I'm sure that this question has been answered a million times already.

I built a 280 square foot home addition on concrete slab over 35 years ago. Over the slab, we laid down plastic, installed 2 by 4 sleepers with foam insulation batts between on top of the plastic, installed 3/4" particle board on top of the sleepers and then and then topped it off with carpet over padding. Now we want to replace the carpet with nailed solid hardwood flooring (don't want to use any glues). I realize that I have to eliminate/replace the particle board. I have also read that you can nail the floor directly to the sleepers, but to avoid height issues with regards to baseboards and doors, I plan on replacing the particle board with 5/8" or 3/4" plywood. I could even put another layer of plastic sheeting between the sleepers and the plywood.

I had a contractor stop by to discuss my job and he discouraged using solid hardwood flooring for the new floor to avoid "problems" down the road. Yet, I have visited several web sites that support installing solid hardwood flooring over concrete and describe several techniques for doing so. The nay saying contractor planted the seed of doubt in my mind. I'm just reaching out to this forum to see if many other folks would discourage using solid hardwood flooring for this application.

PS: Engineered flooring is still under our consideration (bamboo, laminated and all others are out) and selecting a floating engineered flooring option would save me a lot of cost and time replacing the particle board "sub-floor". I'm really just trying to determine if solid hardwood flooring is a viable option for this application so that if we want to, we can go that way without reservation. Thanx...

Nailing directly to the sleepers or joists had been the norm out here for centuries until they started with 6" solid wood plank subfloors and ply underlayments. Tons of them out here in the old neighborhoods with floors 80, 90, 100 years old.
I'd want the joists to be 12' apart.