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Re: Exterior Foam Sheathing over TyvekFrom: info@builderswebsource.com
Category: Alternative Building Techniques
Remote Name: 63.198.181.43
Date: 29 Mar 2002
Time: 10:33 PM
CommentsGenerally, Tyvek HomeWrap should be applied over any foam-insulated sheathing or building exterior envelope, not the other way around. Although Tyvek helps to reduce moisture infiltration, Tyvek is breathable with a high perm rating. Keep in mind that your proposed addition of 1/2" foam insulation will only add, at best, 1.5-2 "R" rating increase (assuming EPS foam). This slight improvement will be swamped by infiltration through doors and windows. The Tyvek itself also helps to reduce air infiltration, which by itself will improve energy efficiency. Furthermore, even if you use R-15 in the 2x4 walls, the actual performance of this may be slightly less in such a tight cavity. Our recommendation is to skip the use of the foam insulation given that your Tyvek is already installed over the exterior sheathing. You would have been better of building out of 2x6 studs, using R-19 or greater insulation in the first place, but we'll have to leave that for your next remodel! Builders Websource.
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