Passive House Types in California

[George J. Nesbitt]

The predominant type of house in the Bay area (especially older
neighborhoods) is;
Wood frame, platform & balloon framing.
Crawlspace, vented
Attic, vented.
Floor furnace or furnace & ducts in crawlspace
Wood & stucco
wood & asphalt roofing

Mid century on;
Wood frame, platform
Slab
Attic or roof
Furnace in closet, garage, or attic, with ducts in attic
stucco
wood & asphalt roofing

And there are many variations;
Floor; slab, basement, unvented crawlspace, vented crawlspace,
exterior floor (no basement or crawlspace).
Furnace; floor, wall, basement, crawlspace, exterior vented closet,
interior venting closet, attic.
Ducts, none (direct vented or not, gravity or fan), crawlspace, attic,
roof, conditioned space.
Ceiling; attic un or underventilated, attic ventilated, no attic
(roof) ventilated, roof unventilated.

And we could go on.....

[Dan Johnson]

Thinking about George's building types....
I have a remodel project that is an early 1900s house over a
crawlspace, two stories with an attic. It has hydronic baseboard
heat. We'll be replacing the siding and the roof, so we have
opportunities to airseal here using the new sheathing (beneath new
siding/roofing). The climate is Healdsburg (Sonoma County) and the
occupancy is two adults with family gatherings on summer weekends.

The conditions I'm describing would apply to nearly every old,
wood-framed Bay Area house with a crawlspace, attic, and wood siding.
I'd like to use this project to tackle this building type as a PH
retrofit prototype.

I'm imagining that we'll blow cellulose into the stud bays from the
exterior (full 2" x 4" studs, 21" on center) and add several inches of
rigid foam or rockwool insulation over the new sheathing.

The part that's troubling me is the crawlspace. It's too small for
access to airseal and insulate the floor itself from underneath, or to
really even tackle the cripple wall from the interior. I'm wondering
if we can excavate to the footings (from the outside) and airseal &
insulate the cripple wall from the outside using maybe rigid foam?
We'll still need someone to wiggle into the crawlspace to install a
vapor barrier against the ground.

Maybe we keep the hydronic baseboards, supply them with a Solar
Phoenix water heater (at lower temp than their design temp). Retrofit
the Recoupaerator ERV in the conditioned attic with minimal ductwork,
just vertical risers through closets to the ground floor rooms. We'll
only need 80 CFM (plus boosting for showering), since the ERV airflow
is not heating the house in winter.

I haven't run it in PHPP, so I'm not sure what's required yet. I think
if we can get the airtightness with new sheathing and windows, then we
can vary the exterior insulation to make the PHPP calc out.

Any ideas on the crawlspace? Thanks, --Dan

[bronwynb]

Dan - Your Sonoma project may be a good candidate for experimenting
with what the Passive-On group of builders/designers for the warmer,
mediterranean climates, are doing. There has been some mention of not
insulating under the slab/sub-floor and using the earth to assist with
passive cooling in the hot summer months. You may be OK sealing the
dirt with a moisture-barrier and only doing the exterior perimiter
insulation you mentioned. (?) Not sure if the current PHPP will be
able to help you here just yet, but check out this presentation, which
is what I'm basing my crazy speculation on:
http://www.slideshare.net/sustenergy/passive-home-training-module-for-architects-and-planners
More info here too: http://www.passive-on.org/en/index.php
Sorry to give you more research to do!

> > And we could go on.....- Hide quoted text -
>
> - Show quoted text -

[George J. Nesbitt]

A full exterior retrofit will be the easiest way to get to PH Standards (too bad we can't get an answer on relaxed standards for retrofits).

Rather than insulating the 2x4's why not just exsulate? Leave the 2x4's free of insulation and but all the "insulation" to the exterior exterior by building double walls or using rigid. This way the structural frame is within the interior environment, stable, and dry, easy to access for any changes. The new structural sheathing becomes the interior air barrier, with possibly an exterior one too.

I am thinking of using rigid rockwool for exterior insulation on my house over the stucco! I need to research the product more, and the question on exterior cladding, and attachment are some unanswered questions.

The crawlspace should probably be dug out a bit (18" minimum code), which would make air sealing and vapor barrier installation. Everything else should be done from the outside with the rest. The question becomes do you insulate the floor, or the dirt, or neither. It will take running some numbers to see the +/- of the various strategies.

What about roof insulation, and windows, (save the 100 year old windows).

This should be a fairly easy retrofit to do to PH

[Babette Jee]

If you do an exterior retrofit, i.e. adding insulation to the outside, can you still maintain

the required or legal distance to the property line?

Some of these older houses have minimum distances to property line already and making the house "grow"

would mean fire rating, no openings or not allowed.

When do the new construction rules kick in? Current requirements for distances to property line rules, 

are usually  greater than the existing distances in older neighborhoods.

When does minor work become major and new construction rules kick in?

Babette  

[Graham Irwin]

Why would you not also insulate the existing exterior walls? If you're covering the exterior anyhow, the holes you drill for cellulose won't be a big deal and you can use a lot less exterior foam if you add that cellulose, it's probably work ~2" of foam, correct? Plus, substituting shredded recycled paper for petrochemical foam blown with global warming gasses is always a nice touch!!! ;-)

I am ambivalent about "conditioned" crawlspaces for Passive Houses. To my understanding, you basically wind up heating and/or cooling a "basement" with no insulation on the floor. I do not buy the argument that the Summer cooling effect balances Winter heat loss (look at CA energy end uses, Residential AC doesn't even come close to the PH limit.) It would have to be calculated, but it may well be that the optimal solution is something along the lines of Joe Lsitburek's detail for a flood zone crawlspace:

If you want Summer ground tempering, I would suggest a thermostatically controlled pump, circulating glycol through a ground loop and a hydronic duct coil at the inlet to the HRV - this way, you also get Winter tempering too!!! (Whenever the air is below ground temp in heating mode and above ground temp in cooling mode, this will give you benefits.) Cheap too...

It's time to migrate these discussions to the PHCa website!

Graham Irwin

AIBD, CPBD, CGBP

Remodel Guidance

415-258-4501

Residential Design  •  Plans & Permits  •  Green Building  •  Period Homes

 

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