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Community and Q&A

Rim Joist Insulation

leeken | Posted in GBA Pro Help on

I live in northern Iowa (Zone 6). I am finishing my basement. I have insulated the rim joists with 4 inches of XPS foam board sealed around the edges with Great Stuff spray foam. Previously the rim joist areas were insulated with fiberglass batt insulation. I removed the fiberglass insulation before installing the 4 inches of foam board. I am thinking of utilizing the fiberglass batt insulation by putting it over the 4 inch foam board insulation and wonder if there is any benefit or concerns with doing that. The spray foam used to seal the edges of the foamboard has expended beyond the face of the foamboard. If I put the fiberglass batt insulation over the 4 inch foamboard,  can the fiberglass batt insulation be placed over the excess spray foam or does the excess spray foam need to be trimmed off before placing the fiberglass batt insulation?

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  1. Will R | | #1

    Per Martin's article, batt on top of >2inch of rigid foam sealed with spray foam is acceptable. I'm guessing that trimming the spray foam has little impact.

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