Installing a basement subfloor
a friend has asked me to help install a basement subfloor.
house was built in 1950 and has a concrete slab floor in the garage/basement. There is a room built in the back of the garage (came with house originally). Floor is currently concrete slab with glued on 12"x12" vinyl tiles. The location is northern CA where the weather is moderate but it does get cold some nights (but not cold like east coast cold). The room has no built in heat & they use a space heater right now.
My plan is to put a 6 mil poly sheet on the floor, then 2" rigid foam tapes at seams, the furring strips/sleepers, then 2 layers of 1/2" plywood (each layer offset from other).
What I want to know is can I leave the 12"x12" vinyl in place or do we really have to try and scrape that off? We can put poly sheet right over the vinyl tile. Or we could paint an epoxy paint over the vinyl tile and then add the poly sheet and then do the rest.
There is a moisture problem in that room. The owner put a carpet over the old 12"x12" vinyl tiles to make it look/feel nicer, but the carpet feels slightly dank and room smells dank when you first open the door and enter the room.
Also - separate question - The walls are covered with drywall now, but the lower part of the walls (about 16") is the concrete footing which sticks out into the room. It has an angle to it because it flares out quite a bit at the bottom and the top is about 4" wide. Any suggestions on how to box that concrete so they can have a nice lower shelf that is basically rectangular shaped instead of trapezoidal?