Closed-cell vs. open-cell foam for insulating mudsill/rim joist
I’ve been working with a spray foam contractor to insulate the mudsill / rim joist area on the top of our 1890’s home in Boston (climate zone 5a). The house has a fieldstone foundation, with large beams (directly contacting the foundation) that serve as both mudsill and rim joist. We have the typical high humidity in the basement as one would expect. At this point the basement is unfinished, although we have a vision to finish it at some point in the future.
The contractor recommends open cell foam (8 inches depth for R-30), and while he understands the value of closed cell in preventing winter condensation, he says that the depth of the open cell would suffice as a vapor retarder. Is that a reasonable proposition, or should I be pushing for the use of closed cell?
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