Short version: If I install 3" of rigid foam over a poured concrete foundation wall that has been sealed with Xypex, will I have any moisture issues if I install plywood directly over the rigid?
Longer version: I'm finishing a basement space as an eventual bedroom. To be code-compliant, I'll need to bring the walls up to R-15 (and address egress as well, but that's another subject). My basement walls are comprised of 4 feet of poured concrete with 3.5 feet of framing on top. I'd like to save as much square footage as possible, and therefore not build a 2x4 interior wall after installing rigid.
The plan I've devised is to tackle the upper, framed portion of the wall and the lower, poured concrete portion of the wall separately (see image).
- Upper, framed portion: air seal the stud bays (exterior sheathing is butted board), stuff bays with rock wool, and install 1/2" drywall.
- Lower, concrete portion: seal concrete with Xypex, install 3" rigid foam (polyiso?) with adhesive, install 3/4" plywood
Electrical will be installed with surface-mounted conduit to the plywood.
No foundation sealer is perfect, but will my wall still breathe enough that I won't experience any moisture issues?
My contingency plan would be to add 1" furring strips to the rigid, then install the plywood over that.