Metal sheathing w/minimum thickness of 24 gauge (0.024 in. [.61 mm]). Trapezoidal spacing of 8 in. (203 mm] to 20 in. (508 mm) in one-inch increments. Plywood w/minimum thickness of 5/8-in. (15.9 mm) CDX. Concrete decking w/minimum thickness of 6.5 in. (165 mm) & minimum concrete compressive strength of 3000 PSI (20.7 MPa).