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I'm removing old wood paneling and drywall which is glued to (what appears to be regular Styrofoam) foam board, which is glued to a cinder block basement wall. The goal is to add more insulation (2x4 framing + rockwool) to the existing foam board (R10 -> R24).

The issue is that pulling the drywall down is ripping chunks out of the existing foam board - up to 1/2" deep so far - I was hoping to leave in place. The foam should act as vapor barrier, right?

Do I need to patch it somehow (low expanding spray foam?) before installing framing? Any value in replacing all the old foam with newer product?

white Styrofoam insulation with gouges and glued on drywall

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    I would leave the foam in place it will be better at resisting moisture. I have seen folks put r30 in basement walls the being it would help but since the below grade walls are at a relatively constant temp the additional insulation really did not help. If you wet the pieces that are stuck the Sheetrock will crumble just leaving the paper – Ed Beal Sep 13 at 14:24
  • thanks for the tip for crumbling the Sheetrock! – jpx Sep 13 at 22:38
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With tears like this, it does not appear to me that this can effectively function as a vapor barrier. I would remove and replace with modern, more dense foam. If your wall is below grade, I would not add 2x4 walls/insulation especially if the only reason for doing so is adding insulation. If you are doing it to add electrical or plumbing, I still would not waste money on rock wool, unless the wall is above grade.

  • wall is 1/2 above grade and climate gets pretty cold (Ottawa Canada, and I think 99% design temp is around -13F) I think code is now R20 on basement walls and R24 on above grade walls – jpx Sep 13 at 22:25
  • I was thinking of filling the tears with low expanding spray foam and taping all the seams? – jpx Sep 13 at 22:27

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