There are typically two types of sheathing used on modern-day roofs: plywood and oriented strand board (OSB).  Plywood is comprised of layers of veneer, or sheets of wood, laminated at ninety degrees from one another to create strength by crossing the grains of the wood.  Oriented Strand Board is made from shavings of wood mixed with adhesive and placed under very high pressure to form the sheet.  Veneer used in plywood is often riddled with imperfections requiring “patches” or fillers to create a more unified surface.  The problem is there is no guarantee that the inner layers are free of voids.  The method of creating OSB eliminates any voids within the sheet and is denser due to the high pressures.  Economy Garages prefers to build with OSB due to the consistency of the product.