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Old 02-11-2011, 10:19 AM   #16
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Would "Great Stuff" or equivalent be ok for insulating rim joists?


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Originally Posted by atxjoe View Post
I can't tell from your description if this would be an issue, but here's my concern: If you create a sealed air pocket where moisture can't escape you may have a mold problem. I was considering insulating under my floor by sealing rigid foam panels between the joists, using great stuff as the adhesive as described here. But that would create a warm, moist, air pocket under the floor and where I live almost certainly breed mold.
I decided instead to use spray foam which will adhere to the subfloor and prevent any mold growth.
I was thinking this but from my understanding the foam is not 100% air tight. It will let air through very slowly so it should not get moist behind there. Someone correct me if I'm wrong on this.

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Old 02-13-2011, 08:25 AM   #17
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Would "Great Stuff" or equivalent be ok for insulating rim joists?


I used polyisocyanurate, with caulk around the edges, then fiberglass batts. Works well. easy to cut in the parking lot also.
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Old 02-13-2011, 11:03 AM   #18
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Would "Great Stuff" or equivalent be ok for insulating rim joists?


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Originally Posted by Red Squirrel View Post
I was thinking this but from my understanding the foam is not 100% air tight. It will let air through very slowly so it should not get moist behind there. Someone correct me if I'm wrong on this.
My recollection from reading the buildingscience.com articles was that rigid foam works as an air barrier but not a vapor barrier, so it's good for putting on the outside. I think it explains in the "perfect wall" article.

http://www.buildingscience.com/docum...e-perfect-wall
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Old 02-13-2011, 11:13 AM   #19
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Would "Great Stuff" or equivalent be ok for insulating rim joists?


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My recollection from reading the buildingscience.com articles was that rigid foam works as an air barrier but not a vapor barrier, so it's good for putting on the outside. I think it explains in the "perfect wall" article.

http://www.buildingscience.com/docum...e-perfect-wall
I used the 2" foil faced polyisocyanurate boards at the rim joists with no trapped moisture issues. I checked 4 of them, 2 in the unheated crawl space.
Ron

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