Wood-Based Structural-Use Panels are well known for their use in sheathing for roofs, floors and walls. Plywood and oriented strand board (OSB) are two types of wood structural panels commonly used in residential and low-rise commercial construction. For a given span rating, OSB is as strong as 5-ply plywood. When used in typical sheathing applications, OSB and plywood may be used interchangeably. Particleboard is another type of wood panel that is seldom used in structural applications. It is, however, often used as underlayment over floor sheathing, in cabinets and furniture.
Bond classifications for wood structural panels provide a measure of the moisture resistance of the glue bond under intended end-use conditions. Plywood with an “Exterior” bond classification is suitable for repeated wetting and redrying or long-term exposure to weather. Plywood and OSB with an “Exposure 1” bond classification are suitable for use when not permanently exposed to the weather.
Plywood is made with plies (sheets) of wood veneers that are glued together under heat and pressure. It replaced shiplap boards as sheathing on walls and floors and spaced boards on roofs. Plywood is stronger and stiffer when the grain of the face veneers are oriented perpendicular to supports, which is the typical orientation for most floor and roof applications.
Oriented Strand Board
OSB was invented in the late 1970s in response to greater demand for housing and commercial buildings, a decreasing supply of older trees, and increasing environmental restrictions on logging.
OSB is made with layers of thin, rectangular strands or flakes of wood that are produced by feeding freshly cut hardwood or softwood logs through a cutting machine called a strander. Each layer of strands is alternately placed perpendicular to the previous layer, which provides bending support in two directions.
Applications in Construction
Wood-based structural-use panels are available in many thicknesses, ranging from 1/4″ – 1-1/4″. They are manufactured as one of several types, identified by the intended end-use. These panels are used for sheathing on roofs, subfloors and walls; underlayment in floors; single-floors (combination subfloor and underlayment); tongue and groove; siding; and structural insulated panels.