Energy efficiency rebates in Iowa.

Mixed foundation materials (Clay and Concrete blocks): how insulate for remodel?

A homeowner in Des Moines is renovating the basement of a 1924 brick house after finding mold behind old insulation that had been pressed directly against the foundation wall. The foundation itself is a mix of materials: clay brick on part of the wall and concrete block on the rest, joined by an uneven seam, likely from a past repair when a sump pump and drainage trench were added. A foundation company is now shoring up the walls and plans to add a vapor barrier sheet, but the remodeling contractor wants to frame over that with plain fiberglass insulation that has no backing. The homeowner is worried this setup will let warm indoor air pass through the fiberglass, hit the cool vapor barrier, and condense into moisture that soaks the insulation and grows mold again, just like before. The core problem is that the two foundation materials may need different insulation approaches, and the homeowner isn't sure how to bridge them, especially at the seam and at the drainage trench, or whether foam board can be used on the concrete section while something more breathable handles the clay brick. The contractor's team has said they can't use rigid mineral wool insulation without exterior waterproofing, and has otherwise deferred to unnamed "partners" for technical decisions. This is a homeowner's request for advice on a real, tricky renovation problem, not a policy or program announcement. There is no rebate, deadline, or general upgrade news here for other homeowners to act on. If you're facing similar mixed-material foundation walls in an older home, this thread is a reminder to think carefully about how vapor barriers and insulation types interact before finishing a basement.