odd rimjoist/floor joist, do I insulate
I’ve read if floor joists are embedded in concrete, it is better not to insulate the joist area to help prevent the joist ends from rotting (condensation on cold joists maybe?)
I’m not sure if I would qualify my joists as embedded or not. There is a rim joist at the outside edge of the foundation. The joists are attached with joist hangers. At the inside edge of the foundation, there was blocking installed. The foundation seems to have been poured through this void, into the forms. I can’t take the blocking out, since my subfloor ends on this blocking(boards run on the diagonal). The exterior wall sits on the rim joist.
Should I insulate this area or would that be asking for trouble?
The pictures are where the blocking has been removed.
I am in a pretty dry climate. No need for AC in the summer.
Adam
Edited 10/24/2009 1:13 am ET by Muteability
Replies
bump
Tough one. I would seal any joints with caulking or canned foam, then I'd probably go with something that could be removed for inspection when needed, like a thick batt of Roxul (mineral wool) or fiberglass. Normally sealing it up tight with rigid foam is the best approach but those encased joists make me nervous....
There were FG batts stuffed in to some of the cavities above a finished wall and there was a lot of evidence of air movement. The fiberglass was just acting like a big air filter. No vapor barrier. In the part of the basement with finished walls the stud wall is about 2" out from the concrete, so I can install about 5" of FG and vapor barrier between the joists and floor, flush with the inside face of the wall.The exterior is stucco, 24" eaves, foundation is minimum 2 feet above grade. There was no caulking around the windows and doors, I've added that so that should help with air leaks.In the unfinished section I can at least seal the joints with foam and see if the wood ends up feeling damp from any condensation.It is a pretty dry climate.
Edited 10/28/2009 12:53 pm ET by Muteability
Been pondering this. This sounds like largely a typical joists on conc foundation w/ a rim joist perimeter. No idea why they used joist hangers. The odd part is that the subfloor stops before the wall framing and the wall framing is on the joists. Your foundation wall sounds well above grade. So, normal is to insulate the rim. Also normal is to run your vapor retarder up the inner blocking to the subfloor above. No real reason why there would be moisture being trapped in the rim area. Being low in the house, my guess is that the air flow is generally inward, not out. But wind pressure can change that. Also being in a dry climate, I wouldn't worry too much about it, either.
Edited 11/3/2009 9:30 am ET by Clewless1
Thanks for the pondering. It's good to see you're thinking along the same lines as I am. It's great to have this community to ask the weird questions. Of course, it's easier to swallow when people opinions match yours.