I have a living area on a concrete slab over a garage below. Conditioned space over unconditioned. The floor also needs to be fire rated 1 hour so I will be using spray applied fire proofing over the concrete slab and beams. I need to achieve a decent r factor on the floor. What products are available?
Usually the concrete slab will be sufficient to achieve the 1-hour rating; why wouldn’t it be in this case?
Although it sounds expensive, I would almost suggest a layer of rigid plastic insulation over the concrete slab with a layer of fire-rated cement board over the insulation to be used as a subfloor surface. Two inches should get you close to R-12. You can put this underneath, but you should really should not leave it exposed.
Look at K-13 insulation by International Cellulose http://www.internationalcellulose.com/products/k13.html