Ice and Water Shield for housewrap?
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| Posted in GBA Pro Help on
I am building a new house in zone 4A. We are using 6″ studs and the interior insulation is a hybrid flash and batt configuration with 2″ ccsf and 4″ fiberglass. Exterior cladding is cedar shake shingles over a rain screen. My GC want to use Ice and Water Shield for the WRB because of the sealing properties from nail penetrations. I do not think it is a good idea, as I think the wall needs to be able to dry to the exterior, and the interior insulation is vapor impermeable. Any thoughts?
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Replies
Doc,
You are right. The c.c. foam is effectively a vapor barrier. You should not have two vapor barriers. Use Tyvek or similar to allow your sheathing to dry to the outside. The rain screen will provide the drying capacity to deal with any moisture penetration around the nails.
Cedar shingles are about the most forgiving cladding you can install--it is really hard to trap moisture behind them. There is absolutely no reason to put I&WS over the sheathing, and very good reasons NOT to do so. When I hear GCs recommending stuff like that, I wonder if they have had problems due to flashing mistakes that they didn't understand. I would install 15# felt with a 50% overlap, the rainscreen, and the shingles.