Insulating Rimjoist including deep cavity
Hello,
I live in Zone 5a in a 1910 house. I have been air sealing the rim joists by first spraying Great Stuff Foam around the rim joists. In a few places I could see the daylight come through. Next I’m putting 2″ styrofoam on the bottom and one vertically. Then I spray the Great Stuff Foam around the rigid foam again. I read the articles and Q&A and came to this approach. Let me know if I’m doing anything wrong.
My main question is in an area under the front portico, there is a cavity that is two or three feet. During winter, I can feel cold draft coming via this cavity. I can reach inside the cavity. So can I put rigidfoam with the cavity behind it? It would trap air behind it. So I suspect this would be a problem, but I’m not sure. I don’t know if this is related, but I get a lot of draft from under the front door, which is above this area.
Thanks.
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I forgot to explain the images.
The first picture shows the cavity on the right. The second picture is the rimjoist after first sealing before installing rigidfoam. Last picture shows how I finished it.
If you're getting a draft, that means air is circulating into the space. If you can't insulate inside the space, and air seal the ends/sides of it, the next best thing is probably going to be to insulate the next joist over and box off the inaccessible space with rigid foam. This means the inner joist is essentially "outside" the building envelope entirely, but the air draft you felt means it should have air movement to avoid moisture problems. The other joist you'll insulate to seal off the interior of the home.
I have a similar problem in one of my crawlspaces here, and the best I could do is what I described. I'd love to hear from anyone who has a way to actually insulate INSIDE one of these spaces! Even spray foam isn't a good option here, since there is no way to access most of the space.
Bill