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Old 12-15-2011, 11:54 PM   #1
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flat roof construction.

Hi all. Building a flat roof -2.5% slope. The plans call for an air space between the insulation and the ply. Question....if I go with spray foam -2 lb...does the air barrier become irrelevant?
Do building codes allow for this compromise ?

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Old 12-15-2011, 11:56 PM   #2
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flat roof construction.

I believe that if it is closed cell spray foam, not open, you are correct because it will be an air/vapor barrier. Check on buildingscience.com or greenbuildingadvisor.com

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Old 12-16-2011, 12:26 AM   #3
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flat roof construction.

Yes, the International Residential Code does allow for some non-vented attic conditions like you are talking about.

I know it is a flat roof, cathedral type ceiling is not an attic area, but the code calls it that.

There are specific conditions that have to met though.

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