Will closed cell spray foam on rim joist interior be a vapor trap with 1″ XPS on exterior?
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We are in Southwest PA, climate zone 5. Right now, our house is going to have 1″ of XPS on the exterior walls, including rim joists to the basement. We are planning on spray foaming the basement with 2-3″ of closed cell foam, including the rim joist interior. 1″ of XPS is only average 1 Perm (range of 0.8-1.2), while the foam should be vapor impermeable. Is this going to cause the rim joists to rot due to inability to dry, or is the 1 Perm likely enough?
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