My question is around the use of foamboards in finished basements to serve as a vapor retarder and to reduce condensation.

I've already fastened foam boards against all the concrete walls, taping the seams, and also cutting pieces for the sill boxes.

But what do you do on the sides of the house that don't have sill boxes (see picture below)? Currently the foam boards end as high as I could go, but its impossible to get behind that joist. There is actually fiberglass stuffed behind it but it would be hard to pull out. Should I put foam boards against the face of that last visible joist? Caulk the gaps? Any help would be appreciated.

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  • I should also note that originally we were going to spray foam. That's why we framed before putting these foam boards up. It makes things much more of a pain.
    – ademartini
    Commented Nov 5, 2018 at 14:30

1 Answer 1


Closed cell foam is an insulator and vapor barrier in one.

You can buy a kit at the blue box store that contains the two parts that get mixed together with the enclosed spray tip.

I have used this one (Available at the blue box store ). but this one looks good also.

You could do all of your gaps and hard to reach places.

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