I have seen this discussion here before but cannot find anything now. A client has gotten conflicting advice from 2 professionals on this. I suggested he contact a third. He said that was why I was there. So I guess I had better come up with an answer. This is a house with poured concrete walls in SE Wisconsin. Finished basement has 2X4 drywall and stud walls with batt insulation and no vapor barrier. Due to flood damage, the client had to cut open the walls and wants to know if he should take them down and put in a vapor barrier, and where would it go.

I am thinking basement walls do not necessarily act like those above ground. However, I assume even with temp swings from -20 to 90, the exterior of the foundation is likely to always be colder, so a vapor barrier just under the drywall might make sense. However that would put insulation unprotected against the concrete, unless one created an air space. At the same time, it seems to have done just fine for 6 years without any vapor barrier.

A factor in this may be that the exterior of the foundation is also insulated. This is a second question. What is this stuff? Anyone know a brand name? (see photo). It is a white foam board material with a covering that seems to be permanently bonded to it. It looks like a burlap material or maybe woven plastic that has paint or some other liquid applied to it. I assume the material is to protect the foamboard from UV rays. But it seems to shrink at the joints and expose the foam. What would be a reasonable repair?