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Vapor barrier under stairwell to main floor fromi garage

Vapor barrier under stairwell to main floor fromi garage


Old 03-17-12, 12:20 AM
Thread Starter
Join Date: Mar 2012
Location: United States
Posts: 27
Vapor barrier under stairwell to main floor fromi garage


This is 1992 built home in rainy Seattle which has an unfinished garage/basement.

I opened up the drywall under this stairwell for extra storage. The stairwell is part of the heated main house, and underneath we're in the unheated garage. I'm going to add R30 insulation and then 5/8" fire code sheetrock. I'm pretty sure I need a vapor barrier. I read elsewhere that you normally put the vapor barrier first to the warm side of the insulation. So would I staple the vapor barrier to the underside of that staircase, and then add the fiberglass insulation followed by drywall? or should the insulation go first, then vapor barrier and then drywall?

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Old 04-14-12, 02:42 PM
Join Date: Apr 2012
Posts: 64
The vapour barrier should always go on the warm side of the insulation. This is to ensure that you do not get interstitial condensation within the insulation, which would render it useless and also increase the possibility of rot. In your case, the vapour barrier would be stapled to the u/side of the stairs (remember to tape any joints), then insulation, then fire-resisting board.

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