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Rigid Foam board insulation on basement concrete wall OVER a french drain dimple board section

AF2022 | Posted in GBA Pro Help on

Hello GBA – from my research on this forum, seems Martin H. may be the guy to answer :-)…  My contractor is asking I make a decision fast!
So we are doing the popular XPS rigid foam board over my basement concrete block wall to serve as my Moisture barrier… however I have about 4-5 inches of the plastic waffle/dimple board peaking up from my french drain system thereby not allowing a straight laying down of the rigid foam board onto the wall to go all the way down to the floor like truly intended… 

Is it ok to just lay the foam board right on top of where the waffle/dimple board and not go all the way to the floor?  Else that would require complex “notching” and cutting etc. and might be overkill.. mixed opinions out there 🙂  
PIC ATTACHED.  *I think it should be OK as long as we seal w/ Spray foam?  where the rigid foam board meets the top of the lip of this waffle/dimple board piece for air seal
Thank you

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  1. Thompsonfam31 | | #1

    Hi.. did you find a solution to this problem yet? I’m in same scenario and trying to figure out how to approach.

  2. Patrick_OSullivan | | #2

    My foam lands on the top edge of the dimple mat. The foam to dimple mat junction is sealed with flashing tape (3m 8067 in my case). The dimple mat is covered by foam as well, just not as thick as the rest of the wall. If this is unfinished space, I wouldn't be as concerned as foam over the dimple mat. It's going to be the warmest part of the wall, and is a relatively small area, so the heat loss is minimal. But, the face of the dimple mat could still be below the dew point and could therefore become a condensing surface.

    Photos attached show my install, including before and after the thinner foam is glued in to cover the dimple mat.

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