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Great_North 02-08-2014 06:53 PM

Insulating Rim Joist Question
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I have a question about insulating the rim joist in my basement ceiling. House is only 8 years old and weíre plugging away on finishing the basement and are at the ceiling now. I plan on just adding fiberglass rolls/batts between the joists and have had non-faced fiberglass in the rim area (see photos) since new without any issues. Before I do anything else, I want to know if fiberglass in the rim area is sufficient or is there a better way? Iím thinking spray foam would be better but cost is a factor as always. I just want to do this once and donít want to have to worry about it again 5, 10, 20 years down the road so I want to make sure I do it right. Foundation walls are poured and we live in the northern Midwest and have very cold winters, below zero air temps are very common.

Also in using the fiberglass rolls/batts between the joists Iím assuming unfaced friction fit would be fine? Or would I want kraft faced?

Thanks for any help or feedback!

kok328 02-08-2014 09:03 PM

I believe, per fire code you have to use unfaced.
Friction fit is ideal as compressed insulation has less rated R-value.

Curious as to how you finished your walls (vapor barrier, insulation, furring strips, etc...)

Great_North 02-09-2014 07:08 AM

Thanks kok. Do you mean for the rim joist areas on the ends of the joists or for the entire joist? Walls are poured with studs attached and insulated with unfaced fiberglass then the drywall. A 4mm plastic vapor barrier is installed on the subgrade portion extending 12" (I think) above grade between the drywall and insulation/studs. No vapor barrier is install on the above grade portion other than the first 12".

kok328 02-09-2014 12:25 PM

any exposed insulation has to be unfaced

Great_North 02-10-2014 10:12 AM

Thanks. As far as material between the joists for more noise reduction throughout the entire ceiling what would you recommend? I can get a bunch of R30 12" thick unfaced rolls from a buddy for almost nothing so was thinking of using that...? Thanks.

nealtw 02-10-2014 10:58 AM

Depending on code where you live, where I am the vabout barrier would go from the floor to the floor above btween the floor joist and seal with accustic sealer any and all edges.
The r30 for the ceiling should work fine.

Great_North 02-12-2014 10:19 AM

Thank you!

nealtw 02-12-2014 10:29 AM

Before you hide that insulation at the rim joist, check it for dirt. Dirty insulation is a sign of air leaking, find any holes and caulk them, fire rated caulk.

Great_North 02-13-2014 11:20 AM

Will do. Thank you!

drewdin 04-03-2014 10:27 AM

when do you need a vapor barrier in the basement ceiling? I plan on insulating my basement ceiling also, the kitchen is above. The basement is not finished, would i still need a vapor barrier against the subfloor above? I didn't plan on using one, thx

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