EPS foam for unvented cathedral ceiling
Hi. I recently framed my roof with 2x12s for a cathedral ceiling. It’s a simple house, 20’x36′ footprint with a loft. We have no eves in the design, partially so I could get a continuous moisture barrier and aesthetic. The exterior walls are a double 2×4 wall.
So, for the ceiling I’m probably going to do 4″ of closed cell spray foam with batts or BIBs. However, I was thinking about getting EPS foam from a SIP supplier cut to my dimensions and therefore easy to install (roughly 25% of the cost of spray foam and no off gassing). Is EPS (10″ thick) vapor permeable and would I therefore need a layer of XPS foam with edges/joints sealed?
I’d like to go with the EPS if it performs correctly.
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