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Old 07-29-2012, 11:11 AM   #1
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is unfaced fiberglass bad in basement rim joists?


We recently moved into a 32 year old house. The rim joists in the basement are insulated with unfaced fiberglass bats. It looks sloppy, like scrap pieces were just thrown in. I want to remove the old insulation and put new in. I know that most like to use the foam board and seal/caulk the edges. This would take me forever....especially with the hvac and electrical running thru. I have seen no evidence of moisture problems. Can I just take out the old and add new(and more)? If I fill up the whole cavity, will I have to worry about moisture problems? So far, I have done one area. I used the pink, unfaced R-30. I was able to fit about 3 pieces of it in the cavities. Am I overinsulating....or is it not possible to over do it in this area?

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Old 07-29-2012, 12:10 PM   #2
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is unfaced fiberglass bad in basement rim joists?


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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Old 07-29-2012, 12:42 PM   #3
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is unfaced fiberglass bad in basement rim joists?


+1

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

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Old 07-29-2012, 01:33 PM   #4
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is unfaced fiberglass bad in basement rim joists?


i'd second the spray foam. its expensive, but cheaper than my time by far for when I did mine.
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Old 07-29-2012, 02:48 PM   #5
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is unfaced fiberglass bad in basement rim joists?


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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Old 07-29-2012, 04:00 PM   #6
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is unfaced fiberglass bad in basement rim joists?


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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Old 08-03-2012, 12:53 AM   #7
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is unfaced fiberglass bad in basement rim joists?


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/docum...l_seal_rev.pdf

http://www.buildingscience.com/docum...r-penetrations

Gary

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