# is unfaced fiberglass bad in basement rim joists?



## gregzoll (Dec 25, 2006)

Unfaced would allow it to breath. If you want to take it a step further, use TigerFoam to seal the bays.

I just used Kraft faced R-13, because I did not want to totally air seal the basement, just wanted to stop cold/hot air convection currents.


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## Windows on Wash (Aug 30, 2011)

+1

Spray foam it. That will be faster than cutting and stuffing those pieces in.


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## bbo (Feb 28, 2010)

i'd second the spray foam. its expensive, but cheaper than my time by far for when I did mine.


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## ANDYK. (Jul 29, 2012)

Thanks for the replies. I've already started w/ the fiberglass.... Just wondering if multiple layers of r-30 unfaced will cause any moisture issues??? I'm fine with overkill, I just dont want to cause any problems.


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## gregzoll (Dec 25, 2006)

One layer is all you need. No need for overkill. Update with your location, so that people can better help you. Do suggest going over the info at buildingscience.com, which explains the whole process of making the structure work as a whole.


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## Gary in WA (Mar 11, 2009)

If you are in a heating climate, air seal them from the basement. Fiberglass is air permeable, fine after you install foamboard and canned foam the edges. The idea is to stop infiltrating/exfiltrating air from happening. It does not want to breathe. The rim board expands/contracts with the seasons, letting un/conditioned air right through it. At least use faced toward the warm inside.http://www.buildingscience.com/docu...joist/files/bscinfo_408_critical_seal_rev.pdf

http://www.buildingscience.com/documents/information-sheets/sealing-air-barrier-penetrations

Gary


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