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Will vapor barrier paint on the ceilings prevent most of the air and moisture migration from the living space into the attic?

My house (currently being constructed in SW Colorado) will have Sheetrock walls and ceilings throughout. Will vapor barrier paint on the ceilings prevent most of the air and moisture migration from the living space into the attic?

There are several dropped ceiling soffits wrapped in sheetrock. If I paint these per above, and fill the inside cavity with the same blown-in insulation used throughout the attic (R60 cellulose), will I need to do any further sealing of the soffits?

Thanks for any help or suggestions!

Asked by Donald Bradley
Posted Sun, 11/18/2012 - 11:25
Edited Mon, 11/19/2012 - 06:01

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4 Answers

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Donald
Vapor barrier paint will do nothing to prevent air leakage into your insulation...it will only slow down the vapor flow. You should probably concentrate more on air leaks. I suspect that you have many can lights in your soffits? These are notoriosly leaky and very difficult to air seal. Best way to find leaks is to use a blower door...maybe hire a pro to help.

Answered by Garth Sproule 7B
Posted Sun, 11/18/2012 - 12:55

2.
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Thanks Garth. I tried to keep the recessed lights to a minimum, and they are all IC-AT cans.

I'm not sure my original post voices my main concern, which is actually minimizing warm air migration from the interior into the attic, where it might cause ice dams during Colorado's cold winters.

So my revised question is this: Shouldn't painted sheetrock walls and ceilings - in and of themselves - prevent many if not most warm air leakage issues from the interior into the attic?

Answered by Donald Bradley
Posted Sun, 11/18/2012 - 13:20

3.
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Donald
The sheetrock itself is indeed an excellent air barrier. However, it must be detailed properly to work well. Air can still leak where the sheetrock meets the bottom plate for example...this is where continuous gaskets or caulking is required. I suggest that you do a search on this site for "Airtight Drywall".

Here is an article about ice dams
http://www.buildingscience.com/documents/digests/bsd-135-ice-dams/?searc... drywall

And here is one detailing airtight drywall
http://www.buildingscience.com/documents/information-sheets/air-barriers... drywall

Answered by Garth Sproule 7B
Posted Sun, 11/18/2012 - 18:05

4.
Helpful? 0

Donald,
A lot of air can leak into an attic above partition walls that are nowhere near the exterior walls. Indoor air enters the stud bays near electrical outlets and then leaks into the attic through the crack between the partition drywall and the partition top plate.

So-called IC-AT recessed cans can leak a lot of air.

If these ideas are new to you, and I suspect they are, you should hire a professional with a blower door to help you with your air sealing.

Answered by Martin Holladay, GBA Advisor
Posted Mon, 11/19/2012 - 05:51

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