I am remodeling a recently purchased home. The previous owners converted the back porch into a bathroom. (good idea) They fed the plumbing through the floor joists, put some foam insulation below the joists (most of which is falling off) then they added electric baseboard heating, cut some vents in the floor and crossed their fingers (bad idea). Currently I have the floor, subfloor and all walls removed. What do I do now? I could try more foam boards under the joists, (there is about 3-4 feet of open air before the ground former porch remember), force air in between a joist and vent up through the floor? This would be ok for the water pipes in that joist but what about when they cross over to other joists that don't have air forced through them?

I've run into interior renovation situations were I really wish I could provide a thermal break from stud to drywall. In areas like bathrooms with exterior walls it would be really nice to keep the drywall insulated from the stud. Even on a perfectly done job I'll see the shower steam condense on the screw heads and around framing first, because those spots are always the coldest. I know the framing is best insulated with rigid foam on the outside of the house but I'm always working with older homes which do not have foam over the exterior sheathing. Yes, I could put xps over the entire interior framed wall, then drywall, but I'd never mount something like a shower surround over top of foam. Foamular/xps is too squishy and would compress between the shower surround and the framing. You could do xps then plywood, then finish the room, but now you've added a lot of thickness and that'll cause issues. I'm wondering if there is a non-compressible material that can act as an interior thermal break from the framing. Maybe just a quarter inch thick. I don't need it to hold nails or screws as I'd plan my framing behind it. Thanks!