Insulating Recessed Rim Joist

matt151617

I'm trying to insulate my rim joist. On the sides that are at the end of the joists, it is easy to slap up some foam board. However, on the side that parallels the joists, the rim joist is recessed behind the edge of the foundation. There is maybe a half inch gap for me to access it. Could I fill this with great stuff foam? Or just stuff it with fiberglass?

jklingel

Stuffed-in fg will be useless; fg batting is not good material to start with. I'd go w/ spray foam everywhere you can apply the rigid. Be sure to tape/goo the edges of the rigid to air seal.

matt151617

So it's as simple as filling that gap with lots of great stuff?

jklingel

BTW: It should say "CAN'T apply the rigid", above. If you can ensure that air does not sneak in past the foam, I see no reason why this is any different than applying foam anywhere else. Even a layer of foam at the gap,to plug the area up, will give you a large dead air space, which is better than nothing. But, you have to make sure you air seal real well, either way. It's too bad this was not insulated as it was built and access was available.

Gary in WA

That first joist is compromised anyway... What is above it on the floor- refrigerator, etc.?

Gary

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