Framing Floor Over Garage Slab – GreenBuildingAdvisor

I’m converting a garage into living space for a client and he wants to raise and insulate the floor, so I’m planning on using 2x6s and insulating joist bays. My thought is to put down a vapor retarder over the concrete and tape it to prevent moisture from coming in through the slab, and this would allow me to use KD for joists. I’d rather not use PT because it warps as it dries and it seems unsafe to use indoors, but I wonder if the building department will want joists to be PT even if it’s not in direct contact with concrete. The floor is pitched because it’s a garage, so the lumber won’t even be touching slab except where slab is highest. Unfortunately, this town’s building department is very unresponsive to questions, unless I physically go there and talk to inspector. If KD is fine here, what would you recommend as a vapor retarder, 6 mm poly?