I am repairing an old garage / small barn (24′ x 26′). Downstairs, the owners park their cars on a dirt floor. Upstairs is being converted into a painting studio. The floor was originally 2 courses of rough, random width 1x run perpendicular to the joists. I am going to install 3/4″ A-C Ply as the new finish floor. The 4″ x 8″ joists range from 24″ to 30″ o.c.. I’ve stripped off the top layer of flooring to facilitate leveling the floor, and to remove much of the crap that worked itself in between the two layers.
I’m going to use spray polyurethane foam to insulate the building, but wanting to leave the underside of floor exposed, was thinking of laying 2″ rigid foam on top of the first layer of floor. At first, I thought putting a course of 3/4″ plywood right on top of the rigid foam would work but after talking to DOW about their Tuff-R panels, was told that they weren’t designed to support a floor. And to use sleepers instead.
So, my question is, can I use 2 x 4 sleepers run perpendicular to the joists to support the plywood floor? The sleepers (or strapping, more accurately?) The 2 x 4’s would be on the flat, dropping my rigid insulation down to 1 1/2″, and run 16″ o.c.. Between the widest spaced joists, the 2 x’s would be spanning 28″. Too much? Can/should I strip off the remaining layer of 1x flooring and install the 2×4’s and foam board directly to the joists?