I am looking into two methods of insulating my rim joist space in the basement on a house in Zone 5. I realize that spray foam kits are the cat's meow in air sealing and possibly ease of use - but their price is insane. The other option I am looking at is cutting 2" thick XPS to fit, then foaming the edges to seal.

I have 141 sq ft of rim joist to cover, this does not subtract the I-Joist in that area. I would want at least 2" thick of spray foam, and all the kits I see come in 200 sq ft or 600. Well, I conveniently (not) need 282 sq ft. So I am looking at the 600 sq ft kits. There are some leading brands out there but the only one I think I am comfortable with is the Foam It Green product that actually turns a green tint when the foam is cured properly so that I know the mixture is just right. To me it looks like an extra $50 to $100 for peace of mind. However, the kit is $765 right now.

A sheet of 2" XPS is only $33 or $30 when on sale. Math says (with waste) that I would need 5 sheets, so about $160 then spray can foam would easily run $40.

For about 1/3rd of the cost I would have the same results. It would just be more time. Looking for some suggestions on how else to weigh the cost of the spray foam. And is the 'turning green tint' just a sales gimmick and nothing to be interested in? Is there a better way to go about doing this?

  • So buy two 200 sq ft kits, or buy a 200 dq ft kit, and do 82 sq ft with foam. At the end of the day, foam is foam, and the difference as youve noted/implied is TIME & coverage area (spray foam can seal gaps.....) – noybman Jan 20 at 15:47

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