Oriented strand board, or OSB, is a type of lumber that shares many properties with plywood or fiberboard. While other types of wood sheeting typically feature a smooth surface, this type features a rough surface made up of hundreds of wood chips. While these scraps of wood may appear randomly placed, each piece of wood is actually aligned to maximize the strength of the panel. Manufacturers combine multiple layers of these wood chips to create a board up to 1 inch (2.54 cm) thick. The layers are then subjected to high levels of heat and pressure and joined together with resin to create a secure bond.
Builders use oriented strand board to construct wood-framed homes and commercial buildings. These boards serve as sheathing to support lumber framed walls and roofs, and also serve as a base for interior or exterior finishes. For example, builders may fasten siding or roof tiles to the boards, or even apply stucco or plaster over the surface of the OSB. When installed over top of floor joists, this type of material can also serve as a support base for flooring.
OSB comes in a number of varieties to suit the needs of different applications. For interior applications, installers rely on interior grade products, which are designed for areas with little to no moisture exposure. Exterior grade oriented strand board can be used in areas subject to minimal amounts of moisture or humidity changes, while moisture-resistant products must be used in wet areas.
One of the primary advantages of using this material is its low cost compared to plywood or fiberboard. While most experts agree that plywood and oriented strand board share virtually the same properties in terms of strength and durability, OSB is less expensive, which can reduce overall building costs. Oriented strand board also offers a more uniform and consistent construction, resulting in greater stability. Because it consists primarily of wood scraps, OSB is also considered more eco-friendly than plywood.
Excess moisture can lead to big problems with OSB, particularly if the boards are not sealed properly. While OSB generally gets sealed during production, field cutting results in unsealed edges that allow moisture to seep in. Once it gets wet, OSB tends to swell or warp, resulting in poor performance. Wet oriented strand board may even telegraph through floor or wall finishes. To prevent these types of problems, installers must reseal any edges cut during construction to minimize the risk of moisture exposure.