Our unfinished basement has a concrete floor and poured concrete walls. It has stayed completely dry all year for a decade since the house was built. I will be framing the exterior walls 1" from the concrete with 2" of closed-cell spray foam as insulation and moisture barrier. I plan to insulate the floor with 1" polystyrene foam-board glued to the cement, then 3/4" pressure treated sleepers screwed to the foam, then 3/4" subfloor screwed to the sleepers, then hardwood or laminate flooring on top of that.
Must the interior walls be framed first and nailed directly to the concrete floor, with the foam and subfloor built around them? Or can the foam, sleepers, and subfloor be put down first with the interior walls sitting on top of them? The latter would obviously be far easier as the foam, subfloor, and sleepers would not need to be cut around a very large number of walls in a small space. The difference could be a five day job becoming a five week job (I don't have a lot of free time to dedicate to this project each week).
I understand that nailing through the subfloor would not provide the same stability as nailing directly to concrete, but these are non load-bearing walls that will likely support little-to-no weight. Are there any other disadvantages, or things I need to look out for or address?
Best Answer
I think you can do both, but framing walls on top of subfloor is potentially less work.
If you use a product like DriCore for the subfloor, they even explicitly recommend you frame on top of their subfloor product. They do, however, recommend you screw the framing through the subfloor into the concrete with something like 3" Tapcons spaced every 4 ft through the bottom sill of the framing.