Deciding on what is the best product for your roof decking can be confusing. Should you use the old school proven plywood or the Oriented Strand Board (OSB).
Building codes, the Engineered Wood Association, architects and most builders rate plywood and oriented strand board (OSB) equal in strength and durability. Like-thicknesses of these two products can span the same distances between studs or rafters, weigh about the same and offer similar nail-holding abilities.
OSB has its advantages. Having a painted sealed edge protects against swelling due to water entering the edges. Some panels have a rough surface making them easier and safer to walk on. OSB panels have lines at 16- and 24-in. intervals so you know where underlying studs, rafters and joists are for nailing. In our areas 1/2-in. OSB costs a few dollars less per sheet than 1/2-in. plywood. And OSB is available in larger sheets.
OSB has swell if exposed to water for a long period of time. Plywood will de-laminate if exposed to water for longer periods. Care should always betaken to store both on the job site covered and under-layment should be installed as quickly as possible. Neither should be stored out side in the rain.