What is the current thinking concerning insulating rim joists? I’m in Massachusetts and have had a home energy audit. One of the suggestions was to insulate the basement rim joist with polyiso.
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what I did based on what I learned from here/other FHB resources
> Preliminary imperative: if you're using cans, get a roll of vinyl tubing, cut about a 12-18" length, put on end of the plastic tube that comes with the can, and it will make it much easier to apply. Also, where goggles (!) and wear a long sleeve shirt or sweatshirt that you don't mind trashing, and a hat, and put down a tarp. I am meticulous, and went into this with the best of intentions, and I got this crud all over, including in my hair.
>sprayfoam the perimeter of the rim joist cavity
>put in XPS against the rim joist vertically (have a bunch handy that are already cut to size (you can use EPS or polyiso, read different things about the merits of each))
>sprayfoam around the edges, and then put in another layer of foam board
>sprayfoam around the (remaining) perimeter of the sill and then place foam board flat (on some, I did the flat part first, and then the vertical in the "back" of the joist cavity, and didn't find much difference, so you can do either one first).
>Finish by filling the remaining cavity with Roxul (mineral wool insulation that is fireproof).
If I had obstacles (wires/pipes/vents, etc.) I either just filled the smaller cavities with spray foam, or I
This made a MASSIVE difference in our (at that point) unfinished basement.
Thank You for your detailed response. Fortunately, my utility company has an energy conservation program and will pay for about 75% of the cost of the product and installation. Other than having all the fun that you had doing it the only thing that I have to do is clear a path around the perimeter of the basement so that the contractor can easily reach the rim joist. Will all the stuff that I have in the basement I'm not looking forward to this.....but the heat saving will be nice.
what I learned
What I learned on here was as much about air sealing as insulation, so the spray foam (or caulk) is as important as the insulation itself. Tiny cracks around the edges of the foam will transmit a lot of cold/warm air, unless it's sealed.
I just redid my rims with 4" of XPS, two 2" layers.
Friction fit. A bit of detailing was required since I have TJIs, I ripped the sheets to width on the table saw, used a sharpened putty knife to cut them to length, then used a multi tool to make little cutouts for the flanges. It went surprisingly fast, and the things are in there tight as a friggin drum.
160' of rim, took ten 2" thick sheets to a get 4" thickness around the rim.