Leave or replace existing basement insulation – GreenBuildingAdvisor

Rip it out, batts against the foundation with interior side poly will probably be moldy. Ideally, you want ALL the R value in the form of a nonpermeable insulating material (some kind of rigid foam) in a basement, but you can use foam right over the wall and then batts inside of that. You don’t want to use interior side poly regardless here.

You’ll want to insulate the rim joist area at the same time. There are various ways to do that depending on how that area is built. Common ways to go are to spray foam the entire thing, or

“foam in” blocks of rigid foam (which is what I usually do, using blocks of EPS).

Bill