My house has very small rim joists spaces in the basement.

I have noticed that the floors are cold, as are the walls. So I want to take action and this is where I thought to start.

My problem is that the space is maybe only 2" and quite deep, which is going to be very difficult to do the traditional way (using foam board and spray foam).

Should I buy some insulating spray foam and just seal the cavities? As far I know this is fine as long as it is air tight to prevent mold and such.

Any information would be super helpful! I included a picture, although it is not easy to see what's going on.

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Yep, spray foam is the ticket. The conventional stuff expands greatly, so go easy until you get a feel for final volume. You'll end up using way too much and having a mess otherwise. You can certainly do it in layers.

Be aware that open cans can't be stored for longer than a few hours or so. They cure up and quit working. Don't start a can unless you'll finish it, or at least most of it.

Also note that urethane does not come off skin, clothing, and other objects. Protect yourself and your property before starting to spray.

  • Awesome, thanks. Would something like this be ideal? Or perhaps just buying cans of Great Stuff? homedepot.ca/product/… – Shinobii Dec 1 '20 at 21:01
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    For your small-ish project a half-dozen cans of red can Great Stuff would maybe be more economical and practical. No cleanup. – isherwood Dec 1 '20 at 21:03
  • If I may be so bold, should I aim to fill this space flush with the concrete? It's about 6-8 inches deep. – Shinobii Dec 1 '20 at 21:05
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    Consider your walls' R-value when making that call, but I don't see why not. You might leave it back just slightly for a cleaner appearance. You can also slice it off with a knife or saw after curing for an hour. – isherwood Dec 1 '20 at 21:07
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    Perfect, thanks for all the information. I will (in the future) be applying foam board to the entire basement. I still have some research to do in terms of framing, but I assume I will end up beefing up the insulation at that point. In any case, thanks! – Shinobii Dec 1 '20 at 21:09

Conventional insulation can be used, but Tough Stuff really gets the job done right. If you overspray, it is easy to trim with a sheetrock knife. However, you have to wait a day or two until it expands and dries. Definitely, try not to overspray.

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