# rim joist insulation?



## s002wjh (Dec 23, 2011)

my basement concrete wall is around 60f, but the rim joist area/header is around 50f. the rim already has fiberglass bat, so i'm not sure i need redo the insulation or not. outside is around 32f


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## joecaption (Nov 30, 2011)

There has to be at least few hundred post on this one subject.
Tried the search funtion?
Fiberglass does not block air floor and will just end up causing mold.
Need 2" foam and spray expanding foam to seal the gaps.


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## Windows on Wash (Aug 30, 2011)

Good read.

https://buildingscience.com/documents/information-sheets/critical-seal-spray-foam-at-rim-joist


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## s002wjh (Dec 23, 2011)

ok what rigid foam/board i should use on rim joist. also what caulk i can use on the seam/gap of board.


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## Dave Sal (Dec 20, 2012)

I used Owens Corning R10 rigid foam board. Was about $18 per 4'x8' sheet about 5 years ago. I think I used silicone caulk to seal the edges (the attached pic doesn't show the silicone sealing of the edges). In addition to insulating the rim joists I closed off and sealed the two outside air vents. The crawlspace now stays about 63 degrees all year long. It used to get close to freezing during the winter.


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