I'd like to revisit an upcoming project ... installing 500 sf of wood floor over a concrete slab. In this case I have the luxury of no height restriuctions ... in fact that is part of the project. It's an enclosed porch that is about 5 inches dropped from the house floor, and they want it flush.
The question at hand is how to fasten the floor joists to the slab. Attached is an idea. Start with 2x4's laid flat, with a bead of PL, and Ramset every 36" to the slab. Then 2x4's standing up at right angles, toe nailed to the runners. These 2x4's would be tapered as needed to make the final floor flat and level. Rigid foem between the joists. 3/4" cdx ply glued and screwed to the joists. A layer of 15# felt over the ply. Wood flooring nailed to the ply.
My only concern is the 2x4 joists spanning 24 inches. Is that too much? Actually the span will be about 21 inches.
All I know, I learned from Luka.
I'm sorry, I thought you wanted it done the right way.