree with the Table of Contents and Index. That would
then require a lot of work “re-formatting” either the text font
(typically I used “Times New Roman” font) or you could change the
margins, under “page setup.” Since it is electronic, you can find
what you want by using “Find” under the “Edit” menu.

Are columns of data out of alignment? Depending on how your computer
formats the text you could end up with data in some columns that are
out of alignment, due the tab settings and font size interacting
differently than how I formatted the columns.

Are there any problems visualizing the diagrams? Of the numerous
diagrams within the text, some are whole-page diagrams and others are
smaller. There is typically a short delay before the actual diagram
displays (even though the text around it immediately displays). I
have had occasions where a previously present diagram is “missing”
from the page. I then click where the diagram should be, and a
rectangular frame appears where the diagram should be, but still no
diagram. I then “double-click” in that rectangular frame, and a
“picture” is now displayed in a full-size “window.” This display is
only the picture, no longer the regular text version of the diagram.
Simply “close” this window, by clicking the second square (with an “x”
in it) at the upper right corner of the screen. The picture /
“object” should now appear in a rectangular place on the screen, where
it was initially missing. If that doesn’t work, then go to your “back-
up” copy of the document, go to that same position in the text. When
you see the correct diagram, highlight it (put the cursor on the
diagram, and press the left mouse button), then copy it (press the two
keys “Ctrl” and “c” – or select “Copy” from the “Edit” menu). Then
return to the original document with the missing diagram, highlight
it, press “backspace” then paste the replacement diagram in that
position (press the two keys “Ctrl” and “v” – or select “Paste” from
the “Edit” menu). Then “save” the document.
If the diagram shape / size gets distorted, it is possible to “reset”
the diagram. Select the diagram (put the cursor on the diagram and
press the left mouse button). Under the Format menu, select “Object,”
then select the “Size” tab, then click “Reset” and “OK.”


Part One
ENERGY FUNDAMENTALS
The Road to Understanding
Energy-Efficient Housing
Insulation and Energy Efficiency

Since the oil embargo of 1973, increased emphasis has been placed on
energy savings. Although the crisis is considered behind us, the
amount of available energy is not unlimited. With the rising price of
energy, more efforts have been made to conserve energy use for heating
and cooling buildings. While it is possible to enhance the energy
efficiency of existing buildings, it is easier to incorporate energy
saving techniques in new construction.
Insulating walls and ceilings is a well-known approach to conserving
heating and cooling costs of a home. Most houses built prior to the
early 1970s usually did not have insulation in the walls and had only
a small amount of insulation in the attic.
Today most housing codes mandate minimum levels of insulation
required in walls, ceilings, and floors for new construction.
Buildings insulated to current standards of construction provide
significant energy savings compared to most older buildings.
By incorporating current energy conservation knowledge into housing
design it is possible to build homes that require little conventional
heating. A highly efficient home can be economically heated during
winter in some of the coldest climates of the United States and
Canada. Such highly energy-efficient homes have even greater value
when energy prices rise; as fuel prices increase, heating costs for
poorly-insulated houses might increase by hundreds of dollars while an
energy-efficient house might have increased heating bills by only one-
tenth as much.

Basic Information on Heat Loss and Gain

Heat flows from warm objects to colder objects. The flow of energy
is measured in British thermal units, or BTUs. One BTU is the energy
required to heat one pound of water by one degree Fahrenheit. The
rate of heat flow depends on two factors: the temperature difference
(∆T) and the resistance to heat flow (R-value). Materials of high R-
values retard the flow of heat better than materials with low R-
values. 1
Various parts of a building have different rates of heat loss. By
adding insulation heat loss is slowed down, but not stopped. The
overall heat loss from a surface is measured by its heat transmission
(the "U-factor") or, more commonly, by its overall resistance to heat
flow (the "R-value"). The R-value and U-factor are inversely related.
1

These formulas demonstrate the relationship between the U-factor, the
R-factor, and the rate of heat loss from a surface.

U = 1 for a surface
R
Heat loss ( in BTU/hr) = U x Area ( in square feet) x ∆T
( in degrees Fahrenheit)

∆T (or "Delta Tee") = Inside to outside temperature difference
(°F.)

An uninsulated wall (R-4) loses heat more than three times faster
than a wall with standard levels of insulation (R-13). A
superinsulated wall (R-40) loses heat three times slower than a
standard insulated wall.
There is a tenfold reduction of energy loss from an uninsulated wall
(construction prior to 1970) to a superinsulated wall today. The
purposes of making a home well insulated are to reduce heat loss, save
energy costs, and make the building more comfortable.

Types of insulation

Fiberglass and rock wool (R-3 to 3.5 per inch). These mineral wool
insulations are made from the raw materials sand, glass, slag, and
stone. They are the most commonly used insulations. Fiberglass is
available in rolls, batts, loose fill, and rigid boards, with or
without a vapor barrier. Fiberglass and rock wool are fire-resistant
and moisture-resistant. They are irritating to skin, eyes, and lungs;
thus proper protection should be used during installation. 1, 2
Cellulose (R-3.8 to 4.2 per inch). This is shredded paper, treated
to be fire-retardant. Cellulose is an excellent insulator. Available
as loose fill. 1
Vermiculite and perlite (R-2.3 to 2.7 per inch). These are pellets of
light, expanded mineral material. Perlite and vermiculite are cheap
and easy to use, but with problems of moisture retention and
settlement. Available as loose fill. 1
Polystyrene. This is foam made from expanded plastic. Polystyrenes
are usually sold as rigid boards: beadboard (R-4) and Styrofoam
(R-5). Polystyrenes are reasonably moisture-resistant. Since these
foam products are flammable, they must be covered with a fire-
resistant substance, such as wallboard. Styrofoam typically has a
small amount of freon in its matrix, raising its insulative value
higher than that of beadboard. Beadboard is also termed expanded
polystyrene since beads of the expanded plastic are fused together.
Styrofoam is termed extruded polystyrene; it is tightly formed into
its final shape and results in greater strength than beadboard.
Freon is typically used in the manufacturing of most foam products.
Chloro- and fluoro-carbons, such as freon, cause damage to the ozone
layer of the atmosphere. Unlike the fluorocarbons used in extruded
polystyrene, expanded polystyrene releases the hydrocarbon, pentane,
during its manufacturing and curing process.
As of 2003, several versions of polystyrene are now available that do
NOT use or release volatile organic compounds (such as pentane) or
chloro- or fluoro-carbons (such as freon). (I found sources for CFC-
Free polystyrene by an Internet search using the words: polystyrene
insulation cfc-free.)

Isocyanurate and urethane (Thermax, R-Max [R-7 to 9, per inch]).
This is another form of foam insulation. Isocyanurate and urethane
are very effective insulating materials. They are moisture-resistant
and highly flammable, requiring a fire-resistant covering.
Isocyanurate and urethane foams have freon trapped within the foam
matrix. Since freon conducts heat less well than air, these foams are
better insulators. 2 With aging, the freon escapes, losing up to 20%
of its insulative ability in the first year. While the initial
insulative value per inch can be up to R-9, eventually the
isocyanurate and urethane foams may reduce to R-5.
Phenolic foam insulation (R-8.3 per inch). This is a type of closed
cell foam from chemical polymers. The foam reportedly does not lose R-
value over time, yet has about the highest R-value available. It is
quite fire-resistant and supposedly can even serve as a firewall. 3
Over time, due to water absorption, phenolic boards have apparently
caused cases of severe metal corrosion in roofing. Also, over time
this board was found to have significant shrinkage, reducing its
effective insulative ability. 43
Reflective foil (R-2.4 to 4.4 per surface). When facing an air space
of three-quarters of an inch or more, reflective foil is rated at
R-4.4 when reflecting down, R-2.4 when reflecting up, and R-3 when
reflecting horizontally. Reflective foil acts as a "radiant barrier"
to reflect back the heat waves of far-infrared thermal radiation.
Reflective insulation is of value in keeping such heat waves inside
homes in winter and may have greater value in keeping heat radiation
out of homes during hot weather. 4
Foam-in-place insulation is injected into closed wall cavities to
insulate previously uninsulated walls; it includes the following
types:
Urea formaldehyde (R-4.5 per inch): This foam was suspected of
producing dangerous formaldehyde gases and was banned in 1982 by the
U.S. Consumer Product Safety Commission. The ban is now lifted, but
urea formaldehyde is no longer a popular insulation. Urea
formaldehyde is flammable.
Tripolymer® foam (R-4.8 per inch) is a phenolic foam injected into
closed wall cavities, but does not have the gas emission problems of
the urea formaldehyde foams. It has significant vapor permeability
(perm of 15) thus needs a vapor barrier for protection from household
moisture. Tripolymer foam is fire-resistant.
Air Krete (R-3.9 per inch) is a foam that is composed of concrete and
air (95% air, thus no heavier than other blow-in or foam insulation).
Since it is made from concrete, it has extreme fire-resistance. 5
Urethane foam (R-7.7). Urethane expands excessively when foamed in
place and can rupture cavity walls. It also shrinks somewhat as it
cures. Urethane is flammable.

Forms of insulation

Rolls. These are blankets of insulation previously cut by the
manufacturer to specific thickness and width and sold in a rolled up
bundle. The width is made to fit between 16 or 24 inch stud spacing
(e.g. One size of roll insulation expands to 6 inch thickness. It is
23 inches wide, and 40 feet long). The insulation is cut to the
length needed by the installer.




Batts. These are insulation blankets that are cut by the manufacturer
to the usually needed lengths as well. Typically, five batts may be
sold in a rolled up bundle. Each batt has a specific dimension (e.g.
3.5" x 15" x 92") so as to fit in the space between studs. Such a size
would be used when the 2 x 4 wall is framed with studs spaced every 16
inches, with a final ceiling height of 8 feet. The installer needs
only to unroll the batt, put in place in the framed cavity, and staple
in position (with no cutting needed except for irregular spaces).
Loose fill. This insulation is composed of small particles or shreds
of insulation either poured or blown into open cavities. There may be
some tendency for the loose fill to settle. The machines for blowing
the insulation in place will break up the compressed insulation, fluff
it, and then blow it through a hose to the desired location. Loose
fill fiberglass and rock wool may cost slightly less for the same
volume of insulation than in rolls or in batts. Blowing insulation
works best with two installers, one to feed the blowing machine and
one to direct the hose around in the attic. Free use of a blowing
machine is often provided after purchase of a quantity of loose fill
insulation. Loose fill has some advantages in that it can fill in
irregular spaces with no additional work. Roll or batt insulation
must be cut for irregular shapes. Most blow-in insulations tend to
settle over time. A special adhesive (Blow-in Blanket®) can be mixed
with blow-in insulation to cause it to bind together. This prevents
later settling. 5 Blow-in Blanket is designed for use in retrofitting
insulation into existing walls.
Rigid boards. These are used for insulating basement or foundation
walls, as a layer within walls or roofs, or used as external sheathing
in new construction.
Reflective foil. Radiant barriers come in many forms: 1) foil bonded
to Kraft paper (single- or double-sided foil covering); 2) foil bonded
to polyethylene bubble sheets (single-sided foil or double-sided foil,
with single or double plastic bubble packs between the foil); 3) foil
bonded to asphalt material; 4) foil bonded to a polypropylene web;
and 5) foil covering sheathing board. Perforated foil allows water
vapor transmission, while still blocking radiant heat. Other forms of
radiant barriers are also available. Foil is bonded to other
materials because it is too fragile alone, unless it is made thick
(and thereby more expensive). Since a radiant barrier blocks radiant
heat, its effective insulative value is significantly higher than its
"R-4.4" rating under conditions of heavy solar radiation. Reflective
foil bonded to bubble sheets has a high insulative value (up to R-14,
reflecting downward).
Foam-in-place. Useful for filling in irregular spaces or for
insulating inaccessible areas or enclosed spaces. Foaming is a tricky
process and uses expensive equipment. Some of the foams have been
implicated in producing toxic vapors, resulting in severe indoor air
contamination. Before having a house foamed, the consumer should
investigate the specific manufacturer's product.


Insulation Summary

Raw Forms R-Value
Insulator material available per inch Problems

Fiberglass Glass Blankets 3.0 - 3.5 Absorbs water
Sand Batts
Loose fill
Boards

Rock wool Slag Blankets 3.0 - 3.5 Absorbs water
Rock Batts
Loose fill

Cellulose Paper Loose fill 3.8 to 4.2 Absorbs water

Vermiculite Mineral Loose fill 2.3 to 2.7 Absorbs water
Perlite

Styrofoam Petroleum Boards 5 Flammable

Beadboard Petroleum Boards 4 Flammable

Isocyanurate Petroleum Boards 5 to 9 Flammable,
Urethane emits cyanide gas
when burning

Phenolic foam Chemical Boards 8.3 Availability, shrinkage;
polymer due to water absorption,
it can rust adjacent metal

Reflective foil Aluminum Rolls Reflects radiant Fragile,
Sheets heat, R-2.4 or needs
more for one protection
surface

Urea- Chemical Cavity fill, 4.5 Gaseous emissions,
Formaldehyde polymer squirted into wall flammable,
spaces (resembles shrinkage,
shaving cream special equipment
until it sets)

Air Krete Cement, Cavity fill, 3.9 Special equipment,
air pumped into wall availability
spaces

Tripolymer Chemical Cavity fill, 4.8 Special equipment,
foam polymer squirted into wall availability
(phenolic foam, spaces (resembles
fire-resistant) shaving cream
until it sets)

Blow-in Blanket Special Blown into wall 4.1 Special equipment,
adhesive, after being mixed availability
loose fill with insulation
insulation

Vapor Barriers

What are vapor barriers, what are they for, and how do they function?

Vapor barriers are membranes or films used to prevent the movement of
water vapor from one side of the membrane to the other side. They
serve to keep moisture out of insulation and out of walls, floors, and
ceilings. Adding insulation without a vapor barrier (or putting the
vapor barrier on the wrong side of the wall) can damage the frame of
the house seriously.
Why is this? Just as heat flows from a warm place to a cool place,
so also vapor flows from where there is more vapor to where there is
less. Warm air can hold more water vapor than cool air. The inside
air of the house has more moisture in winter that the outside air.
The inside moisture tries to move to the outside. The moisture
travels through all materials porous to vapors. It travels through
the wallboard into the wall. As the vapor passes through the wall,
it reaches colder temperatures. Some of the moisture condenses on the
cold surfaces within the wall and freezes during the winter.
Insulation can hold the moisture in place all year, since walls have
little ventilation. Over the years the wall studs and siding can rot,
slowly destroying the building. Attics can escape the severe
consequences of condensation and thawing if there is adequate
ventilation. If not, the ceiling can be damaged from condensed water
running throughout the attic. Furthermore, insulation loses much of
its heat-retaining ability when wet and will slump and degrade if it
gets wet enough.
To prevent such condensation disasters, vapor barriers are used on
the warm side of the wall. That means that the vapor barrier should
be closest to the living areas of the internal home.

Inside relative humidity and vapor barriers

It is common that older homes use a humidifier in winter to add
moisture to the air. Homes equipped with a vapor barrier do not have
an air dryness problem; rather, the home tends to get too humid during
winter. The vapor barrier prevents the moisture from passively
diffusing into the wall. The vapor barrier protects the insulation,
protects the wall, reduces air infiltration, reduces heating costs,
eliminates the need for a humidifier, and may make it necessary to
remove moisture in winter instead of adding it.

Types of vapor barriers

Roll and batt insulation can be obtained with or without a vapor
barrier. Vapor barriers (when sold attached to insulation) have a
paper- or foil-coated facing with a tar-like material (i.e., asphalt)
under the paper. These vapor barriers usually slow down the
penetration of moisture enough to protect the insulation. To be
properly effective, the vapor barrier seams should be overlapping and
taped at the joints so that the moisture will not penetrate into the
wood framing and wet the framing or insulation.






A better approach is to have a continuous plastic membrane covering
the inside of the living areas. All joints of the plastic membrane
(vapor barrier) should be sealed. However, there will be far fewer
joints to seal with a continuous film (10 feet by 50 feet in size, or
larger) than there would be with all the individual vapor barriers
from each insulation batt. The typical vapor barrier material is 6
mil polyethylene, a plastic film that is 0.006 inches thick. Visqueen
is one brand of polyethylene. The 6 mil thickness is reasonably
sturdy and should withstand some abuse during installation. To
provide a smooth surface for attachment of the wallboard, the
insulation batts are typically stapled to the inside face of the studs
and only the polyethylene vapor barrier covers the stud surface to
which the wallboard is attached.
A vapor barrier can be made by sealing the edges of foil-covered
sheathing boards. Reasonable vapor barriers can be formed by use of
certain paints on the internal wall surface that significantly reduce
moisture penetration (e.g., Glidden "insulaid"). In new construction
a continuous polyethylene vapor barrier, applied prior to putting up
the wallboard, is preferable.





Limitations of vapor barriers

It is difficult to make a vapor barrier perfect. However, if the
vapor barrier is installed properly, it will protect the framing and
insulation from moisture and the damage it can cause. A properly
installed continuous vapor barrier will also block nearly all leakage
of outdoor air into the house, greatly reducing the space heating
demand for the house. However, even with a carefully applied vapor
barrier, there will be some moisture penetration through nail holes
and small tears. As occupants of the home hang pictures and mount
recessed lighting fixtures there will be new breaks in the vapor
barrier.
Vapor barrier tests from Sweden show that polyethylene can become
brittle and crack in as little as five years. Ultraviolet (UV) light
causes polyethylene to degrade. Thicker polyethylene is more
resistant to UV degradation, and reportedly black polyethylene is more
resistant to UV degradation than clear polyethylene. A thin layer of
polyethylene can degrade in as little as one year when exposed to
direct sunlight. Polyethylene degradation primarily occurs while the
material is exposed to sunlight during construction. After
construction, the polyethylene is safely within the wall and protected
from direct exposure.

Loss of vapor barrier integrity causes significant problems, since the
vapor barrier is needed for the life of the house. A polymer vapor
barrier has been developed in Sweden that resists degradation (TenoArm
® film) and is expected to last for the life of the house. 3 TenoArm
film is 8 mil thick and uses higher-quality raw materials with added
ingredients to stop degradation. It is slightly thicker than the
polyethylene conventionally used in house construction. See the
product information section after the references for more information.

Vapor problems with external insulative sheathing

A problem can occur when a standard wall is made with insulation and
vapor barrier and then external insulative sheathing is applied.
Often the insulative sheathing is foil-backed or polyethylene-coated,
making an excellent vapor barrier on the cold side of the wall. The
proper position for a vapor barrier is on the warm side of the wall.
Furthermore, some foam boards perform reasonably as a vapor barrier.
If the inside vapor barrier is not sealed substantially better than
the outside sheathing, there will be significant condensation over
time, wetting the insulation and rotting the wall. Since there is
little ability to ventilate an enclosed wall, it is important to
either have the external sheathing and siding vapor-permeable or have
sufficient gaps for the vapor to pass through the exterior of the
wall. There are some types of vapor-permeable foam insulation boards
that are designed to prevent condensation within the wall. An open
cell foam board, faced with perforated radiant barriers, will not
induce condensation if properly installed.

Window Orientation and Energy Efficiency

While much has been said about insulation in recent years, more can
be said of the significance of solar orientation of windows and the
resultant effect on the energy requirements of the building.
Windows serve to let in passive solar energy, dependent on their
orientation to the sun. Plenty of sun in winter can reduce the
heating bills of the building. Plenty of sun entering a home in
summer will tend to make the building less comfortable and will
significantly raise the cooling bill when air conditioning is used.
The key to controlling the sun's effect on home heating and cooling
costs due to windows is understanding how solar orientation of windows
results in solar gains for specific seasons and using that knowledge
to plan the layout of the building to optimize solar gain in winter
and minimize solar gain in summer. This is most easily done prior to
construction.


The sun's path in summer and winter.


The sun's altitude above the horizon is higher in summer. In winter,
the sun is low and to the southern sky. The change in the sun's
rising and setting direction causes east and west windows to get too
much direct sunlight in summer when the heat is not needed. South
windows get heat when needed (winter) and little heat when not needed
(summer). Redrawn from Home Energy for the Eighties, copyright by
Ralph Wolfe and Peter Clegg, published by Garden Way Publishing,
Pownal, VT 05261.

In winter the sun rises in the southeast, travels across the southern
sky, and sets in the southwest. Windows facing south will capture the
winter sun nearly the whole day and provide passive heating of the
building. East and west windows receive less than 50% of the solar
heat in winter compared to south windows. North windows receive no
direct sunlight in winter. Flat roof windows gain a small amount of
solar energy in winter.
In summer the sun rises in the northeast, travels nearly overhead,
and sets in the northwest. South windows receive very little direct
sunlight in summer. A properly sized overhang can prevent all direct
summer solar gain from south windows. North windows receive a small
amount of morning and evening sunlight in summer, but that heat gain
is relatively slight.
East and west windows receive their greatest solar gain in the heat
of the summer. East windows receive full solar exposure most of the
morning, and west windows receive full solar exposure most of the
afternoon. Even a very wide overhang would not completely shield the
east and west windows from the summer sun. External awnings or
external louvers are necessary to block a significant amount of the
solar gain from east and west windows in summer. Although internal
shading of east and west windows has some value in reflecting heat,
most of the unwanted solar gain has already gotten inside of the
building. Aluminum foil or other highly reflective films attached
directly to a window can block nearly all of the solar gain, but will
make the window significantly darkened or unusable for outside
viewing. Roof windows have their greatest gain in summer. Sloping
south windows also have substantial solar gain in summer.


Solar gain and loss through windows



Clear-day solar gain for windows of various orientations at 40° north
latitude. Gain and loss curves are calculated for double-pane windows
in various months of the year. The heat loss curve is representative
of 6,300 degree-days for Denver, Colorado. The net gain is the
difference between the gain and loss curves. South-facing windows
provide solar heat in proportion to seasonal heat demands. Other
window orientations provide more solar heat in seasons when it is not
needed. Statistical data are derived from Designing and Building a
Solar House and The Passive Solar Energy Book. Graph format is from
the Solar Energy Handbook.

For south windows to receive the full amount of winter exposure to
the sun, the south side should be free of obstructions, such as
buildings and trees that block solar gain. Even the branches of
deciduous trees could block excessive amounts of needed solar gain for
south windows during winter. A properly designed overhang shades
south windows in summer, while allowing full solar gain in winter.
Trees on the east and west are beneficial in providing summer
shading.

Summary: South-facing windows gain heat when needed (winter) and gain
little when not needed (summer). North windows have little gains year
round. East, west, and flat roof windows gain only a small amount of
sunlight in winter and gain a lot of solar heat when not needed in
summer. Gain from sloping south windows is actually dependent on the
angle of tilt. When facing closer to vertical, the gain is similar to
typical south windows; when facing closer to horizontal, they provide
less winter gain.



Most climates in the United States need heat in winter and should
avoid gaining heat in summer. South windows provide passive solar
heat when needed and avoid it when not needed. In a climate requiring
summer air conditioning, the objective is avoidance of the summer
sun. This means minimizing east, west, and roof windows as well as
skylights. In place of skylights it is possible to install vertical
windows high in the wall or ceiling (clerestory windows),6 preferably
facing south. These overhead windows will provide a better balance
of natural lighting without the summer solar gains associated with
roof or sloping windows. By opening clerestory windows during warm
weather, the homeowner allows the warmest air to passively leave the
home, drawing in cooler air from other windows. A fan mounted in a
clerestory window, actively exhausting the hottest air, could take the
place of a ceiling mounted whole-house exhaust fan.




How much is enough? (south-facing windows)

Since south-facing windows provide heat when needed (winter) and
provide little heat when not needed (summer), the more south windows a
building has, the better . . . . correct? Not quite so . . . .
Large amounts of sunlight can pass through windows. Additionally,
there is significant heat loss through windows. Single-pane windows
(R-0.89) lose 14 times as much heat as the same size of normally
insulated wall (R-13). Double-pane windows (R-1.84) lose seven times
as much heat as a normally insulated wall (e.g., 14 square feet of
double-glazed window area loses as much heat as 100 square feet of
wall area). Even triple-pane glass (R-2.79) loses almost five times
as much heat as a normally insulated wall. When compared to a
superinsulated wall (R-40), windows become a major cause of heat loss
for a building.

If there is a large amount of south-facing glass, the solar gain on a
clear winter day can cause the inside building temperatures to rise
uncomfortably high; the interior will quickly get cold as night
descends. A large amount of window space results in large daily
temperature fluctuations.
South-facing glass area should not exceed 6 to 8% of the total living
area in an energy-efficient home or overheating problems can occur if
special precautions are not taken.6 A home of 2,000 square feet size
should have a maximum of 120 to 160 square feet of south windows.

Window insulation

A single pane of glass has significant heat loss when the inside to
outside temperature difference is great. It would seem a simple
matter to add additional layers of glass to get extra insulative
value. A second pane of glass reduces the heat loss about 50% by
adding an insulating air space. Triple-pane glass has only one-third
the heat loss of single-pane glass.
Each layer of glass reflects or absorbs about 14% of the solar energy
striking it. Therefore, a single-pane transmits about 86% of
sunlight. Double-pane glass transmits about 74% and triple-pane glass
transmits about 64% of the solar energy reaching the outer pane of
glass. The advantage of adding more layers of glass has a point of
limited benefits; the additional panes of glass save more heat, yet
they cost more to install and block some of the solar radiation.
Movable insulation placed over windows during cold nights reduces
heat loss while allowing maximum heat gain during daylight hours.
Langdon 7 analyzed heat loss and gain through windows in various
winter climates and found the following:
1. Triple-pane is better than either double- or single-pane glass in
very cold climates for all window orientations.
2. In milder climates, south-facing windows perform slightly better
with double-pane than triple-pane glass, although all other window
orientations are usually better with triple-pane glass.
3. Using window insulation (R-5 or more) at night, double-pane
performs similar to, or slightly better than, triple-pane for south
windows. For all other orientations it is usually better to have
triple-pane with movable insulation.
4. Using window insulation during cold nights improves thermal
performance of all the windows types analyzed.

To be effective, the insulation must be put in place after dark and
removed in the morning. Due to cost and labor of installation as well
as the daily handling needed, window insulation is typically omitted.


Window-framing materials

In recent years, double-pane windows have become fairly standard in
new construction. Double-glazing is mandated by many building codes.
While double-glazing cuts window heat loss in half, the material
holding the panes in place is also quite important when considering
the insulative value of the window.
Wood, rigid vinyl, and fiberglass framing conduct heat at nearly the
same rate. Metals (e.g. steel and aluminum) conduct heat one thousand
times faster than wood or vinyl. 8 A wood or vinyl window frame
conducts heat less readily than the glass it supports. Metal frames
of windows will conduct heat many times faster than the glass they
support. For this reason, metal window frames not having an internal
thermal break will condense water vapor at a very low inside relative
humidity. From the inside of the house these metal frame windows
will seem to be nearly at outside temperatures. In winter this can be
like having a piece of ice sitting inside your windowsill.
Careful designing and more expense are required for metal windows to
be made with an internal thermal break. The thermal break occurs by
attaching the external aluminum frame to a nonconductive material
(e.g., wood or plastic) and the other side of the window frame
continuing with metal or wood framing. A metal frame having a thermal
break does not insulate quite as well as a nonconductive frame.
Another way of having a thermal break is attaching an exterior metal
storm window to a nonconductive window frame.

Number of windowpanes and inside condensation

Assuming that the window frame is less conductive than the glass,
i.e. wood, vinyl, fiberglass, or metal frame with a thermal break,
condensation will occur on the inside windowpane before the frame.
This condensation will occur at a specific level of inside relative
humidity.
Condensation on inside pane of glass. Since the additional air spaces
in multiple-pane windows add insulation, the inside pane of glass
stays warmer and condensation on its surface does not occur until
higher inside relative humidity levels. Window condensation occurs on
the inside pane of glass at the below listed percent (%) inside
relative humidity (RH) level for various types of windows (single-,
double-, triple-, and quadruple-pane glass). The temperature of the
inside pane of glass in degrees Fahrenheit (°F) is listed with the
percentage of relative humidity (% RH). A colder temperature of
inside glass means inside moisture will condense at a lower percentage
of relative humidity. The inside house temperature is seventy degrees
Fahrenheit (+70° F.) in all examples.



Table derived from The Superinsulated House, by Ed McGrath.

Triple-pane windows do not insulate well compared to a normally
insulated wall. However, they do allow the building to have a
reasonable level of inside relative humidity at very low outside
temperatures without causing unnecessary condensation on the windows.

Multiple-pane window designs

In older homes, double-glazing took the form of storm windows that
were put on in winter. Newer storm windows are attached directly to
the framing of the original window. The new storm windows can often
seal better than the older (inside) windows they cover. Any moisture
that leaks around the inside window stands a chance of condensing
between the two panes, since the moisture gets trapped there. For
this reason, weep holes are sometimes placed low in the storm window
frame to allow any condensed moisture to leak out.
Manufactured double-glazed windows are made with two panes of glass
sealed together in a frame separated by an insulating air space; there
is no ventilation between the panes. Manufacturers will often put
desiccant crystals in the spacer bars between the two panes of glass
to absorb moisture that gets around the inside pane. If the window is
subjected to excessive humidity levels and the inside pane develops a
poor seal, condensation will eventually occur between the panes.
Homemade window designs should seal the inside pane as perfectly as
possible; the panes external to the inside pane should be vented to
the outside to prevent any water vapor from condensing between the
panes. 2

Smart windows and smarter windows

Special treatment in the manufacturing of windows can reduce heat
loss. Coatings used in low emittance windows reduce heat loss by
reflecting heat waves back inside the house that would otherwise
radiate outside. Additionally, the coatings reflect away excessive
heat in summer. The low-E windows apparently reduce heat loss by 50%.

In the late 1980s a clear glass material was designed that offered
more than three times the insulating value of low-E glass. The
material called Aerugel provided more insulating value in one inch
(R-20) than a six-inch fiberglass batt (R-19). Aerugel was made of
silicon dioxide (found in sand) similar to ordinary glass. Aerugel
obtained its superior insulating ability by trapping air molecules in
microscopic spaces within its matrix. Aerugel is actually a
microscopic skeleton of silica (5% of its volume), the remaining 95%
of the space of Aerugel is trapped air.
The manufacturer (Quantum Optics Company, Emeryville, California) had
planned to make windows with a half-inch plate of Aerugel between two
panes of glass. This would have an R-10 insulation value and will be
almost as clear as triple-pane glass. 9 (Author’s note in 2003:
Aerugel has apparently never been added to the market for window
insulation. So Aerugel is only a theoretical type of window
insulation.)

Radiant Barriers

Heat loss or gain happens in three ways: convection, conduction, and
radiation. Convection occurs by the movement of heat contained in
moving fluids; that is, moving air or moving liquids transfer heat as
they flow from one position to another. Convective heat losses from a
building are stopped by windows, walls, ceilings, insulation, and
infiltration barriers. Conduction is the transfer of heat from one
object to another by direct contact of the two objects. Conductive
heat losses are blocked by reducing framing conduction between the
inside and outside surfaces and by sandwiching insulation between
framing layers. Dead air spaces in insulation will slow down
conduction and convection. Radiant heat travels through open spaces
and through many materials as infrared thermal radiation. Radiant
barriers serve a valuable function in reflecting away unwanted
radiant heat in hot climates. A radiant barrier is a reflective
metallic film, usually aluminum foil on a backing material. The
barrier has two features: high reflection and low emission of radiant
heat. With radiant heat blocked, a building has lower cooling costs
and becomes much more comfortable for the occupants. Radiant barriers
also reduce heat loss in winter. Eighty percent of radiant heat passes
through most building materials and ordinary insulation. A single
layer of a reflective barrier blocks 95% of the radiant heat striking
it. Additional layers of radiant barriers block only the 5% that
passes through the first barrier. Radiant heat gain and loss make up
a significant proportion of total cooling and heating demands.
Current research indicates that in open, uninsulated spaces radiating
heat is responsible for over 60% of the heat transfer. Convection and
conduction account for the balance of the heat transferred. When
insulation and a vapor barrier are used, heat conduction and
convection are minimized. A properly installed radiant barrier blocks
most of the radiant heat. A vapor barrier, a radiant barrier, and the
proper level of insulation block heat transfer optimally. Foil must
reflect into an air space to function as a radiant barrier. Without
an air space, the foil will conduct heat to other surfaces and not
serve as a barrier. The proper sized air space for a reflective
barrier is at least three-quarters of an inch.




In a study of ceiling solar gain in summer, a radiant barrier
combined with R-11 insulation performed thermally as well as R-30
insulation, during peak sunlight hours. Similarly, R-19 with a
radiant barrier gained less than half the heat compared to R-19 alone,
during peak sunlight hours. 10 For summer use, radiant barriers make
their biggest thermal contribution during times of high solar
radiation and less contribution after sunset. Since radiant barriers
are far less expensive than such comparable amounts of insulation,
they become an economical means of reducing heat gain in summer.
Radiant barriers can be installed in attics, in walls, and in floors
over crawl spaces.
Most radiant barriers are also good vapor barriers. To prevent
moisture condensation, such barriers should be installed in a position
suitable for a vapor barrier (when used in insulated spaces). A
perforated radiant barrier allows moisture to escape. In new
construction, the radiant barrier can be draped over the top chord of
the roof trusses before applying the plywood sheathing or attached to
the underside of the top chord. In the draping technique, the foil is
made to sag between the rafters to supply the needed reflective air
space. Radiant heat passing through the roof is stopped by the
barrier. Radiant heat warms the air space above the foil. The
accumulated heat leaves the attic through ridge vents and gable vents
in the attic. Retrofitting radiant barriers can be done by attachment
to the underside of the roof rafter. Reportedly, dust covering a
radiant barrier reduces its insulative value somewhat. For this
reason, double-sided foil has advantages: initially both sides of the
radiant barrier function fully. The side facing up reflects away
radiant heat; the layer facing down does not emit heat. Over time,
the layer facing up loses effectiveness as dust covers it. The layer
facing down continues to function fully.

A radiant barrier beneath the roofing material will raise the roofing
temperature a few degrees. It is believed that this temperature
increase will accelerate the aging of roofing material. One roofing
manufacturer contends that installing a radiant barrier effectively
voids the warranty on their roofing material. By using plentiful
attic ventilation above the radiant barrier, overheating of the
roofing material can be minimized. Provide continuous soffit vents
and use ridge and gable vents to insure proper ventilation.



Cautions on radiant barrier sales

Radiant barrier companies market products that have up to six layers
of foil, spaced to fill 2x6 inch or 2x4 inch framing cavities. They
claim superior insulating properties over standard insulation and
absence of the moisture damage properties of standard insulation.
Some companies appear to indicate that standard insulation is not
usually needed with proper use of foil layers.
Since a radiant barrier blocks 95% of radiant heat, leaving only 5%
of the radiant heat to be stopped by additional layers, what purpose
are the other five layers serving? Mainly they function as dead air
spaces to slow down heat conduction. This is precisely what standard
insulation does more effectively. Installed in the space provided by
a 2x6 inch ceiling joist, six layers of foil are rated by its
manufacturer 11 as R-12 for heat flow up and R-24.2 for heat flow
down. One layer of foil is rated by the same manufacturer as R-3.4
for heatflow up and R-12.4 for heatflow down. An R-19 insulation batt
filling the 2x6 inch space, combined with one layer of foil, results
in R-22.4 for heat flow up and R-31.4 for heat flow down.
Substituting the five additional foil layers instead of standard
insulation is less effective; batt insulation provides a much better
series of dead air spaces than five layers of foil. A single layer
radiant barrier blocks 95% of heat radiation; the conventional
insulation slows heat convection and conduction. Effective thermal
performance occurs if one radiant barrier is combined with the needed
amount of conventional insulation.
Much confusion surrounds the current knowledge of radiant barriers.
It may take years before the facts of radiant heat are known. In the
meantime, the buyer should be cautious.


Infiltration of Outside Air

In many houses there is a significant amount of leakage of outside
air. The outdoor air leaks into the house through any crack or
crevice of the wall, floor, or ceiling or the air passes directly
through porous wall sections. This leakage of outside air into a
building is referred to as infiltration. When driven by even mild
winds (fifteen miles per hour), a conventional home can undergo one to
four complete changes of air in one hour.1 Infiltration makes a house
feel drafty and uncomfortable in winter and significantly increases
the heating bill, since heated air is forced out with infiltration.
Exfiltration is the term describing heated air forced out of a
building.
By contrast, a well sealed home can undergo one air change in two
hours (one-half air change per hour). With the use of a continuous
vapor barrier surrounding the living area and properly sealed doors
and windows there can be less than one air change every 12 to 24 hours
(less than 0.1 air changes per hour).
In the early years of energy efficient buildings, reduction of
infiltration and improvement of the level of insulation made homes far
more economical to heat. Before long it was found that there were
side effects of having a home extremely well sealed. The first
effect, obvious within hours, is the tendency for water vapor to
collect inside the home. High water vapor content in the air can be
suspected when moisture condenses on double-pane windows. Other side
effects occur over time as the occupants breathe contaminants and
germs trapped in stale inside air.
Such indoor air pollution is typically worse than outdoor air
quality. The pollution can come from a variety of sources: carbon
monoxide from incomplete combustion of stoves or heaters, carbon
monoxide and other by-products from smokers, chemicals emitted from
new building materials, excessive water vapors, radon from the soil
and some masonry building materials, and other miscellaneous
contaminants. Radon, a dangerous radioactive gas from uranium, can be
present in soil anywhere. As well as getting into some building
materials, it can enter homes through foundation cracks, porous
cement, sump pump drains, pipes entering the foundation, and well
water. A thoroughly ventilated crawl space below a well-sealed floor
eliminates most sources of radon entering the house. Radon is second
only to smoking as a cause of lung cancer. 12 If the degree of
infiltration is less than 0.25 to 0.5 air changes per hour, then the
building will tend to have a higher concentration of contaminants than
is healthy. Infiltration is the only source of fresh air in
conventional homes. Forceful winds cause fast rates of infiltration;
minimal winds result in too little infiltration. Therefore,
infiltration is not a reliable way to get a consistent supply of fresh
air even in conventional homes. Infiltration with conventional homes
is related to the speed of the wind, not to the amount of contaminated
air.
It is necessary to have a good vapor barrier to keep moisture from
condensing inside the insulation of walls, floors, and ceilings. A
properly installed vapor barrier will block much of the infiltration.
It may then be necessary to ventilate the house to provide the needed
fresh air.


Ventilation

Ventilation means bringing fresh air into a building and exhausting
the stale air to the outdoors in a controlled fashion. Fresh air is
easily provided by opening windows, which increases the heating bill
and causes drafts in cold weather. Another approach is to bring
outside air in through the furnace cold air duct, allowing the air to
be heated on its way inside the house. Specific areas of the house
should be ventilated to remove moisture, odors, and contaminants.
Usually the kitchen, laundry room, and bathrooms should have air
exhausted to the outdoors. Exhaust fans have a difficult time
getting enough replacement air to vent adequately in a tight house.
Instead of opening a window to feed the exhaust fan, it is preferable
to provide the needed fresh air using a special type of whole-house
ventilator.

The air-to-air heat exchanger

A whole-house ventilation system provides fresh air while stale air
is exhausted. All exhaust air is vented to one point and fresh air is
brought in at another point. By bringing hot stale air in close
proximity to the incoming cold fresh air, it is possible to exchange
the heat between the two streams of air. In this way, the outgoing
air heats the incoming air. Since this heat is extracted from the
outgoing air, it is a way to get fresh air without having to heat the
air to reach room temperature. Such a device is known as a Heat
Recovery Ventilator (HRV) or perhaps more descriptively as an air-to-
air heat exchanger.



Having a slow rate of continuous ventilation will provide fresh air
as well as exhausting contaminants from the house. The efficiency of
the heat exchanger is a measure of its heat recovery capability. The
efficiency rating can range from 50% to 90% in models commercially
available. It is also possible to construct a homemade heat
exchanger, although it takes a significant amount of work. The
commercial exchangers tend to be somewhat expensive, although they pay
back the cost over time when compared to merely opening a window for
ventilation or having leaky doors or windows to allow infiltration. A
properly arranged vent plan for an air-to-air heat exchanger places
exhaust ducts in the bathrooms and kitchen while providing fresh air
ducts for all other rooms. This could eliminate the need for
individual bathroom and kitchen exhaust fans; the heat exchanger fans
remove contaminated air and supply fresh air. Another approach is to
route the exhaust fan ducts from the bathrooms and kitchen into an
exhaust air chamber, which then leads into exhaust chamber of the air-
to-air heat exchanger.

Air supply ducts can be made by use of inside wall, ceiling, and floor
cavities or by putting actual ducts through these spaces, depending on
requirements of the local building code. Initially it was felt that
supplying fresh air at one point in the house would allow even
ventilation. Although this may work for open floor plans, individual
rooms do not receive an adequate supply of fresh air.
It might seem a good idea to add the fresh air to the cold air inlet
of the forced air heating system. There are two problems with this:
1) The fan power of the furnace is much stronger than the heat
exchanger fans. This would cause a tremendous imbalance of the
airflow through the exchanger. 2) In an energy efficient home, the
forced air ventilation system runs so infrequently that it would not
adequately circulate ventilation air. Some heat exchanger companies
recommend turning the forced air fan to the "on" position whenever the
exchanger is operational so that fresh air from the heat exchanger is
properly distributed. This technique will suffice, but much
electricity is required for the frequent operation of the high-powered
furnace blower. In the long run, it is more cost-effective to install
fresh air ducts for the heat exchanger vent system instead of using
the ducts of the heating system to mix the fresh air within the
house.
If one retrofits a heat exchanger in an existing house, duct booster
fans mounted in the forced air heating system ducts could be used to
provide adequate mixing of the house air. Duct boosters have low power
consumption (e.g. 25 watts for 200 cubic feet per minute airflow); if
strategically placed in the heating ducts, two of these fans operating
continuously might provide adequate mixing of house air. The duct
boosters could maintain continual airflow throughout the house, mixing
the air without continual operation of the high-powered furnace
blower.

Infiltration barriers

There are a number of brands of housewraps designed to reduce
infiltration into houses. These infiltration barriers are thin
plastic sheets made from a fine pattern of polymer fibers. The tight
weave blocks air from blowing through the housewrap film, yet the
films are readily permeable to vapors, allowing any trapped moisture
to escape through the barrier. Tyvek ® was the first brand of
housewrap and has a perm of 94. With this high permeability, it
readily allows moisture to pass through.
Typically, the low-cost housewraps can be purchased in either a 3- or
9-foot width. With standard insulated walls, such housewraps cut heat
loss by 29% to 33%, as shown in independent laboratory tests using 2 x
4 inch frame walls with 3.5" (R-11) insulation in a 15 mile per hour
wind.14 The heat savings occur by blocking infiltration and by
keeping cold air out of the insulation, to maintain its full thermal
performance. Infiltration barriers are installed on the outside of the
wall between the sheathing and the siding. Vapor barriers are put on
the inside of the wall. If the vapor barrier is continuous, then
infiltration is not a problem. If a continuous vapor barrier is
provided, housewrap products still have a function by preventing cold
air from blowing into the insulation. The insulation retains its full
thermal value when covered exteriorly with a housewrap.
Commercially available housewraps are: 1) Tyvek; 2) Rufco-Wrap; 3)
Barricade Building Wrap; 4) Airtight-Wrap; 5) VersaWrap; and 6) Tu
Tuff Air Seal.15


Development of Energy-Efficient Homes

Over the years people have discovered that modifications of standard
insulation levels can cause dramatic savings in the energy costs of
keeping a home at comfortable temperatures. The thousands of dollars
spent achieving a special design can pay monthly dividends by reduced
energy costs. Such building types have been termed solar homes, earth
homes, envelope homes, and superinsulated homes. All incorporate
features to reduce the energy demands for heating and cooling. These
types of homes have outstanding thermal performance. Some owners of
these houses claim that they rarely need additional heat to keep the
house comfortable in winter, since the homes require only small
amounts of heat at specific times. The energy-saving houses have
advantages that justify slightly higher construction costs.
Earth homes reduce energy demands by having a substantial amount of
the house underground. The south side of the earth home is usually
exposed to the sunlight to take advantage of passive solar energy.
Since underground temperatures do not change as much as the outside
air temperature, the earth home can achieve a more stable internal
temperature. Insulation below ground is still required since the
earth is not as warm as needed for normal living conditions.
Solar homes seek to capture the energy of the sun by the passive
means of sun entering through windows or active means of solar
collector plates absorbing heat or converting sunlight to
electricity. Active collection is a complex and costly process.
Passive solar homes collect heat through properly placed windows; the
resulting heat of the sun is stored in the mass of the building.
The envelope home has been described as "a house within a house."
The envelope house is passive solar. It has some of the advantages of
an earth home since it is usually built partly into the ground. The
envelope home uses double walls on the south and north sides of the
house. A complete envelope of circulating air is present with
envelope homes since the attic space and the crawl space beneath the
home connect the air spaces in the north and south walls. As the sun
enters the south windows, it heats the air in that space. The heated
air automatically rises, traveling into the attic. The solar heat is
transferred to the mass of the internal house it surrounds. As the
air cools, it travels in the air space along the north wall. The path
of the air is completed by returning through the crawl space. The
south side of the house is usually made into a large sunspace, an
enclosed sun porch.
Superinsulated homes have a design of exterior walls, floor, and
ceiling to allow very little heat loss. South-facing windows provide
passive solar gains. The home does not need to be underground, nor
does it require a sunspace to function. Plans for superinsulated
houses usually incorporate an air-to-air heat exchanger.


Analysis of Energy-Efficient Homes

Energy efficient home types result in less utilization of space
heating either by decreased heat loss or by harvesting other available
energy. An obvious disadvantage of energy saving homes is the
additional expense of the planning and construction. Energy efficient
homes as well as many conventional new homes result in poor indoor air
quality. For this reason, extra ventilation must usually be added.

Earth-sheltered home

Earth-sheltered homes use the earth to moderate temperature extremes.
Outside air has seasonal changes in temperature from -30°F to over
+100°F in some areas of the United States. The ground near the
surface changes in a similar way to the air temperature. However, the
ground temperature seven feet below the surface of the earth stays
within a twenty degree range year-round throughout most of the United
States. In winter, the ground is warmer than the air; in summer, the
ground is cooler than the air. While the earth is not warm, it
certainly has less extreme temperature differences than above ground.
The exterior of earth homes is usually insulated to levels between
R-30 for parts of the home near the surface and R-10 for parts of the
house deepest in the ground.

Earth-sheltered home


The moderating effect of the surrounding earth decreases the heating
and cooling requirements to minimal levels. With most of the home
substantially underground, there is minimal heat loss in winter.
Since there is south-facing glass, the windows gain passive solar
heat.

The cooling effect of an earth home makes summer performance very
hard to match. In summer, the cooler surrounding earth will offset
the gains of heat from the air temperature. The cooling effect may be
partially due to the absence of radiant solar heat; solar radiation is
unable to pass through two feet or more of the earth covering the
home. The thick layer of soil absorbs the solar radiation so it
cannot reach the dwelling, making an earth home feel cooler than
conventional homes.
A good moisture seal on the outside of the building is very important
since all exterior surfaces could allow water to enter the home. The
walls and ceiling must be constructed much more solidly than in
conventional homes due to the massive weight of earth. Such homes are
impractical where the ground is very moist, having a high water table,
or very cold, such as where permafrost exists. Earth homes work best
when built into a south-facing slope, but can also be built on flat
land.

Solar home

Solar homes capture the heat of the sun by passive gains and/or by
active collection. Passive solar heat is transferred to the mass of
the house by the sun shining directly on heat absorbing masonry floors
and walls (e.g., Trombe Walls) and by having the passively heated air
circulate throughout the house by fans. Active solar systems absorb
the heat of the sun in specially designed collectors and transfer it
to a heat storage chamber (rock bin, water tank, or other storage
medium) or actively collect solar energy by photovoltaic cells.

Solar home




Instead of going through extreme means to reduce heat loss, solar
homes seek to collect the needed amount of solar energy and use it
from storage as required. Thermal mass is an important feature of
passively heated solar homes. The received sunlight is stored in
walls and floors capable of holding much heat. The heat-holding
capability of such masonry walls and floors prevents overheating
during the heat-up phases and allows a slow release of the heat during
times when sunlight is not plentiful.
Active solar systems are very expensive, requiring a very long time
before energy savings equal initial costs. Active solar homes require
a fairly large area of south-facing roof for solar collection and
sufficient inside space for storage of the heat.
Passive solar houses require extensive amounts of south-facing
glass. Heavy masonry surfaces are needed for thermal storage of the
collected solar energy. During prolonged periods of cold, the large
glass area loses considerable amounts of heat. The stored heat may
not be sufficient for the building needs because of rapid heat loss
through the large window areas. In the final analysis, when the
temperatures drop very low, thermal mass is not adequate.

Envelope home

Envelope homes entered the energy efficient housing market in the
late 1970s and the early 1980s. It is a home connected to the earth
by a circulating envelope of air. It is passive solar and passive
cooling and has no moving parts except for vents that are open or
closed depending on the season. The home performs thermally so well
that it quickly gained recognition for its energy savings. This
seemed to be the design for all sensible homes.
Why did the house perform so well? First of all, the house has two
sets of standard insulated walls on the north and south. The east and
west walls are well insulated or superinsulated. Both the ceiling and
the roof are insulated separately. The attic air plenum is insulated
from all sides. Twice the amount of insulation of a conventional
house is used. There is a moderating effect of the earth in the
crawl space below the house, providing some heat storage. There is
lavish use of windows on the south side. This solarium, or sunspace,
is a very attractive feature of the envelope house. The envelope home
is far beyond conventional houses in energy conservation.
There are still many strong advocates of envelope homes, yet the
popularity of these homes has declined somewhat over the years.
Enthusiastic owners are convinced that the houses have the best living
conditions possible, although they admit it has a higher cost than the
superinsulated design.



The envelope home is more labor-intensive to build than some other
types. The double north wall is difficult to construct. There is a
potential chimney effect: if a fire starts in the outer envelope, it
can be fed by a circulating stream of continuously available air.
There can be a significant problem in meeting some local fire codes.
Extra labor is necessary for insulating both sides of the air plenum
along the south walls, in the attic plenum, and in the north walls.
The house tends to collect stale air in the inner home. However, the
occupants can ventilate the inner house to the envelope for fresh air,
since the outer envelope often gets enough infiltration.



It is claimed that solar heat gained in winter is stored in the mass
of the house, but the opposite can be shown by calculation. The heat
enters the outer envelope, and due to the cold outdoor temperatures,
more of the heat escapes outdoors than is absorbed into the house. At
least two-thirds of the solar gain is lost before it has the chance to
be absorbed into the mass of the house. Metz suggested it would be
more efficient to have the sunspace connected with an insulated heat
storage chamber below the house and to eliminate the vast plenums
surrounding the house, with air circulated by a thermostatically
controlled fan.17 It would cost far less and function much more
effectively than the air envelope surrounding the house.
Shurcliff was also not convinced that envelope homes were the best
design.18 While the homes perform well, they are expensive to
construct and have potential fire problems with the air plenum and the
heat storage means are ineffective. Much of the received heat leaves
the structure through the vast expanses of glass used in the outer
south walls. He suggested that heat storage is far more effective
using other means. Shurcliff recommended that air circulation could
be accomplished more economically by use of fans and ducts instead of
by the large air plenums.


Claims were made for the superior insulating effect of the double
wall design (an inner R-11 wall and an outer R-19 wall). However,
when comparing that to a single superinsulated wall (of R-30 value),
the plenum space in between can be shown thermally to make no
significant difference.

Heat loss calculations for the attic of the envelope home during a
winter day. The outside temperature is 0° during the day and the
inside is 70°, attic temperatures are 100°, roof insulation R-19,
roof heat loss area of 1,450 square feet, ceiling insulation R-13,
ceiling area of 1,000 square feet. There is 100° ∆T (temperature
difference) from the attic plenum to outside (100° - 0° = 100°).
There is a 30° ∆T from the attic plenum to the inside of the house
(100° - 70° = 30°). The roof heat loss is 7,630 BTU/hr ( 1/19 x
1,450 sq ft x 100° ∆T = 7,631 BTU/hr). The heat lost through the
ceiling (transferred inside the house) is 2,300 BTU/hr ( 1/13 x 1,000
sq ft x 30° = 2,307 BTU/hr). In this above example: 7,630 BTUs
escaped outside, and only 2,300 BTUs were stored in the mass of the
house.

Superinsulated home

Superinsulated homes have as their main feature low heat loss. There
are no air plenums as found in the envelope house. There are no
active solar collectors. It's just a plain house from the outside and
the inside. It does not need to be built underground, with a
basement, or on a hillside.
The low heat loss results from unusually high levels of insulation.
When the heat loss from the house is slowed sufficiently, the house
performs very well thermally. However, the house is so well sealed
that it does not get adequate fresh air; it requires one-half day or
up to several days for one air change by infiltration. For this
reason, a fresh air ventilator (air-to-air heat exchanger) is
necessary for stale air to be exhausted and fresh air to be drawn in.
The heat exchanger transfers most of the heat of the outgoing stale
air to the incoming fresh air. McGrath describes five parts to a
superinsulated house: 1) Adequately insulated roof, wall, and floor
sections (termed fixed building sections), 2) the air-to-air heat
exchanger, 3) an arctic entryway, 4) shutters on the windows, and
5) an insulated door. 2 When questioned about the use of window
shutters, McGrath admitted that few superinsulated homes in Fairbanks,
Alaska, use shutters on the windows. The superinsulated design
reduces the heating requirements to such low levels that shutters are
not economically required even in those arctic climates.

The arctic entryway is merely a vestibule or mudroom, outside or
inside, sealed from the rest of the house. It allows people to enter
but prevents cold air from directly entering the house. In this way,
a person enters, closes the door, then goes through another door to
enter the rest of the house. Some analysts have argued that if there
is a good vapor barrier, the cold air will not blow far into the
house. Nonetheless, with a small entry room, the cold air that enters
the house can be limited significantly. This will increase the
comfort of the occupants and will cut down on cold drafts in winter.




Current knowledge suggests that superinsulation should have the
following features:
1. The proper level of continuous insulation in all exterior surfaces
of the building.
2. A continuous vapor barrier.
3. An air-to-air heat exchanger.
4. Proper solar orientation of the windows.
5. An arctic entryway.
6. A nearly continuous radiant barrier (it need not be sealed at
junctions to perform as a radiant barrier).




Part Two
SUPERINSULATION
The Energy-Efficient Solution

Why Superinsulation?

Of all the plans described, superinsulation is the simplest design,
requiring the smallest investment of materials to incorporate energy
saving features; superinsulated buildings can be built in virtually
any location. The design reduces heat loss and serves to recover heat
from all appliances used within the home. The normal amount of
windows is used, while allowing for enough south-facing windows to
contribute to the heating needs of the house. McGrath stated in his
book: "Advocates of superinsulated and passive solar houses have spent
time arguing with each other about which is better, but for my part, I
see no point in it: all superinsulated houses should be passive solar,
and all passive solar homes should be superinsulated." 2

Resolving Vapor Barrier
and Insulation Problems

Vapor barrier problems

A continuous vapor barrier is not present in most conventional
homes. Plumbing connections pierce the vapor barrier. Electrical
wiring and boxes pass through the vapor barrier and are not sealed.
Numerous other breaks are present in the vapor barrier in standard
construction. Even if all of these breaks in the vapor barrier are
sealed, new breaks are made by hanging pictures, mounting towel racks,
and installing recessed wall fixtures.

Insulation problems

Even if all the insulation is properly installed, the wood-framing
members will make up 15 to 25% of the wall area, depending on the
framing techniques utilized. While the insulation is R-11, the wall
studs have less insulating ability (R-5), lowering the final
insulative value of the R-13 wall to about R-10. This stud conduction
problem can be remedied by external insulative sheathing. Since the
inside vapor barrier is less than perfect in standard construction,
moisture accumulation in walls can result from the insulative
sheathing technique unless vapor permeable sheathing is used.



Crosshatch walls

A crosshatch wall helps maintain the vapor barrier integrity by
attaching the vapor barrier to the inside of the framed wall.
Horizontal cross members (2x2s or 2x4s) are attached to the vertical
studs. This reduces heat conduction through the wall and allows space
for electrical wiring without breaking the vapor barrier plane. The
crosshatching method is also known as strapping or cross strapping.19

Double walls

There are several different designs of double walls used to reduce
wall conduction. The methods of making double walls include the party
wall and several possible variations of double walls.
Stud conduction is a main source of heat loss through walls. Another
source of heat loss through walls is conduction through headers used
over doors and windows. A header is a framing member used above
windows and doors that is needed to support the weight of the roof or
floor above. Essentially the entire space within a header is filled
with the framing member itself. This leaves virtually no room for
insulating headers in standard framing. Use of double walls allows
the potential of dramatically reducing heat conduction through headers
as well as conduction through wall studs.




The double wall. Two parallel rows of 2x4 inch framed stud walls
allow for substantially more insulation to be utilized. Conduction of
the top and bottom plates is eliminated, as is stud conduction and
conduction through headers present over doors and windows.








The backward double wall is assembled nearly the same as a standard
platform framed house, except the floor joists should be cantilevered
to the position of the projected outside wall. The vapor barrier is
mounted between the sheathing and studs of the inner wall. Earlier
versions placed the vapor barrier on the outside of the inner wall.
However, Canadian research suggests that the vapor barrier could be
damaged more readily by wind loading. Also, exterior mounting of the
vapor barrier prolongs the exposure to UV light during construction
and increases the chance it will get damaged before the exterior wall
is completed. If the vapor barrier is mounted exterior to the
sheathing, it must be well fastened down (e.g., sealed and secured in
place by wood strips) to prevent it from detaching under windy
conditions.
The backward double wall allows space within the inner wall for the
electrical wiring, piping, recessed fixtures, and relative safety of
the vapor barrier from most internal home modifications. The
insulation is placed exterior to the inside wall. This allows the
vapor barrier to remain intact for the life of the house, since it is
well protected by the thickness of the inside wall. The backward
double wall can be made so that the inside wall, the outside wall, or
both walls are load-bearing.
The backward double wall has the best features to protect the vapor
barrier, reduce stud conduction, and provide as much space as needed
for the insulation to be used. The inside wall cavity does not
require insulation because the wall cavity external to it can hold all
the needed insulation. If 12 inches of insulation are used in the
wall (R-40 wall), the wall will have a total thickness of 16 inches
plus the external siding. The internal 3½ inches is taking up space
but not contributing either to inside space or to insulation.




Temperature gradients and the backward double wall

Wall temperatures drop progressively from the inside wall to the
outside of the building. Depending on the relative humidity of the
inside air, moisture could condense before reaching the vapor
barrier. With the air-to-air heat exchanger running continuously at
an adequate rate, sufficient moisture will be removed from the inside
of the house to drop the relative humidity to a safe level.
The inside wall can be used for additional insulation and not cause
condensation problems, as described by the superinsulators of Alaska
and Saskatchewan, Canada. At least two-thirds of the insulation
should be external to the vapor barrier (2:1 ratio) for moderately
cold climates that never get below 0° F. For colder climates it is
advisable to have a 3:1 or 4:1 ratio of outside to inside
insulation. With 12 inches of insulation external to the vapor
barrier and 3½ inches of insulation (all fiberglass) inside the vapor
barrier (3.4 : 1 ratio), there should be no condensation inside the
wall even if the outside temperature drops to -60° F (if less than
35% indoor relative humidity is maintained). The additional
insulation would increase the insulation properties of the R-40 wall
to R-50.









If moisture is not being removed from the house to keep it below the
proper relative humidity for the coldest conditions expected, there is
significant danger in using insulation on the warm side of the vapor
barrier. Condensation in the inner wall could rot the studs, causing
serious structural damage to the home.
For additional details on design and construction of superinsulated
wall types, also consult The Superinsulated Home Book, by Nisson and
Dutt. 41


Heat Loss Calculations

Standard guidelines for determining the size of a heating system
needed in a home do not apply to energy efficient houses. The heat
loss from energy efficient houses is so slight that conventional
systems overwhelm the heating needs. It is necessary to make some
preliminary calculations to determine the heating output needed to
keep the house comfortable in all conditions. Heat loss factors from
various surfaces as well as the energy needed to heat the ventilation
air are important considerations.

Heat loss / gain formulas:

Heat loss (BTU/hr) = U (heat transmission) x Area (sq ft) x ∆T (°F)
or
Heat loss (BTU/hr) = 1/R for the surface x Area (sq ft) x ∆T (°F)

Sample calculation I. For an uninsulated 2x4 inch frame wall (R-4),
with 100 square feet of wall area and an inside to outside temperature
difference of 70° (0° F outside and 70° inside = ∆T), the heat loss
can be calculated:

Heat loss = 1/4 x 100 sq ft x 70°
Heat loss = 1750 BTU/hr

Sample calculation II. For a standard 2x4 inch frame wall with
insulation (R-13), with 100 square feet of wall area, ∆T = 70°, the
heat loss can be calculated:

Heat loss = 1/13 x 100 sq ft x 70°
Heat loss = 538 BTU/hr

Sample calculation III. For a superinsulated wall, e.g., 12 inches of
insulation (R-40 for the wall), with 100 square feet of wall area, ∆T
= 70°, the heat loss can be calculated:

Heat loss = 1/40 x 100 sq ft x 70°
Heat loss = 175 BTU/hr

When the total heat loss of a building drops to a sufficiently low
level, the heat gained by the "living process" inside the home starts
to make up much of the remaining heating demands. Heat from the
living process, also termed internal gains, comes from heat given off
by people, lights, and appliances. These internal gains can provide
1500 to 3000 BTUs per hour to the heat requirements of a residential
home. Each kilowatt-hour (KWH) of electricity used in the home gives
off 3,410 BTUs.


Each person gives off heat, depending on the person's size and energy
expenditure (100 to 600 BTU/hr).2 The actual gains will vary with the
number of occupants, the energy usage of the occupants, and the actual
home appliances. Once the heat loss is very low, the internal gains
of the home will make up a significant percentage of the home heating
needs.

Heat loss calculations for five sample houses (winter)

The specifications of a house to be used for heat loss calculations
are: 28 feet by 44 feet in floor area, single story over a crawl
space, 8 foot ceiling, having 80 square feet of south-facing glass, 24
square feet of east-facing glass, and 40 square feet of north-facing
glass. There are two doors 20 square feet each. The nighttime
average temperature is calculated at -10° F (for 12 hours), and the
daytime average is +20° F (for 12 hours). The inside temperature is
kept at 70° F. Location is 40° north latitude (southern
Pennsylvania), with 50% sunshine during the month of January.
Calculations include internal gains of 1,500 BTU/hr.

Example 1. An underinsulated house (minimal ceiling insulation), with
spontaneous infiltration of 1.0 air change per hour and single-pane
windows.
Example 2. A normally insulated house with a spontaneous infiltration
rate of 0.5 air changes per hour and double-pane windows.
Example 3. A superinsulated house with ventilation controlled at 0.5
air changes per hour and triple-pane windows.
Example 4. A superinsulated house with an air-to-air heat exchanger
(75% efficient) providing ventilation of 0.5 air changes per hour, and
triple-pane windows.
Example 5. This house is identical to example 4, except that the owner
added on a sunspace having 100 square feet of south-facing standard
double-pane glass. The sunspace is separated from the house and
provides the home 50% of received solar heat by way of a
thermostatically activated fan.
Notes on sunspaces: See the solar gain tables, overhang tables, and
section on window orientation and energy efficiency to design the
optimum thermal performance of sunspaces. A sunspace with south-
facing windows can serve to collect solar heat for the home. However,
the large window area results in substantial heat loss in winter after
sunset; to prevent heat loss from the home, the sunspace should be
thermally separated from the house. A sunspace used for supplemental
heating should have mainly vertical south-facing windows and little
thermal mass (such as wooden walls and floors) to allow the
thermostatic fan to duct excess heat to the house. A sunspace used as
a greenhouse will need more thermal mass (concrete or brick walls and
floors) so the heat can be absorbed and retained in the greenhouse,
although not providing much additional heat for the house.

Source Example
1 2 3 4 5

Wall R-value 4 13 40 40 40
Ceiling R-value 6 19 50 50 50
Floor R-value 4 13 40 40 40
Window R-value 0.89 1.84 2.79 2.79 2.79
Door R-value 4 8 15 15 15
Window loss (BTU/°F/hr) 162 78 52 52 52
Walls + ceiling
+ floor loss (BTU/°F/hr) 755 234 80 80 80
Door loss (BTU/°F/hr) 10 5 3 3 3
Heat for ventilation
air (BTU/°F/hr) 177 88 88 22 22
Net heat loss
(BTU/°F/hr) 1,104 405 223 157 157
Heat loss/hr
@ -10°F (80° ∆T) 88,320 32,400 17,840 12,560 12,560
Heat lost/24 hrs (12h
@-10°; 12h @+20°) 1,722,240 631,800 347,880 244,920 244,920
Heat gain (solar) 67,164 57,762 49,674 49,674 81,511
Internal gains 36,000 36,000 36,000 36,000 36,000
Net heat
needed/day 1,619,076 538,038 262,206 159,246 127,409

Hours/day an 80,000 BTU furnace must run to maintain inside
temperatures of the
sample homes: 20.23 hrs 6.72 hrs 3.27 hrs 1.99 hrs 1.59 hrs

Calculations for heating ventilation air. Air volume per hour (cubic
feet/hr) x 0.018 BTU/cu ft/°F/hr (specific heat and density factor) =
BTU/hr needed to heat the air. If a heat exchanger is used, multiply
the result of this calculation by 0.25 (75% of the heat is recovered,
25% of the heat must be added). 28' x 44' x 8' (ceiling height) =
9,856 cubic feet, which is one air change for this sized house. 9,856
cu ft x 0.5 (when 0.5 air changes is the infiltration or ventilation
rate) = 4,928 cu ft/hr (or 82 cubic feet per minute as a ventilation
rate).
Wall calculations. 1152 sq ft of walls, less 40 sq ft of doors and
144 sq ft of windows, gives 968 sq ft x 1/R = heat loss/°F/hr for
walls.
Ceiling calculations. 1232 sq ft x 1/R = heat loss/°F/hr for ceilings
Floor calculations. 1232 sq ft x 1/R = heat loss/°F/hr for floors
Door calculations. 40 sq ft x 1/R = heat loss/°F/hr for doors
Window loss calculations. 144 sq ft x 1/R = heat loss for windows
Window gain calculations. Solar gain tables in part four of this book
are calculated for double-pane glass. Increase the calculated gains
for single-pane windows (in example 1, divide the gain for each window
by 0.86 to get the single-pane values). Reduce the calculated gains
for triple-pane windows (multiply the values by 0.86).
South window area (80 sq ft) x 0.90 (framing) x 0.50 (proportion of
sunny days) x 1415 BTU/sq ft/day January heat gain.

East window area (24 sq ft) x 0.90 (framing) x 0.50 (percent sunny) x
445 BTU/sq ft/day January heat gain.
North window area (40 sq ft) x 0.90 (framing) x 0.50 (percent sunny)
x 112 BTU/sq ft/day January heat gain.
Sunspace area (100 sq ft) x 0.90 (framing) X 0.50 (proportion of
sunny days) x 0.5 (proportion vented to home) x 1415 BTU/sq ft/day
January heat gain.



Summary of winter calculations

Uninsulated and underinsulated homes lose a substantial amount of
heat during cold winter days and nights. Solar gains and internal
gains make up only 6% of the heating needs.
Conventionally insulated homes require only 33% of the heat of the
underinsulated homes. The internal and solar gains now make up about
15% of the heating needs.
A superinsulated house would lose only 14% of the heat of an
underinsulated home. The internal and solar gains make up 35% of the
heating needs. The result is that the superinsulated home needs only
10% of the furnace heat when compared to an underinsulated home. The
superinsulated home needs only 30% of the furnace heat compared to
homes with conventional amounts of insulation.
The addition of a sunspace to the superinsulated home further reduces
the heating demands. The 127,400 BTU deficiency per day could be
supplied by occasional use of a fireplace, heat pump, or small
furnace.




Summer heat gain calculations

The same home specifications as for winter are used in calculating
the summer heat gain. For comparison, we will vary the amount of east/
west windows with the north/south windows of other examples. The
nighttime average temperature is calculated at 75° F (for 12 hours)
and the daytime average is 100° F (for 12 hours). The attic
temperatures, however rise higher, averaging 120° (for 12 hours). The
inside temperature is maintained at 75° F. Location is 40° north
latitude, with 85% sunshine during the month of July. Calculations
include internal gains of 1,500 BTU/hr.

Example 6. An underinsulated house (minimal ceiling insulation), with
spontaneous infiltration of 1.0 air change per hour. (Windows: 80 sq
ft South, 24 sq ft East, 40 sq ft North; all windows are single-pane.)
Example 7. A normally insulated house with a spontaneous infiltration
rate of 0.5 air changes per hour. (Windows: 80 sq ft South, 24 sq ft
East,40 sq ft North; all windows are double-pane.)
Example 8. A normally insulated house with window orientation
different from example 7. (Windows: 80 sq ft West, 24 sq ft North,
40 sq ft East. )
Example 9. A superinsulated house with an air-to-air heat exchanger
(75% efficient) providing ventilation of 0.5 air changes per hour.
(Windows have same orientation as example 8, above): 80 sq ft West, 24
sq ft North, 40 sq ft East; all windows are triple-pane.
Example 10. A superinsulated house with an air-to-air heat exchanger
(75% efficient) providing ventilation of 0.5 air changes per hour.
(Windows have same orientation as example 7, above): 80 sq ft South,
24 sq ft East, 40 sq ft North. all windows are triple-pane.)


Source Example
6 7 8 9 10

Wall R-value 4 13 13 40 40
Ceiling R-value 6 19 19 50 50
Floor R-value 4 13 13 40 40
Window R-value 0.89 1.84 1.84 2.79 2.79
Door R-value 4 8 8 15 15
Window gain
(BTU/°F/hr) 162 78 78 52 52
Walls + floor heat gain 550 170 170 55 55
Door gain 10 5 5 3 3
Cooling of ventilation
air (BTU/°F/hr) 177 88 88 22 22
Net heat gained
(BTU/°F/hr), less ceiling 899 341 341 132 132
Heat gain/hr, less ceiling
@ 100°F (25° ∆T) 22,475 8,525 8,525 3,300 3,300
Ceiling gain (BTU/°F/hr) 205 65 65 25 25
Ceiling gain (@ 120°)
(45° ∆T) BTU/hr 9,225 2,925 2,925 1,125 1,125
Heat gain/24 hrs (12h
@100°;12h @75°) 380,400 137,400 137,400 53,100 53,100
Heat gain (solar) 73,474 63,188 97,289 83,668 54,340
Internal gains 36,000 36,000 36,000 36,000 36,000
Net cooling
needed/day (BTU/day) 489,874 236,588 270,689 172,768 143,440

Hours/day a 30,000 BTU air conditioner must run to cool the house
16.33 hrs 7.88 hrs 9.02 hrs 5.75 hrs 4.78hrs

Window gain calculations. Increase the calculated gains for single-
pane windows. (In example 7, divide the double-pane values for each
window by 0.86 to get the single-pane values.) Reduce the calculated
gains for triple-pane windows (multiply the double-pane values by
0.86).
South window area x 0.90 (framing) x 0.85 (proportion of sunny days)
x 550 BTU/sq ft/day July heat gain.
East/west window area x 0.90 (framing) x 0.85 (percent sunny) x 985
BTU/sq ft/day July heat gain.
North window area x 0.90 (framing) x 0.85 (proportion of sunny days)
x 374 BTU/sq ft/day July heat gain.

Sunspace area. Although the earlier mentioned sunspace (example 5)
has gains in summer, the windows are opened for excess heat to go
outside. The thermostatic fan is turned off for the summer. The
sunspace is thermally separated from the house in summer, thus does
not increase the cooling demand.




Summary of summer calculations

Uninsulated and underinsulated homes gain a significant amount of
heat during hot summer days. Conventionally insulated homes require
about 48% of the cooling of underinsulated homes. Window orientation
is significant in summer also. A greater proportion of east and west
windows can easily make a home have 50% more summer solar gains than
when east/west windows are minimized. This increases the cooling load
and makes the home more uncomfortable, causing a 20% increased cooling
load in the superinsulated house. (Compare examples 9 and 10.)
Window factors being equal, superinsulation has 29% of the summer
cooling bills of an underinsulated house. The superinsulated house
has 61% of the cooling bills of a conventionally insulated house.
In summer, solar and internal gains add to the cooling load; in
winter, the solar and internal gains decrease the heating load.
Therefore, energy savings in summer are not so dramatic for
superinsulation as in cold winters, although increased insulation
levels will reduce cooling costs significantly.
Additional factors to be considered:
1. If south windows are provided a proper overhang, direct summer sun
is blocked, while the winter sun can still obtain full exposure. The
actual solar gains in summer would be less than half of the calculated
values for the south windows if a proper overhang is provided.
2. When the outside temperature is 100° F, the attic temperatures can
potentially be much higher than 120°, making greater depth of attic
insulation even more important in summer. A radiant barrier in the
attic can drop ceiling heat gain to far lower levels.
3. The air is often cooler near the floor than the ceiling. This
changes the heat loss/gain data, but was not calculated here.

Shape of the Building and Heat Loss and Gain

Since heat loss is related to surface area, the shape of the building
is an important factor. The more surface area, the faster the heat
loss. The smaller the surface area, the slower the heat loss, when
all other factors (such as insulation levels) are kept constant.
A sphere has the least surface area for a given volume. Using normal
building shapes, two-story buildings and square shapes lose less heat
than single-story buildings and long rectangular shapes when exterior
surfaces are equally insulated.

Example A. A single-story ranch house of 2,000 square feet living
area has 5,440 square feet of outer surface area. Assume 50 feet by
40 feet house dimensions, with 8 foot ceilings. (40 ft x 8 ft x 2
walls) + (50 ft x 8 ft x 2 walls) + 2,000 sq ft ceiling + 2,000 sq ft
floor = 5,440 sq ft surface area.
Example B. A two-story house with 1,000 square feet living area per
floor has 4,210 square feet of outer surface area. Assume 40 feet x
25 feet house dimensions with 17 feet combined height of the two walls
plus the floor between. (40 ft x 17 ft x 2 walls) + (25 ft x 17 ft x
2 walls) + 1,000 sq ft ceiling and 1,000 sq ft floor = 4,210 sq ft
of surface area. If the house shape is totally square for each floor,
the surface area is 4,150 square feet.
A two-floor design, still keeping the same total living area, has an
outer surface area of only 77.4% of its earlier amount. This means
heat loss from the outer surface is also reduced if insulation levels
in all exterior surfaces are kept the same. Changing from a one-story
to a two-story design can save space-heating energy.
Solar gain is related to the window orientation and size. The long
sides of the house facing north and south allow sufficient south-
facing windows. The optimum building shape is north and south sides
of the building 1.5 times longer than the east and west sides of the
building,6 e.g., if the east/west sides are 28 feet long, the north/
south sides of the building should be 42 feet long. This ratio
provides a suitable amount of space for placement of south windows,
with only a slight increase in building surface area.
The 2,000 square foot building in Example "A," would have 5,431
square feet of outer surface area for a square shape (44.7 x 44.7
ft). If the shape is changed to 37 ft x 55 ft (using the 1.5 ratio),
the outer surface area would be 5,472 square feet, only a slight
increase in surface area. The 1.5 ratio results in the area of the
south wall being 50% greater than the east or west wall, allowing for
placement of the necessary south-facing windows.
The two story 2,000 square feet building in example "B": a 26 ft x
39 ft floor size results in 4,210 square feet outer surface area. The
1.5 ratio results in a slight increase of surface area over a square
floor area (4,150 sq ft).
While decreasing external surface area of a building offers the
potential for decreased energy consumption, it does not guarantee it.
The actual insulation level in each section of a building is also a
very significant factor in the final energy used for space heating.


Thermal Mass and the Drop of Temperature

The total effect of insulation in a building determines the rate of
heat loss (BTU/hr). The speed by which temperature of the building
drops is determined by its heat-holding capability. This heat-holding
capability is referred to as the thermal mass of the building.
All materials hold a certain amount of heat depending on the specific
heat of the material and its density.

Properties of heat storage materials

Material Specific heat Density Heat capacity (BTU/cu ft/°F)
(BTU/lb/°F) (lb/cu ft) No voids 30% voids

Water 1.00 62 62 43
Scrap iron 0.12 490 59 41
Scrap aluminum 0.23 170 39 27
Concrete 0.23 140 32 22
Stone 0.21 170 36 25
Brick 0.20 140 28 20

Data obtained from New Energy Technology: Some Facts and Figures,
edited by Hottel and Howard. Published by MIT Press.

When basement walls are insulated exteriorly by foam boards, the
thermal mass of the concrete walls is within the building, serving to
store heat. The brick of a fireplace built within the insulated
enclosure is thermal mass within the building. However, it is common
that brick of fireplaces is continuous with the inside and outside,
resulting in much heat loss from the building. The uninsulated brick
does not function as thermal mass, since heat cannot be stored unless
insulation retains the thermal energy. An exterior brick façade
cannot function as thermal storage for the building. A brick wall as
an interior partition provides thermal storage.
Everything that is inside the building stores heat, all interior
walls, furniture, and appliances. A standard house can have 10,000
BTU storage capability without any planning for heat storage; for each
10,000 BTUs of heat lost, such a house loses 1° F. The uninsulated
house in example 1 (in winter), loses 88,320 BTU/hr for an outside
temperature of -10° F. The inside temperature would drop about 9° in
the first hour if no heat were added. The standard insulated house
loses 32,400 BTU/hr (example 2), and the temperature would drop about
3° in the first hour. The superinsulated house with the heat
exchanger loses 12,560 BTU/hr (example 4) and drops just over 1° F in
the first hour.


If special measures are taken to add thermal mass, the temperature
drop would be much slower. One way of adding thermal mass is by
having a small room in the basement filled with sealed water jugs.
One thousand gallons of water stored in the room would add about 8,600
BTU storage capability. Air circulating through the water storage
room would give off heat as the house needed it, slowing down the heat
loss of the house. The temperature of the superinsulated house
(12,560 BTU/hr loss, example 4) would drop about 7° over a 12-hour
period with the higher level of thermal mass. (12,560 BTU/hr x 12
hours, less 18,000 BTU internal gains in 12 hours gives 132,720 BTUs
lost in 12 hours [at -10°F]. Since there is now an 18,600 BTU storage
capability of the house, about 7° would be lost in the 12 hours
[132,720 BTU/hr ÷ 18,600 BTU/°F = 7.14°].) An overnight power/heat
failure would not be a crisis in a superinsulated house. However, an
uninsulated house would be below freezing by the morning. The true
heat loss would be fractionally smaller, since as the house loses
heat, the ∆T decreases, thereby slowing the heat loss slightly.

Heating System

Sizing it to the needs of your house

A forced air ventilation system is an advantage to have in a home
receiving plentiful solar gain. The ventilation system can be turned
to the "fan" setting during the day, allowing for the passively heated
air to be distributed so that the heat is stored evenly throughout the
mass of the house.6, 19 Alternatively, duct boosters properly placed
in the duct system could circulate the air at a lower electrical cost.
There is a large difference between the heat needs of the uninsulated
house (88,320 BTU/hr in example 1) and the superinsulated house
(12,560 BTU/hr in example 4). Conventional gas or oil-fired heating
systems are geared to provide enough heat for poorly insulated
houses. Such furnaces are often greater than 70,000 BTU/hr capacity.
Smaller sized furnaces are now available in the 20,000 to 40,000 BTU/
hr range, which would be suitable for superinsulated houses. (See
furnace manufacturer listings.)
Wood stoves and fireplace inserts also provide heat, often exceeding
the needs of well-insulated houses. Use of a wood stove requires a
brief time of combustion to raise the temperature of the home and then
a cool-down period until it is necessary to re-light the stove to
reheat the home. Wood stoves and fireplaces tend to have excessive
emissions; their use is restricted by legislation in some areas. The
emissions are reduced, dangerous creosote deposits in the chimney are
reduced by 90%, and additional heat is produced by use of a catalytic
element in the exhaust gas pathway. Catalytic units are available
with some wood stoves and fireplace inserts.
Electrical resistance heaters can supply a wide range of heat demands
and are quite affordable. Electrical resistance heat has been termed
100% efficient, all electricity being converted to heat.
Unfortunately, electrical heat is more expensive per BTU. Electricity
is often derived from burning of fossil fuels, which could directly
heat the home. As fuels are burned and electricity is produced and
delivered, about one-third of the energy from the fuel actually
reaches the home. Burning natural gas to run a generator to heat a
home with the electricity so generated requires up to three times as
much gas burned as gas burned in the house furnace. 2

Another way of using electricity to generate heat is use of a heat
pump. A conventional heat pump moves excess heat from the home in
summer and releases the heat outdoors. When the mode is reversed, the
unit extracts heat from cold outside air and brings the heat indoors
for winter use. Efficiency of the heat pump is highest when inside
and outside temperatures are fairly similar. Conventional heat pumps
can attain coefficients of performance (COP) of up to 5 or 6. For
every kilowatt put into powering the compressor motor, 5 or 6
kilowatts of heat energy are obtained. 2 Since a superinsulated
house usually does not need heat until the outside temperature is near
freezing, the coefficients of performance (COP) may not be as
favorable. Once the COP drops down to 1.0, efficiency is the same as
using electrical resistance heating; when outside temperatures drop to
+5° F, the COP is down to about 1.0. As long as the heat pump is
operating at an efficiency greater than 3, it is operating at the same
efficiency as if fuel producing the electricity were burned in the
home.
Considering the rate of heat loss from conventional homes, it would
take a high capacity heat pump to supply the heating needs of the
house when outside temperatures drop to +20°F. Since heat pump
efficiency is related to outdoor temperatures and winter causes high
heat demands, back up electrical resistance heat is typically provided
for heat pump operation. When the heat pump cannot supply the heat
demands, or if the efficiency drops too low, the back-up heat will
activate. Some heat pumps are designed to operate with a fuel (other
than electricity) for back-up heat; when the efficiency of the heat
pump drops to a certain level, the back-up fuel system will engage.
Another heating option is an oversized water heater used to supply
additional warmth for space heating, with heated water circulating
through coils into the forced air ventilation system of the house or
to a separate radiator unit. Water heater supplied space heating is
suitable only when powered by fuels less expensive than electricity.

Geo-thermal heat pumps

Another approach to heat pumps is a geo-thermal heat pump. The
outside part of the pump is a closed loop of water running underground
through polyethylene or polybutylene piping. From the ground the
water extracts heat in winter and coolness in summer. (The ground is
warmer than the air in winter and cooler than the air in summer.) For
cooling the geo-thermal heat pump can attain an EER efficiency rating
up to 15; for heating, it can have a COP as high as 3.98. 20 A geo-
thermal pump can also provide hot water instead of using a
conventional water heater. It is best to plan for a geo-thermal heat
pump in advance of construction. About 400 feet of 1.5-inch
polyethylene piping must be buried 4 to 6 feet in the ground to
provide heat exchange for each 12,000 BTU/hr ("one-ton") capacity. If
the heat exchange pipes are within several feet of other heat exchange
pipes, more pipe length will be needed (up to 670 feet per ton
capacity). With the low energy demands of a superinsulated house, a
one-ton capacity could suffice.




Geo-thermal heat pumps: Earth loop configurations
Adapted from: Manual of Acceptable Practices for Installation of
Residential
Earth-Coupled Heat Pump Systems by W.S. Fleming and Associates,
Inc.



For normally insulated homes, the usual methods are to:
1. Excavate an area of the yard to bury the piping.
2. Drill a deep well and insert a heat exchange tube.
3. Drill multiple shallow wells with exchange tubes, or
4. Bury the heat exchange pipes in the septic drainage field, if on-
site sewage disposal is used.

Superinsulated homes will typically require only one-third the
capacity of conventionally insulated homes. Alternatively, ground
water may be used as the heat or cooling source for a geo-thermal pump
by drilling wells, although it requires large volumes of water and may
go against local or federal codes to discharge water (or heated water,
in areas where thermal pollution is an ecological consideration).

For a superinsulated house, a geo-thermal heat pump makes more sense
than a standard air-source heat pump. A superinsulated house will
rarely need heat until the outside temperatures drop near freezing.
When the outside temperatures drop near freezing, a standard heat pump
has fairly low efficiency. Geo-thermal heat pumps rely on ground
temperatures for heat exchange; ground temperatures are typically much
warmer than outside air temperatures during the coldest times of
winter. A properly-sized geo-thermal heat pump will maintain good
efficiency throughout winter despite low outside air temperatures.
The addresses of geo-thermal heat pump manufacturers are listed after
the references.

Heating systems: Is too big always too big?

Texts on energy-efficient housing usually recommend heating systems
sized within 10% of the house heating demands. 6 A 20% oversized
system tends to lose heating efficiency, thereby wasting part of the
energy. A large amount of energy is wasted when the burner is fired
and turned off.19 However, a system sized just for the heat demands
of the house does not allow rapid re-heating after the heat control
was turned down during periods of absence. When the occupants take
extended vacations in winter, they turn down the heat to save energy
(and costs). The heater keeps the house at the low level of 55°F
during their absence, requiring a very long time to reheat on
return. Not only must the air temperature be raised, but the
temperature of the thermal mass of the house must also be raised. In
an example of a house with a thermal mass of 10,000 BTU/°F, the
occupants want to raise the house temperature back to 73°F. To raise
the temperature 18° requires 180,000 BTUs of heat, even when outside
losses are not computed (18° F x 10,000 BTU/°F thermal mass =
180,000 BTU). If the energy efficient house has a 20,000-BTU heat
pump, and the outside losses are at 8,000 BTU/hr, it will take 15
hours for the home to reheat before the heater will shut off. (20,000
BTU/hr heat output minus 8,000 BTU/hr heat loss, leaves 12,000 BTU/hr
to heat the house back to normal temperatures. 12,000 BTU/hr x 15
hours = 180,000 BTU.) With a small-capacity furnace or heat pump, the
occupants would be inclined to leave the heat at a livable temperature
during their absence to reduce the reheat time. However, an
“extravagant” 40,000 BTU furnace would allow the house to reach its
temperature in less than 6 hours. (40,000 BTU/hr less 8,000 BTU/hr
heat loss, leaves 32,000 BTU/hr to heat the house back up. 32,000 BTU/
hr x 5.7 hrs = 182,400 BTU.) If the home can be reheated in a
relatively short time, the occupants would be more willing to have the
thermostat set low or off at night or set low during prolonged
absences, since the house could be warmed quickly when necessary. The
theoretical extravagance or wasted energy of an oversized heater is
not valid in all cases. Depending on the lifestyle of the occupants,
it may be preferable to keep the heating system oversized when
prolonged periods of shutoff are anticipated.


Cooling Tubes for Summer Cooling?

Envelope homes utilize underground cooling tubes in summer. Air is
drawn through a 50-to-70-foot- long aluminum culvert pipe 2 feet in
diameter, buried 6 to 7 feet underground.18 Outside air is drawn into
the cooling tube, travels 50 to 70 feet underground, and enters the
house. Heated air is exhausted passively from vents at the top of the
house. The cooling tube allows enough time and distance to cool the
air nearly to ground temperature. This provides nearly free cooling
for the house. The use of such cooling tubes (earth tubes) could
reduce significantly the cooling demand of a well-insulated home in
summer.
Deep in the ground, the temperature stays fairly mild in winter (45°F
when the air is 0°F). The earth tube would partially preheat
ventilation air in winter, reducing the energy needed to warm the
ventilation air. The tubes would also reduce frosting-up tendencies
of the air-to-air heat exchanger when outside temperatures drop very
low.
See the next page, “Potential problems with cooling tubes” for likely
drawbacks on their use.

Cooling tube (earth tube)


As an example, a superinsulated home in Minnesota did precisely that.
21 Fresh air is drawn through a 120-foot-long pipe 12 inches in
diameter buried 8 to 12 feet underground. Outside air brought through
this pipe is warmed by the ground to 45° in winter and cooled to 55°
in summer. Air from the vent is used to supply air to the heat
exchanger. Then the heat exchanger raises the temperature of intake
air nearly to room temperature. Since the air is warmed to 45° in
winter, the whole problem of heat exchanger frost-up is eliminated.
As winter temperatures in Minnesota are frequently below 0°F,
preheating of the air is quite significant. Low-temperature intake
air from the earth tube reduces the need of additional cooling for
most of the summer. When cooling is needed in the summer, the air
from the intake pipe (55° F) is directly routed into the home,
bypassing the heat exchanger core. In this way, cool air enters the
house without having to use air conditioning.
Cooling capability of cooling tubes. In order to eliminate the need
for air conditioning, it is necessary for the cooling tube to provide
cool incoming air to replace the hotter exhausted air. In example 10
of the summer heat gain data, the home gains 144,000 BTUs over a 24-
hour period. This averages 6,000 BTU/hr or 100 BTU/minute. If the
cooling tube were able to supply 55° F incoming air, and the hottest
air exhausted were 80° F, about 225 cfm airflow would remove
sufficient heat to keep the house cool. (225 cfm x 25° ∆T x 0.018
[specific heat and density factor] = 101 BTU/minute.) The Minnesota
superinsulated house referenced kept a steady intake air temperature
of 55° F during the summer. 21

Cooling tube (earth tube)
For ventilation, a 12-inch-diameter metal pipe, 40 to 120 feet long,
buried as deep as the foundation will allow.


A separate trench can be dug for the cooling tube, or the foundation
trench can be used to hold the cooling tube for new construction. A
house with dimensions of 44 feet by 28 feet has an outside perimeter
of 144 feet, more than enough length for a 120-foot air intake pipe
placed at the bottom of the foundation trench before back-filling.
The length of cooling tube needed to provide temperature stability
should be considered. A geo-thermal heat pump used in moist soil in
England provided 46.8 BTU/hr per linear foot of pipe.22 The copper
pipe used was one inch in diameter, which would have a surface area of
38 square inches per linear foot. For each square-inch surface area
buried deep enough underground, the amount of heat that was given off/
absorbed by the ground was 1.24 BTU/hr (46.8 BTU/sq in/hr ÷ 37.7 sq in
= 1.24 BTU/hr). A 12-inch diameter pipe of 120-foot length has 54,280
square inches surface area, which could theoretically give off/absorb
up to 67,315 BTU/hr. To cool air at the rate of 225 cfm from an
outside air temperature of 100°F to 55°F would take only 10,935 BTU/
hr (225 cfm x 0.018 x 45° ∆T x 60 minutes/hr = 10,935 BTU/hr).
Perhaps the cooling tube could be significantly shorter to provide
adequate cooling of the air in the example cited. Dry ground does not
have the ability to transfer heat as rapidly as wet ground; thus drier
ground requires a greater surface area of contact. Considering heat
load of the building, ground temperature at the depth used, and ground
moisture, about 40 to 120 feet of 12-inch-diameter pipe is sufficient
length to cool an energy efficient home. As a minimum depth, the
earth tube should be buried below the frost line. Ground temperatures
tend to be most stable more than 7 feet below the surface. At 20 feet
below the surface of the earth, the temperatures stay essentially
constant year-round.

Potential problems with cooling tubes

Since the cooling tube travels underground, the possibility exists
that joints or seams in the cooling tube could be a source of radon
infiltration by drawing radon in from the soil. This means that a
home with a well-sealed basement, having essentially no radon
infiltration, could now have a new source of radon infiltration
through sealed or unsealed joints in the cooling tube.

Use of a cooling tube, while decreasing air conditioning demands or
decreasing costs of heating ventilation air in winter, could increase
home air quality problems due to radon contamination.41 If radon
contamination is not enough worry, the excessive humidity in cooling
tubes in summer can result in mold and fungus growth.42 As the summer
drags on, the continual flow of hot outside air through the cooling
tube eventually raises the temperature of the surrounding soil. As
the season continues, the cooling tube, therefore, loses its
effectiveness.
All of these factors perhaps make the use of "cooling tubes" of
questionable value. These underground air conduits were considered an
essential part of envelope homes. This is just one more factor
showing that envelope homes have too many potential flaws. Envelope
homes use cooling tubes to supply fresh, cool air in summer. In
actuality the performance of cooling tubes degrades with longer
summers, and cooling tubes have additional risks of air contamination
through radon infiltration and from mold and fungus growth.
Although a cooling tube might keep a house cool, it would not remove
significant humidity. For example, with the outside temperature 90°F
and 50% relative humidity, the cooling tube cools the air to 60°F.
The 60° air coming in from the cooling tube will have essentially the
same total amount of moisture, now nearly 100% relative humidity. It
is therefore necessary to dehumidify cooling tube air that is
introduced into the home during summer. A dehumidifier or air
conditioner can effectively remove excess humidity.
It is possible to get the benefits of earth-assisted cooling (and
dehumidification) in summer without the associated risks of radon or
fungus growth. This method is described several pages earlier in the
section on "geo-thermal heat pumps." By this method, the stable earth
temperatures are used to provide summer cooling and winter heating.
In the summer cooling mode, the geo-thermal heat pump dumps heat into
the soil. In winter, excess heat is extracted from the soil. With
geo-thermal heat pumps, there is still decreased effectiveness late in
the summer season. However, after the end of the summer, this excess
heat in the soil might slightly increase the effectiveness of the
system early in winter.

Indoor humidity control in summer

Dehumidification is important for effective cooling. A dehumidifier
or an air conditioner can remove excess humidity in summer. A
dehumidifier is similar to a small air-conditioning unit in having a
heat pump compressor and cooling coils to condense humidity. However,
the heat pump of the dehumidifier transfers the heat into coils just
behind the cooling coils. As air passes through a dehumidifier, air
is drawn in by the fan, passes over the cooling coils (becoming both
cooled and dehumidified), passes over the heat coils (becoming
reheated), and exits the dehumidifier with less moisture but slightly
warmer than it entered. The increased heat of the air is due to the
operating heat given off by the unit.
An air conditioner has the basic parts of the dehumidifier, except
that the cooling coils are inside the house and the heating coils are
outside. The air conditioner requires an inside and outside fan
unit. However, fan power is a relatively small part of the total
power consumption of the unit. For nearly the same energy cost (air
conditioner versus dehumidifier), the air conditioner provides the
added advantage of cooling. If one needs cooling along with
dehumidifying, it makes more sense to use a small air conditioner
rather than a dehumidifier.

How Much Insulation Is Actually Needed?

McGrath explains a formula for determining the amount of insulation
to be used in walls, ceilings, and floors in a given climate.

R-value needed = Heating degree-days x 0.004

McGrath termed this formula the Roggasch variable R value rule, named
for the person who empirically determined the formula. It postulates
that a building can afford to lose 6,000 BTU from each square foot of
its exterior surface in a year. The heating degree-days value (DD)
for the year is used to arrive at the insulation level needed. (DD ÷
R-value x 24 hours = 6,000 BTU/year. Rearranging this formula, we get
R = DD x 24 ÷ 6,000. Therefore R-value = DD x 0.004.)
Superinsulation theorists in Alaska feel that all external surfaces,
walls, ceilings, and floors (fixed building sections) have essentially
the same outside temperature and should be equally insulated. 2
Using this formula, the arctic areas of Alaska would need about R-60
in the fixed building sections.

R = 14,500 degree-days (Fairbanks, Alaska) x 0.004 = R-58

Similar calculations can be made for other climates. Duluth,
Minnesota (10,000 degree-days), needs R-40 fixed building sections.
Helena, Montana (8,129 degree-days), needs R-32. Denver, Colorado
(6,300 degree-days), needs R-25. Under this formula, Savannah,
Georgia (1,850 degree-days), needs only R-7. Unfortunately, the
formula does not take cooling demands into consideration. Therefore,
heating degree-days are quite inaccurate in climates where air
conditioning is the main concern for most of the year.

Heating degree-days, cooling demands, and insulation levels

In areas where air conditioning is a requirement for reasonable
comfort in summer, modification of the insulation-sizing formula is
necessary to take cooling costs into consideration. One way to
explain the costs for year-round climate control is:

Heating costs + Cooling costs = Climate control costs

To relate climate control costs to heating demand (i.e., heating
degree-days):

Climate control costs ÷ Heating costs x Heating DD = Climate
DD


If the winter heating bills total $200 and the summer cooling bills
total $200, the climate control costs are $400 for the year. Using
these values in the climate degree-days formula, we find that the
climate control costs are twice the utility costs expected by heating
degree-days alone.

$400 ÷ $200 x Heating DD = 2 x Heating DD = Climate
degree-days

To take these formulas one step further, the resulting climate degree-
days are plugged back into the insulation formula:

Climate degree-days x 0.004 = R-value needed.

Savannah, Georgia, energy utilization example. To illustrate the use
of these formulas, the actual 1984-85 heating and cooling costs of a
home near Savannah, Georgia, are used in calculations.
House features: 1,850-square-foot single-story ranch, slab on grade
with the following energy factors: walls: R-13; ceiling: R-35; floor:
no perimeter insulation; windows: double-glazed (aluminum frames with
no thermal break); north windows: 88 sq ft, south: 75 sq ft, east: 6
sq ft. The roof overhangs provide complete summer shading and 75%
exposure in winter.
During the 1985 summer months, the electricity rates rose, reaching a
net increase of $130 for the cooling season. During the 1984-85
winter, the gas rates rose, to a net increase of $110 for the heating
season. These figures are determined by calculating the average
electricity bills during months when air conditioning was not used.
This baseline cost is subtracted from the electric bills during months
when air conditioning was used. Gas costs for winter are similarly
determined by subtracting baseline gas usage from winter gas usage.
The cooling bill (central air conditioning) was about 18% greater than
the heating bill (central gas furnace). While this is comparing gas
heat and electric air conditioning, it still gives us some basis for
comparison. In using the formulas:

Heating costs + Cooling costs = Climate control costs
$110 + $130 = $240

Climate control costs ÷ Heating costs x Heating DD = Climate
DD
$240 ÷ $110 x 1,850
= 4,036

Climate degree-days x 0.004 = R-value needed
4,036 x 0.004 = 16, or R-16 needed for
the building

Summary: The Roggasch insulation sizing formula is accurate for cold
climates not requiring summer cooling. The above climate degree-days
formulas may be helpful in deciding the level of insulation needed for
year-round economy. The original insulation formula suggested that
R-7 was sufficient for the 1,850 degree-day example. However, when
cooling demands are considered, the insulation level should be about
R-16.

The example home in Savannah, Georgia, does not show utility costs
typical of the area. Usual heating and cooling rates are considerably
higher for neighboring homes. The house referenced is a new home,
meeting the regional criteria for energy conservation. It has
significant upgrades in attic ventilation and insulation; it has
radiant barriers in the walls although it lacks an attic radiant
barrier and vapor barrier. The house has nearly optimum solar
orientation, allowing passive solar gains in winter with complete
summer shading by the roof overhangs. Although its utility costs are
quite low for the area, they show the relative proportion of winter
versus summer utility rates. Such calculations can be carried out for
other geographical areas if heating and cooling bills are known.
In climates where the summer nights cool off, nighttime whole-house
ventilation can drop the temperature of the thermal mass of the house
to eliminate or reduce the need for daytime air conditioner use. If
an air conditioner must be used, nighttime usage is also more
economical due to the lower indoor to outdoor temperature extremes.

Other measures of insulation need

Essentially all insulation recommendations for use in the lower 48
states prescribe more insulation in the attic than in the walls or
floors. In winter, most homes have stratification of the air in the
house, meaning hot air is near the ceiling and the cold air is near
the floor. Hot air rises and cold air is produced by contact with
cold windows, walls, floors, and ceilings. The supply of cold air
from cold surfaces increases temperature stratification in homes.
Since the warmest air is near the ceiling in most homes, it makes
sense to have additional attic insulation to reduce heat loss. Floor
temperatures are usually moderated by the ground for slabs, crawl
spaces, and basements and do not need to be as heavily insulated as
the attic, except in severely cold climates. For well-insulated or
superinsulated houses stratification is less of a problem.
During summer, attic temperatures in the lower 48 states tend to rise
much higher than outside air temperatures, causing much heat gain
through the ceiling. This makes the house more uncomfortable and more
expensive to cool. By comparison, the ground usually moderates floor
temperatures unless the floor is over an open-air deck. An attic
radiant barrier, increased attic ventilation, and increased attic
insulation levels can reduce a significant portion of summer heat gain
in hot climates.
A 1983 publication from Canada recommends the following insulation
levels in southern Canada and the northern half of the Unites States:
ceilings: R-40; frame walls: R-30; foundation walls: R-20; and R-10
below the foundation floor.6 Another recent publication shows similar
recommendations for insulation in walls and ceilings, with R-30 to
R-16 for floor and slab insulation. (R-30 is used for slabs when the
floor is within 5 feet of a ground water source.) 23 The Minnesota
superinsulated house has R-46 for the walls, R-20 below the basement
slab, and R-70 loose fill in the attic.21


Heating Costs for the Year

Using the earlier calculations on winter heat loss, it is possible to
estimate fuel costs for the heating season. As shown earlier in this
book, insulation levels make substantial differences in heat loss in
cold weather. Heating systems and energy habits of the occupants also
make substantial differences. Occupants using 78° indoor temperatures
in winter use significantly more heat than when keeping a 62° inside
temperature. In most locations, electric heat is more expensive than
gas or oil heat.
To make some heating estimates, the below energy cost factors will be
used. (These calculations were based on prices as of 1990.)

1. Electrical resistance heat, at $0.07 per kilowatt hour (KWH), 100%
efficient, providing 3,413 BTU/KWH; the cost is $20.50 per million
BTU.
2. Gas heat, at $0.44 per 100 cubic feet; gas yields 1,000 BTUs for
each cubic foot; a 93% efficient furnace produces 930 BTU/cu ft, for a
net cost of $4.73 per million BTU.
3. Fuel oil, at $0.90 per gallon; each gallon yields 138,000 BTUs; 85%
efficient combustion provides 117,300 BTU/gallon, a net cost of $7.67
per million BTUs.

Actual energy prices have much variation throughout the country, and
over time, so separate calculations will be needed for current costs
in your area.

House examples from winter heat million BTUs electric heat oil heat
gas heat
loss calculations, for one day used/day costs costs costs

1 (uninsulated home) 1.619 $33.19 $12.41 $7.65
2 (normally insulated home) 0.538 11.03 4.13 2.54
3 (superinsulated, no heat exchanger) 0.262 5.37 2.01 1.24
4 (superinsulated with heat exchanger) 0.159 3.26 1.22 0.75
5 (example 4, with a sunspace) 0.127 2.60 0.86 0.60

The number of degree-days for a specific day is the average of the
high and low temperature subtracted from 65°. Example: with a high
of 35° and a low of 5°, there were 45 degree-days for that day ([35 +
5] ÷ 2 = 20; 65 - 20 = 45 degree-days). For the winter heat loss
calculations of the six example houses, the high was 20°F and the low
was -10°F, resulting in 60 degree-days for the day (20 + [-10] =
10; 10 ÷ 2 = 5; 65 - 5 = 60 degree-days).
In a 6,000-degree-day (DD) climate, 60 DD is about 1% of the cold
weather for the year. To estimate the fuel costs for the winter in
this climate, the heat used for the one day (60 DD) could be
multiplied by 100, indicating a gas heat cost of $765 per year for an
uninsulated house and $75 for a superinsulated house. In reality, a
6,000 DD climate does not have 100 days of weather described in the
example calculations. In fact, such temperatures might not even be
reached in an entire heating season. Instead, the heating season is
longer (about eight months long) and usually less severely cold.


Below is listed the heating degree-days for two different climates:
the 5,429 DD climate of Springfield, Illinois, and the 10,000 DD
climate of Duluth, Minnesota. The heating season is broken down into
degree-days for each month. The average temperature in each month
used in these calculations is the number of degree-days for that
month, divided by the number of days in that month, subtracted from
65° (This data is derived from Designing and Building a Solar House,
by Donald Watson.)

Springfield, Average Duluth, Average
Illinois, temperature Minnesota, temperature
Month degree-days in month (°F) degree-days in month (°F)

July 0 over 65° 71 63°
August 0 over 65° 109 62°
September 72 63° 330 54°
October 291 56° 632 45°
November 696 42° 1131 27°
December 1023 32° 1581 14°
January 1135 28° 1745 9°
February 935 32° 1518 11°
March 769 40° 1355 21°
April 354 53° 840 37°
May 136 61° 490 49°
June 18 64° 198 59°
Year Total 5,429 10,000

As explained above, the average temperature during each month can be
determined from the degree-days for each month using the formula:

65° - (DD ÷ Number of days in the month) = Average
temperature for month.

To calculate heat loss of a building, the temperature difference
between inside and outside must be determined. If the outside
temperature is 10°F and the inside of the house is kept at 70°F, there
is a 60° ∆T. For the 10° outside temperature, a 62° indoor
temperature results in a 52° ∆T, although a 78° indoor temperature
makes a 68° ∆T. In this way, the energy habits of the occupants can
have significant effects on the utility bills. For these
calculations, 70°F is used as the indoor temperature. Therefore, to
determine the ∆T in the calculations, this formula is used:

70° - Average temperature for the month = ∆T

The net heat requirement is calculated for each home type by this
formula:

Heat loss (in BTU/°F/24 hours) x ∆T, minus the solar and internal
gains for the day x Number of days in the month = Heat demand for
the month.

For these calculations, all house specifications are kept the same as
used in the example houses. The internal gains are kept at 36,000 BTU/
day. The solar gains are computed based on the latitude, percent
sunshine, and types of windows used in the example houses. The heat
loss is calculated based on the ∆T for the locations listed.

Sample calculation. House example 2 for Springfield, Illinois, has a
heat loss of 405 BTU/°F/hr; multiplied by 24 hours, this is 9,720 BTU/
°F/24 hrs; with 42° ∆T for January this is a loss of 408,240 BTU/24
hours. For an average 47% sunshine for the month, there are combined
solar and internal gains of 90,295 BTU/day. This leaves a net loss of
317,945 BTU/day. This is 9,856,295 BTU loss for the 31-day month, or
9.856 million BTU heat loss for January. In the two tables below,
combined solar and internal gains are listed for the example houses in
various months. Example 1 has single-pane windows, resulting in
greater solar gain than double-pane (example 2), or triple-pane
(examples 3 and 4). Example 5 has a south-facing sunspace, increasing
the solar gain.

Springfield, Illinois
Month % Sunshine Net solar and internal gains
(BTU/24 hours) for example houses
1 2 3, 4 5

September 73% 127,171 115,975 104,778 138,544
October 64% 120,542 110,160 99,777 138,630
November 53% 104,358 95,964 87,564 120,554
December 45% 91,632 84,800 77,968 105,266
January 47% 97,896 90,295 82,693 112,622
February 51% 106,150 97,535 88,920 121,303
March 54% 103,094 94,964 86,615 115,023
April 58% 93,252 86,416 79,357 99,899
May 64% 90,747 84,024 77,300 92,892
June 69% 93,252 86,221 79,190 94,591


Duluth, Minnesota
Month % Sunshine Net solar and internal gains
(BTU/24 hours) for example houses
1 2 3, 4 5

July 68% 106,117 97,507 88,896 112,061
August 63% 106,846 98,146 89,445 116,578
September 53% 103,322 95,055 86,787 116,055
October 47% 95,438 88,139 80,839 108,949
November 36% 74,570 69,834 65,097 84,150
December 40% 74,070 69,395 64,719 83,837
January 47% 87,517 81,191 74,864 100,394
February 55% 108,639 99,719 90,798 125,351
March 60% 115,638 105,858 96,077 131,232
April 58% 103,015 94,785 86,555 112,551
May 58% 96,668 89,218 81,767 102,074
June 60% 99,042 91,300 83,558 102,323

A superinsulated home can reduce the length of the heating season,
since heat is not needed until temperatures drop to low levels. To
illustrate this point, calculations are made for winter heat loss for
the six example houses. The heat demand is listed in the tables as
millions of BTU/month. The true heat consumption for a house depends
on the actual temperatures and amount of sunshine. In the following
examples, the calculations are based on long-term average heat demands
and expected sunshine for the locations listed (data derived from
Designing & Building a Solar House).

5,429 degree-day climate: Springfield, Illinois, for the six example
houses, using solar gain calculations based on 40° north latitude

Month ∆T 1 2 3 4 5

September 7° 1.814
October 14° 7.710 0.804
November 28° 19.085 5.286 1.869 0.538
December 38° 28.337 8.821 3.888 2.022 1.175
January 42° 31.425 9.856 4.405 2.342 1.415
February 38° 25.180 7.611 3.205 1.519 0.613
March 30° 21.404 6.099 2.292 0.819
April 17° 10.674 2.365 0.349
May 9° 4.570 0.128
June 6° 1.937

Million BTUs used/year 152.136 40.969 16.008 7.240 3.203

Gas heat costs/year $719.60 $193.78 $75.72 $34.25 $15.15

10,000 degree-day climate: Duluth, Minnesota, for the six example
houses, using solar gain calculations based on 48° north latitude

Month ∆T 1 2 3 4 5

July 7° 2.416
August 8° 3.215
September 16° 9.585 1.820
October 25° 17.539 4.801 1.642 0.415
November 43° 31.920 10.444 4.951 2.908 2.336
December 56° 43.677 14.723 7.285 4.535 3.942
January 61° 47.359 15.864 7.800 4.805 4.013
February 59° 40.689 13.265 6.299 3.682 2.715
March 49° 36.613 11.483 5.151 2.745 1.655
April 33° 23.100 6.779 2.702 1.134 0.354
May 21° 14.215 3.562 0.949
June 11° 5.735 0.469

Million BTUs used/year 276.063 83.198 36.779 20.224 15.015

Gas heat cost/year $1,305.78 $393.55 $173.96 $95.66 $71.02

When looking at the above data, one can see that normal insulation
uses only 30% of the space heating costs compared to an underinsulated
house (examples 1 and 2). Superinsulation (example 4 versus example
1) uses less than 8% of the space heating costs compared to an
underinsulated house. Adding a sunspace (example 5) seems to give no
more than $25 in space heating savings, compared to superinsulated
design (example 4). The addition of a sunspace, just to save heating
costs, is not cost-effective.
Existing technology provides other ways of reducing heating costs:
(1) by use of a sunspace, (2) R-60 walls and floor combined with R-70
ceilings, (3) quadruple pane east/west and north windows,

and (4) use of R-15 insulating shutters on the windows during the
night (12 hours/ night). The calculations below represent the net
heat needed for the 10,000 degree-day climate in Duluth, Minnesota,
for various insulation upgrades, using the same house size described
earlier.

Duluth, Minnesota, for the listed insulation upgrades
Shutters
Shutters Quad E/N
Sunspace Quad E/N Quad E/N Sunspace
Month ∆T R-60/70 R-60/70 R-60/70 R-60/70 R-60/70

November 43° 2.103 1.531 1.974 1.386 0.814
December 56° 3.452 2.859 3.266 2.474 1.882
January 61° 3.625 2.833 3.433 2.570 1.779
February 59° 2.652 1.684 2.515 1.761 0.794
March 49° 1.797 0.707 1.725 1.032
April 33° 0.516 0.531 0.080

Million BTUs used/year 14.145 9.614 13.444 9.303 5.269

Gas heat cost/year: $66.91 45.47 63.59 44.00 24.92

Adding shutters has only a $20 annual space heating savings in the
above examples. To eliminate the need for furnace heat, it would be
necessary to add at least 150 square feet of solar collectors on the
south wall for the final example house (shutters, quadruple pane east/
north windows, sunspace, R-60 walls, floors, and R-70 ceiling).
Avoiding any use of auxiliary heat requires extreme measures in this
cold climate and is not cost-effective at current energy prices.

Applications of Energy Technology to New Homes

Standard house insulation

Walls. The limiting factor for insulating standard walls is space.
With 3½" of space between the wallboard and sheathing, the amount of
insulation is usually R-11. Studs and framing take up 15% or more of
the wall area, resulting in a significant amount of wall conduction
and reducing the final insulative value of the wall to below the R-11
level. Using 2x6 inch framing, there is 5½ inches of insulation space
(R-19 batt) and the stud spacing can be wider, reducing the amount of
stud conduction. Rigid insulation board sandwiched either inside or
outside the stud framing increases the final insulation value.
External insulative sheathing can induce condensation problems within
the wall. However, vapor-permeable external foam boards with
perforated radiant barriers are available that do not induce
condensation when properly installed. A continuous vapor barrier is
very difficult to achieve with a standard wall (whether 2x4 inch or
2x6 inch framing) because wiring and piping pierce the vapor barrier
and allow air infiltration and water vapor leakage. In standard
construction, an infiltration barrier (Tyvek® or other housewrap) used
over the exterior sheathing reduces heat loss by reducing infiltration
and by preventing wind from blowing into the insulation. Infiltration
barriers are especially useful in houses where the builder did not use
a continuous vapor barrier on the inside wall.




Ceilings. Attics of standard homes usually allow sufficient space
for large amounts of insulation in the ceiling. Twelve inches (R-35)
to 24" (R-70) of loose fill insulation are often used in well-
insulated attics. Use continuous soffit vents, gable vents, and ridge
vents, or the equivalent, to provide ventilation needed to remove
attic moisture. The local building code usually specifies the amount
of vents used in the attic. Use no less than 1 square foot of open
vent space for each 300 square feet of attic. About 50% of the vent
area should be soffit vents; the remainder should be gable and/or
ridge vents. A vapor barrier should be provided on the inside surface
of the ceiling between the ceiling sheetrock and insulation to reduce
moisture migration into the attic. Alternatively, one can retrofit a
continuous attic vapor barrier. (See page 78 for suggestions about
retrofitting attic vapor barriers.)
Shed roofs, flat roofs, and some vaulted ceilings limit the space for
insulation and ventilation, sometimes to only 5½ inches. Even when
space is limited, ventilation is still necessary to remove moisture in
winter and excess heat in summer.
Conventional roofs usually have insufficient space for insulation and
ventilation over the top plate of the wall. Because of the typical
bird's mouth cut in the 2x6 roof rafter, the space over the top plate
is less than four inches. If insulation is not carefully installed,
the ventilation passageways over the top plate can be blocked and
attic condensation can occur. Changing the roof-framing design can
allow for proper ventilation and insulation depth over the top plates
in the attic.



A radiant barrier installed in the attic reduces radiant heat gain in
hot climates and radiant heat loss in cold climates. Insure plentiful
attic ventilation to remove excess summer heat and to reduce
overheating of the roofing material. A radiant barrier used in walls
also reduces heat loss and gain. A radiant barrier can be used at the
plane of the vapor barrier, or a perforated radiant barrier should be
used in exterior parts of insulated walls or ceilings, the
perforations allowing moisture to escape.


Floors. Basement walls and floors need insulation; the ground is not
an insulator. Insulation boards can be installed during construction
to cover all exterior surfaces of the basement. In milder climates,
it may be sufficient to use perimeter insulation. Heat escaping from
uninsulated basement walls reduces freezing of the ground near the
wall. When insulation is added to the wall, freezing of moist ground
near the basement wall can actually cause foundation cracks due to
ground expansion during freezing. Backfilling with gravel or reducing
moisture levels outside the wall can reduce frost damage to foundation
walls. Insulating basement walls interiorly increases the risk of
frost damage; because the concrete foundation conducts heat out of the
ground faster than the surrounding earth, freezing of the surrounding
ground is accelerated. When insulating interiorly, also add some
exterior insulation (e.g., rigid foam insulation) to reduce heat
conduction out of the ground through the basement walls.
The floor joists, often 9 to 12 inches in depth, above crawl spaces
usually provide ample space for insulation. Less insulation is
usually installed for the floor than the ceiling, since the warmest
air is near the ceiling. Floors and walls should have similar amounts
of insulation. In colder climates, the amount of heat lost from the
floor increases, requiring more floor insulation. Ventilate the crawl
space to remove moisture.
Windows. At least double-pane glass, with nonconductive framing,
should be used. Metal frame windows should be limited to types having
a thermal break. If there are no data to show that a thermal break is
provided in a specific metal frame window, no thermal break is likely
to be present. A proper amount of south windows should by used; in
most areas of the country, it is advisable to minimize east, west, and
roof windows, particularly important in the southern United States.
North-facing windows have little solar gain, and do not significantly
increase air-conditioning bills, but add to heating bills in winter.
South windows should have an appropriately-sized overhang to shield
the sun in summer and to allow solar gain in winter. (See the section
in part four covering overhang designs.)
Ventilation. The home will need a method of supplying fresh air when
there is an effective vapor barrier. Running bathroom exhaust fans
may or may not remove enough stale air for proper ventilation.
Opening windows may be needed to get fresh air or to feed the exhaust
fans. In some cases, it may be more economical to provide whole-house
ventilation by use of an air-to-air heat exchanger.
Having a poor vapor barrier risks internal wall condensation and
rot. An effective vapor barrier and good weather-stripping cause air
quality problems unless ventilation is otherwise provided for.
Piping. Even in southern climates, it is possible for water pipes to
freeze within exterior walls in winter. There is simply not enough
space in a 3½ inch external cavity wall to have enough insulation to
assure that pipes in these walls will not freeze, even if most of the
insulation is exterior to the pipe. There are numerous freezing
disasters in winter, even in the southern United States. Piping is
not always buried deep enough in the ground to be below the winter
frost line. It is common for pipes to run through the middle of
exterior walls, attics, crawl spaces, and above carports and garages.
Some outside faucets are not provided with inside shutoffs. When
pipes go through potentially cold areas they must be insulated
properly to prevent winter freezing and summer condensation.

Ducts. Ventilation ducts passing through unheated spaces should be
thoroughly insulated. These ducts can cause major losses of energy
due to the temperature extremes between the duct and the surrounding
areas. It is common for such ducts to have a thin foil-backed
insulation cover, not adequate to conserve energy. A 6-inch-thick
insulation blanket should be added to the ducts.

The superinsulated house

Walls. A backward double wall is most effective for superinsulation.
It provides the space for insulation, allows for a continuous vapor
barrier, and protects the vapor barrier for the lifetime of the
house. The insulation value used is dependent on the climate demands
of the area, as related to heating degree-days and cooling demands;
R-30 to R-50 is a range suitable for the northern United States and
southern Canada. Exterior insulative sheathing should be avoided to
prevent moisture condensation in walls. The backward double wall
technique allows the necessary insulation to fit into the exterior
wall cavity by either batt or loose fill insulation. The exterior
sheathing and siding should have at least 3 to 5 times the
permeability of the vapor barrier to prevent moisture condensation.
Overlap all vapor barrier junctions and seal the joints properly to
assure continuity of the 6 mil polyethylene vapor barrier. Pay
special attention to the vapor barrier near junctions of internal
partitions to obtain continuous ceiling and floor vapor barriers.
Insulation blankets should be installed at right angles for each
successive layer. For example, use an R-30 insulation roll in
horizontal layers in the central cavity of the double wall, then
install the R-11 batts vertically between the studs. Alternating
between horizontal and vertical insulation layers will minimize
convective air movements within the wall.




Ceilings. Enough attic space for 12 or more inches of insulation
should be provided. The more severe the climate, the more insulation
should be used. Wires, pipes, and ducts should be routed through the
walls and between floors so that the vapor barrier of the ceiling is
not broken. Alternatively, a continuous vapor barrier can be retrofit
in the attic (see page 78).
Provide at least 12 inches of insulation over the top plate of the
inside wall. The insulation of the attic should be continuous with
the insulation of the walls. If rolls or blankets of insulation are
used in the attic, install the layers at right angles. The first
layer is placed between the ceiling joists, and the second layer is
put at right angles to the joists, on top of the first layer of
insulation. Provide good attic ventilation to remove moisture.
Floors. There should be a continuous vapor barrier to prevent
moisture migration. Floors above crawl spaces should have amounts of
insulation similar to those of walls. Additional floor insulation can
be added by strapping and crosshatching techniques. The insulation
can be secured in place with insulation support netting. See the
section on retrofitting for other techniques to hold up the
insulation. The crawl space should be well ventilated to remove
moisture and to prevent the entry of radon from the ground. Moist
ground should be covered with 10-mil polyethylene.
Windows. Double- or triple-glazed windows provide reasonable energy
efficiency for south windows; plan to use triple-pane or low-E glass
for all other orientations. Use a suitable amount of south window
area for passive solar gains. The low-E glass coatings reduce heat
loss in winter and heat gain in summer by blocking infrared heat
waves. Low-E windows still allow passive solar heating, although they
block some of the solar energy transmission. Insulated shutters and
shades covering windows on cold nights can cut down on space heating
demands. Since windows are constructed to fit in standard wall
thicknesses, the additional thickness of a superinsulated wall
complicates the installation.

Window framing for superinsulated walls



The window can be mounted in the inside 2x4 inch framing or the
outside curtain wall framing or by beveling the casing to a position
in between the two points. The vapor barrier position seems better
when the window is at a more exterior position; this allows the proper
amount of insulation exterior to the vapor barrier joint. It is
possible to bevel the casing near one of the stud walls and then
attach an additional storm window to the framed space of the nearby
wall (inside beveled casing having a double-pane window and an outside
single-pane storm window).





If window shutters are desired, the shutters can be designed to fit as
a pocket within the superinsulated wall. Inside the wall and between
the windowpanes, the shutters are protected from inside condensation
and outside snow, rain, and cold. 2 (One opens the inside window to
operate the shutter, or the shutters can be hooked to pull cords to
open and close.)



Ventilation. It is necessary to provide fresh air for the house,
since infiltration has been nearly eliminated. It is best to route
bathroom and kitchen vents to a common point for attachment to the air-
to-air heat exchanger. The outside duct for air intake should be
positioned as far as possible from likely sources of contaminated air;
position it away from sources of car exhaust and fireplace emissions
and from the direct airflow of the heat exchanger exhaust vent.
Outside air can be economically preheated by the heat exchanger.
However, in very cold winter climates the exchanger core can
potentially freeze and not allow sufficient airflow for proper
operation. There are a few possible methods to defrost the exchanger
core. 1) Use a solar panel on the south wall to preheat intake air.
26 2) Have the intake air fan shutdown on a specific schedule to
allow the warmer exhaust air to thaw the core.27 3) Manually defrost
the exchanger by shutting down the exchanger and routing room air
through the exchanger until it thaws. 4) Install electrical
resistance heating coils in the intake air stream to defrost the
exchanger when necessary. There are various problems with these
methods: Cold days without sunshine will not allow the solar panel to
defrost the core. Shutting off one air stream causes air imbalance
throughout the house. Manual defrosting requires additional, more
complicated ductwork. Using an earth tube to pre-warm the exchanger
air could prevent frosting of the exchanger core, however, problems
with radon infiltration make this method unsafe.
Since the home is constructed very tightly, all combustion appliances
must have outdoor air supplied directly to them. Without direct air
supply, combustion air might be drawn through the exhaust flue,
returning dangerous gases to the house. Without direct air supply, a
fireplace would have difficulty removing exhaust and sustaining
combustion, putting occupants of the house at great risk from
contaminated indoor air.

To allow adequate circulation of ventilation air between rooms,
provide a one-half to one-inch space at the bottom of doors or install
vents in the room doors; this will assist the circulation of air
between the intake and exhaust vents of the heat exchanger duct
system.

Vent positions for air-to-air heat exchanger

Exhaust the air from bathrooms, kitchen, and laundry. Introduce fresh
air into all other rooms of the house for best distribution. Provide
a one-half to one-inch space at the bottom of inside doors to allow
ventilation air to circulate.

Provide supply and exhaust vents for the basement; if only exhaust
vents are provided for the basement, the negative air pressure can
actually cause increased radon gas infiltration. Providing positive
air pressure to the basement will in effect reduce radon
infiltration. Air should be exhausted from the kitchen, bathrooms,
and laundry room (if clothes are hung up to dry). New homes tend to
have more contaminants than older homes due to the paint, glues, other
chemicals, and moisture in new construction materials. Initially it
is a good idea to provide ventilation of 1.0 air changes per hour to
remove these contaminants. After the first year, the ventilation rate
could be decreased to 0.5 air changes per hour unless contamination
persists. Radon contamination may require higher airflow rates, used
on a permanent basis.
Radiant barriers. A radiant barrier can be placed at various points
in superinsulated walls. A radiant barrier can be placed within the
wall at the position of the vapor barrier or a perforated radiant
barrier used on the most exterior part of the wall. A radiant barrier
can be installed in ceiling insulation layers or attached to the top
chord of the roof truss. In order to reflect heat rays in winter, the
radiant barrier might be more effective if near the inside of the
house to prevent any of the radiant heat from being absorbed in the
attic. In hot climates the objective is to keep the heat radiation
from entering the home; the radiant barrier mounted on the roof rafter
or top chord of the roof truss is probably more effective.





For alternative locations of where to place radiant barriers (such as
in attics) see the diagrams on pages 17 and 18.

Provide plenty of continuous attic ventilation above the attic
radiant barrier to remove excess summer heat. A radiant barrier will
also prevent heat loss in winter through the floor above a crawl
space. Thus a radiant barrier can be installed appropriately within
the floor or a perforated radiant barrier can be installed on the
exterior of the floor insulation. Radiant heat is less intense,
although similar to microwaves in a microwave oven. In those ovens,
the door often has a window with a metal grid, perforated enough to
see through, yet the heat radiation is contained within the oven.
Similarly, a perforated radiant barrier reflects heat radiation yet
allows moisture to escape.
A reflective air space is necessary for proper performance of a
radiant barrier. If a reflective air space is not provided, some of
the reflected heat radiation is concentrated next to the surface of
the radiant barrier; the heat trapped in that area will be conducted
from the radiant barrier to surrounding building materials. These
surfaces can then re-radiate the received heat, even though the
radiant barrier itself does not radiate heat very well. For the same
reason, if the radiant barrier gets a layer of dust on it, the dust
can absorb and re-radiate the heat.
Piping. With a backward double wall, piping and wiring can be routed
freely through the inner wall, since they will not break the plane of
the vapor barrier. With R-30 to R-40 exterior to the inside wall,
there is no danger of freezing if water pipes are in the inner wall.
Avoid installing pipes in attics and crawl spaces. If water pipes
must be routed in these areas, they should be very well insulated. In
very cold climates, such as areas of Alaska, pipes going outdoors are
wrapped with heat-producing wires and then covered with thermal
insulation to prevent freezing.
Wiring. Wiring confined to uninsulated areas poses no problems.
However, various texts have conflicting comments about wiring buried
deep in house insulation. Electrical wires have resistance, which
produces heat. If the wires are run at more than their rated
capacity, the excess heat could be trapped near the wires and
potentially cause melting of the electrical insulation around the
wires, especially if the wires run through thermal insulation (e.g.,
insulation batts or loose fill). The heat is retained near the wires
and cannot dissipate, risking an electrical fire. Some texts state
that wires and heat-producing electrical fixtures should not contact
thermal insulation. The backward double wall can avoid this whole
problem without losing thermal performance of the building; the wires
can be routed safely through the internal wall and not contact the
thermal insulation. Wires routed through attics will have contact
with thermal insulation and could pose some risks.
Recessed lighting fixtures near thermal insulation have been
identified as potential fire hazards. One approach is to build (large
enough, wooden) boxes around the recessed lighting fixtures, to
provide the recommended (3”) air space. Then put the proper amount of
thermal insulation, exterior to the box that was built around the
lighting fixture.
Ducts. Heating and cooling ducts should be placed within the thermal
enclosure and not go through unheated spaces. If they must pass
through unheated spaces, they should be well insulated.

Methods of making a superinsulated wall

The backward double wall can be arranged to provide the insulation
level desired by separating the inside and outside wall to the
appropriate thickness. If the inside wall is the load-bearing wall,
the house can be built in the conventional platform method. The floor
joists are cantilevered to the projected position of the exterior
curtain wall.

Alternatively, the house is assembled in the normal fashion and the
curtain wall is attached to the original wall by ledger plates and
joist hangers. Pay special attention to the placement of the vapor
barrier so that it can be attached to the ceiling and floor vapor
barriers. The roof overhang must be wide enough all the way around
the house to allow for the thickness of the curtain wall. Design the
attic with enough space to hold the full depth of insulation over the
outer walls.




















One method is to modify an oversized roof truss to have the inside
wall as the bearing point -- the truss is cantilevered outward from
the load-bearing wall. With standard roof framing, an appropriately
sized overhang is designed, similar to an overhang used for a porch,
to allow sufficient insulation over the exterior walls and to provide
proper shading. See the section in part four describing methods for
determining overhangs for south-facing windows.
It is also possible to make an inside double wall instead of
cantilevering the backward double wall. In this method, the exterior
wall is assembled in the conventional fashion. Massive exterior
siding, such as brick or stone, can be used with this method, if
desired. When the exterior of the home is completed, the insulation
layers are put in place. The inside walls are assembled on the floor
with sheathing and vapor barrier and are tilted into place. If loose
fill insulation is used, the insulation is added after the inside wall
is put in place. This method might require using the next larger size
floor joists (e.g., 2x12 instead of 2x10 inch) since the inner wall
position adds one foot to the floor span; also, the weight of the
insulation and inside wall must be carried by the floor, requiring
greater floor strength. The piping and wiring are routed freely
through the inner wall, since they will not disturb the vapor
barrier.

Retrofitting Insulation in Existing Homes

Retrofitting is a relatively new term used to describe the process of
adding something formerly not present. Retrofitting insulation means
to add insulation to previously uninsulated or poorly insulated areas
of a building.
Compared to a home being constructed, an existing home is far more
difficult to insulate. The attic can be insulated when there are open
attic spaces. Shed roofs and cathedral ceiling roofs provide little
space for retrofitting insulation short of replacing the roof or
lowering the ceiling from the inside. Exterior walls are closed on
both sides with siding or wallboard, making retrofitting very
difficult. Basement slabs and slab on grade floors are already
poured; it is impossible to insulate under them. Aside from adding
attic insulation, no significant insulation is usually added after
completion of the building.
Adding insulation to existing walls will usually require some rather
extreme measures and is very expensive. Below are possible options
for wall retrofitting.

1. One option is to add insulation to empty wall cavities. However,
the blow-in or foam-in techniques have their disadvantages. The major
problem is the absence of a vapor barrier. With insulation added to
existing walls, the moisture that enters the wall will be retained in
the insulation, and eventually lead to rotting of the wall. Painting
the inside walls with two coats of a vapor barrier paint reduces
moisture penetration into the wall. This method of insulation is
limited to achieving the standard level of insulation. Another
problem with blow-in insulations is a tendency for the insulation to
settle. A specific adhesive (Blow-in Blanket®) uses special machinery
to mix it with blow-in insulations to reduce the settling. As the
adhesive cures within the first few hours, it causes the insulation to
harden into a solid mass.5

2. Another way is to construct new inside walls, adding insulation
between the original wall and the new inside wall. Adding insulation
interiorly requires replacing and moving electrical outlets and any
pipes in exterior walls; it disrupts life within the home due to all
the construction being done inside. It reduces the size of the
existing rooms. It becomes nearly impossible to get a continuous
vapor barrier.
3. If the house is in need of new siding, the cost of adding
insulation exteriorly may be reduced effectively. By adding
insulation exteriorly life inside the home is not disrupted, since all
the work and much of the noise are on the outside. To add insulation
exteriorly, the roof must have overhangs wide enough to allow for the
increased wall thickness. The space for the added insulation can be
relatively slight, as when framed by 2x2s or 2x4s; larger amounts of
insulation can be added by strapping and crosshatching layers of wood
framing and putting the insulation within the framed spaces. The
largest amount of insulation can be added with the least framing by
use of a curtain wall. The purpose of a curtain wall is to hold the
insulation in place and to keep the rain off. The curtain wall is not
a structural wall since the inside wall holds up the roof. The siding
applied cannot be a heavy material -- wood, aluminum siding, and
stucco are suitable. A continuous vapor barrier can be installed when
insulation is added exteriorly.
4. A house with a brick façade is very difficult to insulate
exteriorly. A curtain wall must be attached to a load-bearing
structure of the wall, foundation, and/or roof. Thus the ledger plate
would have to be attached by lag bolts through the brick veneer into
the internal wood frame of the building or anchored into the concrete
foundation. This method is far more difficult than directly bolting
to the load-bearing members of a house with wood siding. An
alternative approach for insulating brick exteriors is to anchor foam
boards to the brick. This method, however, will not be able to
achieve very thick levels of insulation.

Procedure for retrofitting exteriorly (curtain wall)

1. Make the curtain wall studs of the proper length to extend from
the sill plate to the roof rafters. Determine the thickness of
insulation the curtain wall is to hold. Attach the proper length
horizontal 2x4 inch member with plywood gussets to provide for the
appropriate wall thickness.
2. Remove the existing siding if it is either rotten or to be
reused. Remove the soffit covers. Use a continuous polyethylene
vapor barrier to cover the wall. Seal all joints of the vapor barrier
with overlapping folded seams (French seams) and secure the seam to
the wall with furring strips. Acoustical sealant or other long-
lasting caulk should be used to improve the air/vapor seal around
window, doors and other breaks in the vapor barrier. Additionally,
secure the vapor barrier in place with wood strips to prevent future
leakage at these breaks in the vapor barrier. TenoArm film is
preferable as a vapor barrier. However, the widely available 4-mil or
6-mil polyethylene does an excellent job if properly sealed. The
vapor barrier must then be covered to protect it from wind damage, UV
light, and other damage that could occur during retrofitting. After
sealing the vapor barrier, it can be protected by covering it with a
radiant barrier, building paper, or sheathing material.

3. Attach a 2x4 inch ledger plate to the frame of the house, using
lag bolts. Install joist hangers to the ledger plate at the spacing
needed for the curtain wall studs (see diagrams), 24-inch spacing for
the curtain wall studs is usually sufficient.
4. The curtain wall studs are mounted by the joist hangers on the
bottom and securely attached to the roof rafter at the top. The sole
plate of the curtain wall connects all curtain wall studs. Building
paper, tarpaper, or equivalent under the siding will help keep the
rain out. The plywood bottom and the exterior siding provide
sheathing strength for the exterior curtain wall.
5. Retrofit the basement walls either exteriorly or interiorly (see
page 69). To retrofit basement walls exteriorly, it is necessary to
dig a trench wide and deep enough to attach the vapor barrier and
install the exterior foam insulation boards. (Contact local utilities
to determine where it is safe to dig, and rent a backhoe to save much
labor in digging.) The vapor barrier and foam boards, 3 inches or
more thick, are installed all the way to the footings. Extended
perimeter foam boards, 3 inches thick, are added up to 4 feet away
from the foundation, not covering the drain tiles near the footings.
In milder climates, 4-inch-thick foam boards are installed to a depth
of 2 ft below grade and as extended perimeter insulation about 4 feet
away from the building. Cover the foam boards above ground with a
protective barrier -- metal flashing, special plastic covers, pressure
treated plywood, or special stucco material designed to cover foam
insulation boards. See manufacturer listings after the references.
6. The floor over a crawl space is insulated by applying the
insulation for the full depth of the floor joists. The vapor barrier
should face upward toward the inside of the house. The insulation can
be kept in place between the floor joists by a number of methods. 1)
Hold the insulation in place with insulation support netting, a weave
of nylon fibers sold in rolls covering 1,000 square feet. 2)
Sheathing material is the most expensive way to hold up insulation,
but perhaps the most durable. 3) Hold the insulation up with stiff
wires wedged between the joists; wires are sold for this purpose. 4)
Crisscross wire from nails at the bottom of the joists. 5) Cover the
insulation with chicken wire. 6) Cover the outside of the insulation
with Tyvek® (or other brand) housewrap to hold the insulation in place
and to keep wind out of the insulation. 7) Cover the insulation with
a perforated radiant barrier; perforations are necessary to allow
moisture to escape. The insulation support netting is economical and
strong and could be modified to hold up an extra layer of insulation,
using little additional framing. By having 2x2s attached to the floor
joists, additional insulation can be fitted between the bottom of the
floor joists and the insulation support netting. The ground of the
crawl space should be covered with a plastic moisture barrier if
required by code or if the soil tends to be moist. This prevents the
crawl space moisture from dampening the insulation. Be sure to
insulate any ducts and water pipes in the unheated crawl space.
Alternatively, it is possible to cover the walls and ground of the
crawl space with insulation and a vapor barrier instead of insulating
the floor above.23, 41

See pages 147 to 153 for practical details on retrofitting insulation.


















Part Three
HOUSE VENTILATION
Fresh Air for Tightly
Constructed Homes

See 2nd half of book for continuation . . .