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Basement wall insulation: Is spray foam + Roxul good?

wolverine72 | Posted in General Questions on

I’m in the middle of a basement retrofit for half my basement (live in the NE in zone 5 near zone 4). The stud walls were already in place (previous owner) and I didn’t want to rebuild it all so I stripped everything down to the studs. Found fiberglass and cheap styrofoam (joints not sealed) behind the sheetrock. Don’t have moisture problems, but I’m glad that’s gone as that was a problem waiting to happen. Especially since part of the foundation is cinderblock and part is uneven stone (120 years old).

With the studs in place and the varied stone depth, I ruled out using xps (there’d be too many air gaps behind it). So I’ve spray foamed the entire foundation, from floor to up and over into the rim joists. At least 1″ but more like 1.5″-2″+ everywhere. It’s already made a noticeable difference just stopping air leakage. In one section where the studs were 1″ from the block the spray foam comes out into the stud bay. In other sections there’s 6-8″ behind the studs. The plan now is to add Roxul into all of the stud bays to get the R-value up to something like R-25. I’ve read a number of posts on here and I believe Martin has said that should be an ok method. The foam seals and provides a somewhat impermeable layer before putting in the Roxul.

Is it ok that the Roxul will be touching the spray foam in some sections but have an air space behind it in others? I believe so since the spray foam stops the air flow, but wanted to confirm.


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  1. GBA Editor
    Martin Holladay | | #1

    Your plan sounds fine to me.

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