Determining How Much OSB to Purchase
Calculate the square footage of the roof. OSB comes in 4-by-8 foot sheets, totaling 32 square feet each. Calculate the number of sheets needed for the roof project, allowing several extra for waste and cuts.
Determining the Thickness
OSB comes in various thicknesses. The thickness of the OSB used for a roofing project is determined by the spacing of the rafters. The OSB council recommends OSB sheeting between 5/16 inch and 7/16 inch for rafters that are placed 16 inches on center or less. OSB of 3/8 inch to 1/2 inch is recommended for rafters spaced 24 inches on center. OSB sheets 3/4 inch or thicker is suggested for rafters space up to 48 inches. Heavier OSB and longer nails should be used in areas prone to hurricanes or other high-wind weather patterns, regardless of the rafter spacing.
When applied to a roof, the OSB sheets should be placed about one eighth of an inch apart to allow for expansion. According to the website of the Structural Board Association, the minimum spacing of the nails should be every 6 inches along the edges of the board and 12 inches on center in the middle portions of each OSB sheet. Standard 8 penny nails are used for fastening OSB to rafters in roofing applications. Longer nails should be used for heavier OSB is used.
Labels are printed on the OSB denoting the thickness and grade of the product. Many products also include a label denoting which side of the board should be placed facing up on the roof.
Finishing the Project
Moisture barrier and shingles should be applied to the roof as soon as possible. That prevents damage to the OSB from weather.
Installers of OSB should use caution during roof applications. OSB can be slippery when wet. Installers should use soft-rubber-soled shoes or boots and all proper safety equipment. Some brands of OSB apply texture to one side of the sheets to provide better traction.