Oriented strand board ( OSB ) consists of strands of wood with widths typically half their length bonded using phenol-formaldehyde resin to create board thicknesses in the range 6-38 mm. There is always some general alignment of the strands, which creates anisotropic board properties. Compliance with the Construction Products Directive must be demonstrated when used for construction, and this may be achieved through compliance with the European Harmonised Standard for wood-based panels, EN 13986 ( or BS EN 13986 in the UK ). The UK standard refers to BS EN 300, which classifies OSB into four grades according to loadbearing capacity and moisture resistance. About 90% of OSB is used in construction, mostly in load bearing situations. It is used as sheathing in timber frame housing and as roof decking material, and to a lesser degree as flooring. Alternative design procedures for structural use applications are briefly discussed. These are performance testing, and design by calculation using permissible stress design or limit state design.