Insulation, Radiant and Vapor Barriers - insulate below subfloor of unfinished bonus room

I am finishing a room over an unheated garage. The garage ceiling is sheetrock but I do not know if it is 1/2" or 5/8". I need to insulate below the subfloor (above the sheetrock). Should I blow in cellulose, and if I do will the sheetrock hold the weight if it's only 1/2 "? Or do I use batts of fiberglass and push them under the subfloor? Do I need a vapor barrier below the subfloor?

Thanks

You ought to have a vapor barrier, but it would have to go over the insulation toward the living space. 1/2 inch will hold cellulose, but may sag. 5/8" is recommended for ceilings. You could blow the insulation into the voids.

Pushing the batts under the subfloor sounds like a good idea. It might help to have a string or something to pull on the other end of the batt. Kraft face toward the living space. The plastic wrapped insulation might be easier to push under the subfloor.

Hope this helps.