Hi all- I had a couple questions on our partial basement remodel. We’re in climate zone 5, Rochester NY. We have a 1970s ranch home with a concrete block basement. My plan for the exterior wall assembly is 2 inch rigid foam fixed to the exterior block walls using adhesive, taping the seams, 2×4 framing with roxul or fiberglass batt covered with ½ drywall.

I have some questions before we get started.

First: we are only finishing half of the basement. I’d like to know the best practice for the wall assembly that divides the unfinished space to the finished space. Can I just build a 2×4 wall, ½ drywall on each side with batt insulation in between, no poly?

Second: Its common in my area for basements with our without sump pumps to have a ‘floating slab’- that is a 1.5-2 inch gap/crevice between the exterior block wall and the concrete slab along the perimeter of the basement. There is also drainage tile along the perimeter that connects to the storm drain. Can I bring rigid foam to the slab floor knowing there is a void? Do I need to address in anyway the void?  

Third – my rim joists are insulated with 2inch rigid foam and roxul. In front of the bottom sill plate you can see the open cavities of the block wall. Should these cavities be filled/sealed and otherwise connected to the rigid foam that will line against the wall?