Keep and patch, or replace white rigid foam during basement remodel?

Question

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?

peinal · Answer

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.

Answered by peinal on October 12, 2020

Keep and patch, or replace white rigid foam during basement remodel?

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