I’m preparing to install a hardwood floor on a slab on grade. I was planning to put down moisture barrier,sleepers, T&G plywood. Do I rip 1 1/2 styrofoam for in between? Should I be worried about using solid 5/8 hardwood flooring? The slab actually sits on 6″ gravel, poured walls and slab in one pour and the finished floor sits 4-8″ above grade.
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Hopefully, the slab is insulated underneath, that's where the foam should be.
The foam in between the sleepers isn't a bad idea, though I have heard about this method leading to squeaks. If you are using 2x for sleepers, you might want to just use 1" foam to keep the underside of the subfloor from possibly rubbing against the foam.
what do you have for a vapor barrier under the slab ?
if you're confident you can control the moisture level, you can do a direct glue-down on the slab