What subfloor should HardieBacker board be installed over?
The minimum subfloor specified is 5/8″ exterior grade plywood or 23/32” exterior grade OSB subflooring. HardieBacker board must be installed in accordance with local building codes and the floor must be engineered not to exceed the L/360 deflection criteria, including live and dead design loads, for the specific joist spacing used. HardieBacker board is not designed for use over concrete.