i am renovating a basement and want to know the best way to insulate the floor? I'm thinking about laying pressure treated 2x4's flat on the floor and laying 1" styrofoam insualtion sheets in between them and covering with 3/4" tongue and grove plywood - do i need plastic? any other suggestions?

Look around for a new type of plastic sheeting on the market. It is dimpled which creates an air gap for insulation and damp proofing. Plywood is then nailed over top of it into the concrete floor. This has the big advantage of saving valuable head room in the basement. Don't know anything more other than I have seen it in place and the floor was warm and solid.

I put tight-loop berber over an 8-pound pad in my basement and its been fine. The key is the 8-pound pad.

As for palstic - only needed if you have a miosture problem. Tape a 3'x3' plastic to the floor. Leave it for a few days. If there is moisture between the floor and plastic, then you have a moisture problem. Otherwise, plastic isn't needed.

pgaszek

The way you've described should work ok. Put the poly vb down. Once you've insulated the floor, you've effectively isolated the underlaying concrete from to heat, thereby making it cooler and increasing the likelyhood of condensation (Putting carpeting directly over concrete can have a similar effect, especially in areas with a colder ground temperature). The poly will 1/help to minimize moister getting to the concrete and 2/ keep any moisture from effecting your floor.

I wood suggest using treated 2 X 4's and you may just as well use 1 1/2 foam, glueing everything down to eliminate squeeks (filling the space also helps to eliminate air which carries the vapor to the concrete).