There is grey foamboard between house foundation & garage floor slab. I'm not sure how far down it goes, but it starts at bottom edge of drywall. Is this insulation? Or part of an expansion/isolation joint filler system?
Some looks either corroded, weather damaged or chewed on. Underneath my fireplace bumpout there IS a chewed hole from rodents (question about that later)!

I'm having concrete replaced & need to know how to deal with this foam:
Should contractor replace it during the pour?
Should it be removed & the space between house & new slab narrowed with nothing in between?
If it's needed insulation (I live in WI) & MY responsibility, how/when do I remove & replace - before or after new concrete?

4 inches grey foamboard between drywall and concrete floor

grey foamboard

1 Answer 1


In the picture it doesn't look like foam board, it looks like a concrete wall. Aside from that, knowing about "perimeter insulation", it is designed to keep the cold from going into the slab, so it does not radiate into the room, or in this case the garage. It, depending on the building code for your area and the time it was built, the insulation could go down along side the foundation wall until it goes to the frost line, which is the depth the ground freezes during cold weather. Either that or it could go only as deep as the concrete thickness is, then connect to a layer just under the concrete so the foam keeps the wall from radiating, and the foam under the slab, most times 2' in, keeps the slab from getting to cold.

The first way I describe, the concrete guy may not damage the wall enough to warant replacing. If it does get damaged, it could be cut anlong a straight line, and just replace what is damaged. If it is the other way, they will definatly need to replace the insulation, there will be no way to keep from destroying the insulation that is directly under the slab.

If these guys are legit, they will already know this.

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