Oriented strand board (OSB), also known as flakeboard, sterling board and aspenite in British English, is a type of engineered lumber similar to particle board,
formed by adding adhesives and then compressing layers of wood strands (flakes) in specific orientations. It was invented by Armin Elmendorf in California in 1963. OSB may have a rough and variegated surface with the individual strips of around 2.5 cm × 15 cm (1.0 by 5.9 inches), lying unevenly across each other and comes in a variety of types and thicknesses.
OSB is a material with favorable mechanical properties that make it particularly suitable for load-bearing applications in construction. The most common uses are as sheathing in walls, flooring, and roof decking. For exterior wall applications, panels are available with a radiant-barrier layer pre-laminated to one side; this eases installation and increases energy performance of the building envelope. OSB also sees some use in furniture production.
Adjustments to the manufacturing process can impart differences in thickness, panel size, strength, and rigidity. OSB panels have no internal gaps or voids, and are water-resistant, although they do require additional membranes to achieve impermeability to water and are not recommended for exterior use. The finished product has properties similar to plywood, but is uniform and cheaper. When tested to failure, OSB has a greater load-bearing capacity than milled wood panels. It has replaced plywood in many environments, especially the North American structural panel market.
While OSB does not have a continuous grain like a natural wood, it does have an axis along which its strength is greatest. This can be seen by observing the alignment of the surface wood chips.
All wood-based structural use panels can be cut and installed with the same ease and types of equipment used with solid wood.
Health and safety
The resins used to create OSB have raised questions regarding the potential for OSB to emit volatile organic compounds (VOCs) such as formaldehyde. Urea-formaldehyde is more toxic and should be avoided in home use. Phenol-formaldehyde products are considered to be relatively hazard-free. Some newer types of OSB, so-called “New-generation” OSB panels, use isocyanate resins that do not contain formaldehyde and are considered non-volatile when cured. Industry trade groups assert that formaldehyde emissions from North American OSB are “negligible or nonexistent”.