I am a remodeling contractor ... done lots of stuff, and done it well ... but this will be my first time installing a wood floor.

The customers house was built on a concrete slab with a screened porch as an integral part of the main house. The main roof continues over the porch, which is raised about 12-14 inches above grade. No apparent moisture problems. Now he wants to replace the screening with windows and turn it into air conditioned space, and add a wood floor at the same time. There is adequate money to do the job right ... don't need to cut corners, but we're not going to waste it either.

The porch slab is dropped about 5 inches from the house floor, and he wants them to be essentially flush. Wood has not been selected, but will probably be 3/4" prefinished strips. My current idea is to build a subfloor frame of 2x4s on edge (like a stud wall laying on the floor), then a layer of 3/4 ply, then the floor. Total arera is about 450 sf, a rectangle with a wide area in the middle.

Questions: What should I put on the slab under the 2x4s? How would you fasten 2x4s on edge to the slab? Is 3/4 ply enough, or shoud I use two layers of 5/8 (I can rip the studs thinner if necessary). Is there any advantage or disadvantge to filling the stud bays with fiberglass batts?

I would use pressure treated 2x4's over concrete and install a 6 to 8 mil polyethylene vapor barrier over the slab, then your 2x4 floor joists. For more stability, consider using 4x4's instead. As far as attaching them to the slab, use a Simpson Strongtie connector http://www.strongtie.com/products/conne ... ml#gallery
3/4" plywood is great for floors. Be sure your joists are 16" oc. And yes, installing fiberglass in the bays between the joists would be a good idea. There are also foam board insulation products as well. After your 3/4" plywood subfloor, lay 15 lb. asphalt felt paper over the plywood and under your finished wood floors. There you have it!