2 in vs 2x 1 in exterior EPS
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I’m in zone 5 and adding 2 inches of EPS over a vapor permeable housewrap (vycor env-s). I’m planning to use unfaced EPS (still working on sourcing it though). Is there any advantage to using two 1 inch layers of foam with the seams lapped, or should I just use a single 2in layer for a quicker install?
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Replies
Two layers with seams staggered helps to eliminate "3D air pathways", which is fancy way to say air leaks that cancel out some of your insulating efforts. There is an informative article about this that is written in a funny way (documenting "professional embarassement", in the author's words) over on Building Science's website.
You're fine using a single thicker layer with seams taped though. I've thought about injecting canned foams into the seams just before taping them to bond the sheets together, but I don't really have any hard data to definetively show if that's really worth doing or not.
Bill