Question: can durock be used as subfloor?
Answer: Subfloor should be minimum 5/8" APA span-rated plywood or OSB with an Exposure 1 classification or better. Minimum 3/4" APA span- rated plywood or OSB with an Exposure 1 classification or better. Cover base with USG Durock™ Brand Tile Membrane, 15 lb. felt or 4-mil polyethylene and attach with 1/4" galvanized staples.