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Discussion Starter · #1 ·
First post, checked here and Jon Eakes site but can't find an answer.
Renovating a 70's basement in Montreal, Quebec with 4ft below grade and 4ft above grade wall in concrete. Currently has 1inch white foam board (no name on board) which seems to be the bead board not recommended for basements - it is also damaged in a couple of places (see picture 1).

Question - can I put 1inch Dow blue board XPS (Cladmate) directly over it (mechanically attached with foam glue, tapcon and foamboard washers) or should I just remove the existing foamboard and replace with 1inch XPS?
Afraid it might take the cement wall surface with it, as it is well attached except at the very top (pic 2). It also is warm to the touch, so seems to be doing its job (minus 15 C here).

Will be tuck taped for seams (including white foam board seams which are currently not taped), low expansion foam for the perimeter.
Also not sure what to do at the corner where the exterior meets the interior (party) wall (pic 3) - has a 6inch uninsulated back turn with a ledge - was thinking of putting 2inch Dow Blue Wallmate there.

Interior wall will be 2x4 BluWood with foam sill gasket directly against the foamboard with Roxul, no vapor barrier, then .5inch mildew resistant painted concrete denseboard.

Thanks in advance for any replies.


Retired Moderator
25,770 Posts
Someone will answer you--Home Sealed--windows on wash--and GBR usually have answers that are easy to understand and are well researched---

I say--go for it---But I,m not an expert on insulation----that would be a time consuming mess to remove--it is still sound---I'd bury it under another layer ,like you are thinking.
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