Oriented strand board (OSB) is a type ofengineered wood, formed by addingadhesives and then compressing layers ofwood strands (flakes) in specific orientations. It was invented by Armin Elmendorf in California in 1963.[1] OSB may have a rough andvariegated surface with the individual strips of around 2.5 cm × 15 cm (1.0 by 5.9 inches), lying unevenly across each other, and is produced in a variety of types and thicknesses.
Oriented strand board is sometimes confused withchipboard, a synonym forparticle board, whose "chips" are of a size that a lay person would likely describe as "particles".
OSB's mechanical properties make it suitable for load-bearing applications inconstruction.[2] In North America, it is more popular thanplywood, commanding 66% of the structural panel market in 2016.[3] The most common uses are assheathing in walls, flooring, and roof decking. For exterior walls, panels are available with aradiant-barrier layer laminated to one side; this eases installation and increases energy performance of thebuilding envelope. OSB is also used infurniture production.
Oriented strand board is manufactured in wide mats from cross-oriented layers of thin, rectangular wooden stripscompressed and bonded together withwax and syntheticresinadhesives.
The adhesive resins types used include:urea-formaldehyde (OSB type 1, nonstructural, nonwaterproof);isocyanate-based glue (orPMDI poly-methylene diphenyl diisocyanate–based) in inner regions withmelamine-urea-formaldehyde orphenol formaldehyde resin glues at surface (OSB type 2, structural, water resistant on face); phenol formaldehyde resin throughout (OSB types 3 and 4, structural, for use in damp and outside environments).[4]
The layers are created by shredding the wood into strips, which are sifted and then oriented on a belt orwire-mesh caul (a heated, ventilated support) and coated with the resin.[5] The layers thus built up are transferred to a forming line and cross-oriented so that strips on the external layers are aligned to the panel's strength axis, while the internal layers are perpendicular.[6] The number of layers placed is determined partly by the thickness of the panel, and is limited by the equipment used. Individual layers can also vary in thickness to give different finished panel thicknesses; typically, a 15 cm (5.9 in) layer will produce a 15 mm (0.59 in) panel thickness[citation needed]. The mat is placed in a thermal press to compress the flakes and bond them by heat activation and curing of the resin. Individual panels are then cut from the mats into finished sizes. Most of the world's OSB is made in the United States and Canada in large production facilities.
Materials other than wood have been used to produce products similar to OSB.Oriented structural straw board is an engineered board made by splitting straw and formed by adding P-MDI adhesives and then hot compressing layers of straw in specific orientations.[7] Strand board can also be made frombagasse.
In 2005, Canadian production was 10,500,000 m2 (113,000,000 sq ft) (3⁄8 in or 9.53 mm basis) of which 8,780,000 m2 (94,500,000 sq ft) (3⁄8 inch) were exported, almost entirely to the United States.[8] In 2014,Romania became the largest OSB-exporting country in Europe, with 28% of the exports going toRussia and 16% toUkraine.[9]
Adjustments to the manufacturing process can affect thickness, panel size,strength, andrigidity. OSB panels have no internal gaps or voids, and can be water-resistant, although they do require additionalmembranes to achieve impermeability to water and are not recommended for exterior use. The finished product has properties similar toplywood, but is uniform and cheaper.[10] When tested to failure, OSB has a greater load-bearing capacity than milled wood panels.[11] It has replaced plywood in many environments, especially the North American structural panel market.
All wood-based structural use panels can be cut and installed with the same types of equipment as for solid wood.
The resins used to create OSB have raised questions about their emission ofvolatile organic compounds such asformaldehyde,[12] although industry trade groups assert that formaldehyde emissions from North American OSB are "negligible or nonexistent".[13]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" panels, useisocyanate resins that contain no formaldehyde and are considered nonvolatile when cured.[14]
Some manufacturers treat the wood chips with variousborate compounds that are toxic totermites, wood-boringbeetles,molds, andfungi, but notmammals in applied doses.
In 2024, a hotel inDublin, Ireland, lost itsfire safety certificate after an inspection found fault with the composition of OSB in its flooring and walls.[15]
Five grades of OSB are defined in EN 300 in terms of their mechanical performance and relative resistance to moisture:[2]
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