Oriented Strand Board (OSB): Review uses and specs for these engineered-wood panelsOriented strand board is a structural panel material used for subflooring, roof and wall sheathing. But not all OSB panels are created equal. Choose the OSB product with appropriate moisture resistance and milling features for your application and local weather conditions.

    Oriented strand board, universally known as OSB, is an engineered-wood structural panel that has replaced plywood in many homebuilding applications, including subfloors, and roof and wall sheathing. Unlike plywood, which comprises laminated layers--or plies--of wood veneer, OSB is made of thin compressed-wood strips of varying sizes. In manufacturing of OSB, mats of wood strips with their grain oriented in a single direction are created first, then three or more mats with the grain of successive layers running perpendicular to one another are bonded together with heat and phenolic resin under high pressure. (To make a 5/8-in.-thick panel, manufacturers start with a 5-inch-thick mat of wood strips.) The result of this multi-layered bonding is a panel that's dimensionally stable, extremely stiff, and remarkably smooth. OSB has no voids, knots or checks (splits), and it's moisture resistant. And if all that weren't enough, OSB also offers excellent fastener retention, meaning that nails hold fast. Major manufacturers of OSB include Georgia Pacific, Martco, Louisiana Pacific and Kronotex.

    OSB: Panel Sizes and Thicknesses
    The standard OSB panel is 4 feet wide by 8 feet long. Panels measuring 4 by 9 feet and 4 by 10 feet are also readily available, and through special order, some manufacturers (including GP) offer 4-foot-wide panels in 12- and 16-foot lengths.

    OSB is available thicknesses ranging from 1/4- to 1-1/8-inches thick. It's commonly available in both square-edged and tongue-and-groove edged panels. Some T-and-G OSB panels (such as LP's Top Notch brand) have notches cut in the tongues that allow water to drain through, thus eliminating problems associated with standing puddles of rainwater that often collect before a house is enclosed.

    OSB: Basic Applications
    OSB is used primarily for subfloor applications, and also for wall and roof sheathing. It can be fastened with nails or screws, and most panels come with pre-marked lines that show where to place fasteners. Every OSB manufacturer recommends leaving a 1/8-inch expansion space between panels; oriented-strand board panels should not be butted tightly together.

    For subfloors, OSB can be doubled-up using two thinner layers, or a single, thick layer can be installed. Padding and carpeting can be laid directly over an OSB subfloor.

    For wall and roof sheathing applications, panels ranging from 3/8- to 3/4-inch thick are most common, depending on the building's specific requirements. On maximum span ratings on roofs, install metal clips onto the panel edges to prevent deflection.

    Here are some typical span ratings for OSB:
    •19/32-inch-thick panel spans joists/studs spaced 20 inches on-center
    •23/32-inch-thick panel spans joists/studs spaced 24 inches on-center

    It's also important to note that many manufacturers have a line of several oriented-strand board products that look basically the same but have varying degrees of moisture protection. For example, standard OSB (PS-2 grade) is considered “moisture resistant,” and is suitable for most applications. However, when building in wetter regions that receive more than an occasional rain shower, choose an OSB product that's designated as “weather and rain resistant.” For the best protection against moisture, choose a premium OSB that's rated for “wet environments.” This panel will survive in the very wettest weather without edge swelling or deterioration.

    Additional Resources
    APA - The Engineered Wood Association
    Canadian Wood Council
    OSB Guide