OT home improvement question - condensation

[GaryH82012]

With all the knowledge in this group, this should be an easy question: I have a
wood framed, aluminum roofed patio cover attached to my house with the
underside of the aluminum exposed and badly painted. There is always a great
deal of condensation on the underside on damp cold nights, resulting in all the
paint on the wood framing being blackened with mildew and the paint badly
peeling. Sometimes it's like it's raining under there. I need to clean this up
and eliminate the conditions causing the problem. The way I see it, the
condensation is due to the aluminum's high degree of temperature conductivity.
The cold air on the top side of the aluminum is chilling it so that the warmer
air on the underside which is trapped there causes the condensation. One
solution may be to use fiberglass panels instead, but all the products I've
seen are kind of ugly and cheap. Another might be to put some insulation under
the aluminum and nail plywood sheathing to the underside of the framing to
create a barrier between the warm and cold air, eliminating the condensation (
I think) and saving me the trouble of prepping and painting all the wood
framing. Another might be some of that steel roofing, or even aluminum, with a
layer of plywood under it. The old panels have some leaks and should probably
be replaced in any case. The roof has a very low pitch, so I think any kind of
sheating and shingles are out. Can anyone suggest a solution? Thanks for
reading, Gary Hastings

[Jack Hayes]

If you go with fiberglass insulation be sure to install a good vapor barrier on the
warm (inside) side of the insulation, 4 mil poly would do a good job. Make sure it
is well overlapped or sealed at any joints. Also the area above the insulation must
be vented to the outside.

JACK

[malcolm.scott]

I wonder if you install some louvre type ventilation openings at the top to
improve airflow.
Malcolm

"GaryH82012" <garyh...@aol.com> wrote in message
news:20010313021648...@ng-fq1.aol.com...

[J R North]

The solution is in your post. The warm air is trapped in the
patio . Ventilating the enclosed area might help.
JR
Dweller in the cellar

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[GaryH82012]

>
>The solution is in your post. The warm air is trapped in the
>patio . Ventilating the enclosed area might help.
>JR
>Dweller in the cellar
>

But the area is not enclosed. On two sides it abuts the house and garage, but
on the other 2 sides it is wide open with plenty of air circulation. Gary

[Nick Hull]

In article <20010313230853...@ng-fs1.aol.com>,
garyh...@aol.com (GaryH82012) wrote:

I have the same dripping problem with a equipment shed that is just a
roof, no sides at all. Terrible dripping from condensation. Try
installing a fan to gently circulate the air and blow away the
condensation before it drips. Sort of like the fan old timers used to
mount on the dashboard to defrost the windshield, it will work without
heat.

Other than that, maybe you could install thin styrofoam sheets under the
metal, or spray some sort of insulation.

--

Committees of Correspondence Web page:
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[Mel Heggie]

Jack Hayes solution is a possible answer to this problem. The
condensation
happens, because, at night, the sky is a radiant heat sink. It causes
heat to be
radiated from all warmer surfaces. The aluminum roof could be 5
degrees
colder than the surrounding still air. You could attach a thermometer
to the
aluminum roof and measure this.
As the roof is now, on a damp night, below the dewpoint of the
air,
moisture will condense on both the top and the underside.
You may be successful at trying to stop moisture migration to the
underside of the roof with a vapor barrier on the underside. Note this
will
be difficult as all joints would have to be sealed, even the overlaps
and nail holes on the roof. The joints would eventually fail and
moisture would get in.
In my opinion, the solution is to think of a way to keep the roof
from
getting as cold as the dewpoint of the ambient air.
A solution which may work is to put a layer of waterproof
insulation
on top of the aluminum roof (such as 1 inch of styrofoam) and another
layer of roofing on top (to protect the insulation) with an inch of
air space.
The moisture may still condense on the underside of the new top roof
but will be contained between the insulation and your existing roof.
It
will either run out over the eave or re-evaporate during warmer days.

Mel(back to lurking) Heggie

"Jack Hayes" <at...@cyberbeach.net> wrote in message
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