Hi all,

Newbie here, hoping to gain a little knowledge. I'm converting a portion of my barn to habitable space and am planning to put down hardwood floors. I'm a carpenter, but don't specialize in flooring and have only done a handful of jobs, all of which were over wood framed subfloors. I'll outline my plan from the ground up....

1. EXISTING - Slab on grade, poured in July, over vapor barrier. This part is done already. I intend to either seal it from above and/or put down 6mil poly vapor barrier as well. It seems like poly is most common, any great benefit to the paint on sealer, or both?

2. INSULATION - Continuous layer of 4" Rigid polyiso foam board. (I was able to get a load of this from a salvage yard, otherwise would have chosen a thinner product) I am not sure of moisture issues with polyiso, I know it isn't closed cell like XPS, but in my case does it matter? I can potentially find another use for the 4" and go with a 2" product as well.....

3. SUBFLOOR - I'm hoping to float a 3/4" T&G plywood subfloor over the foam, no attachment to the concrete....I thought about maybe tacking down furring strips to it to keep it from sliding until I installed the hardwood. Put a layer of 15# felt on top of this. Alternatively, I considered laying sleepers on top of the foam, then nailing hardwood directly to them, or possibly putting plywood on top of sleepers....but it seemed a little unnecessary...it seemed like it would be stronger to go with plywood subfloor, but would sleepers on 16" centers work fine too?

4. FINISH FLOOR - Probably red oak, 3/4" thick, solid wood, nailed or stapled down.

My main hangup is figuring out if floating the plywood or sleepers over the foam is going to be a problem in getting a good level subfloor. The slab is in good shape and pretty darn flat.

Any other thoughts or considerations from the experts would be welcome!
Thanks!