Oriented strand board (OSB) is similar to plywood, but instead of thin strips or plies layered at a 90-degree angle, OSB is made of interlocking strands of 3- to 4-inch wood lengths that overlap and interlock at a 90-degree angle. Used for subfloors and single-layer floors, OSB is typically sold in 4-by-8 foot panels. Its ability to bear weight is comparable to plywood.
The Structural Board Association (SBA) reports that 7/16- and 19/32-inch-thick OSB panels applied on 16-inch joists on center (OC) can bear 100 pounds per square inch (psi) live weight and 10 psi dead weight. OC is the distance from the center of one joist to the center of the next. Live weight is that of people or animals. Dead weight is that of heavy, motionless mass. Panels that are 19/32- and 5/8-inch-thick, set on joists 20 inches OC, can support 100 psi live weight and 10 psi dead weight. The OC distances in these load-bearing calculations are the maximum for these panel thicknesses. More joists mean stronger floors that are able to bear more weight.
Panels of OSB that are 23/32- and 3/4-inch-thick, set on joists 24 inches OC, can bear 100 psi live weight and 10 psi dead weight. Panels that are 7/8-inch and 1-inch-thick, mounted on joists 32 inches OC, can bear 100 psi live weight and 10 psi dead weight.
OSB that is 1-1/2 inches in thickness, set on joists 48 inches OC, can bear 55 psi live weight and 10 psi dead weight.
For added strength, apply thicker OSB on joist spacing recommended for thinner panels. For increased floor performance or engineered flooring, the SBA recommends combining I-joists with OSB flooring that exceeds span ratings. I-joists are manufactured composite joists.