|Conceptual Reference Database for Building Envelope Research||
OSB - Oriented strandboard
Oriented strandboard (OSB) has been gaining popularity since 1980's in the North America in the construction industry, especially the new residential house sector.
OSB panels are manufactured using residue of wood mill or small-diameter logs that are previously under-utilized. They have a viable potential in time of curtailed timber supplies due to reducing forest, demand from conservation groups and public for saving the environment, and more stringent logging regulations.
OSB panels form a second vapor barrier in the building envelope. The wood stud and insulation, between the vapor barrier on the warm side and OSB on the cold side, have a very low drying potential. This may cause problems related to excessive moisture accumulation. [J. Rao, 1999]
Oriented Strandboard (OSB) is a structural panel that competes directly with softwood plywood in many construction applications. particularly exterior wall and roof sheathing and nearly half of all floor decking. OSB was first produced in Canada in 1964. Since then, capacity has increased steadily, but it wasn¡¯t until the mid 1980s that capacity expanded rapidly. North American production capacity in 1996 was estimated at 15,276 ¡Á 103 m3, nearly twice the 1990 capacity (2). The number of operating mills producing OSB increased by more than 50 percent between 1990 and 1996. This increase in the rate of industry expansion is a direct result of harvest restrictions on West Coast timber. OSB is made from small diameter softwoods and previously underutilized hardwoods and is therefore not dependent on the large diameter logs needed by the softwood plywood industry. West Coast inland mills producing OSB primarily use lodge pole pine logs averaging about 0.25 to 0.3 m (10 to 12 in.) in diameter. compared with the 0.4- to 0.5-m (16 to 20-in.) logs needed for softwood plywood (Table 1). Mills in the South producing OSB use pine plantation thinning and Southern Pine and soft hardwood logs that average about 0.2 m (8 in.) in diameter. Log diameter in the South has gotten smaller. Northern mills rely almost exclusively on aspen logs 0.15 to 0.3 m (6 to 12 in.) in diameter. The diameter of these logs has remained fairly constant. [Spelter, H., McKeever, D., and Durbak, I., 1999]
OSB is not allowed in Europe due to its large chemical emission from the glue in the board.
IRC/NRC measured properties of OSB.
In Europe, there are research projects on both properties measurement and experiments of OSB in use, (in Europe, OSB is chip board)
Increasing permeance of exterior sheathing by OSB and the impact on dry potential.
Reducing the impact of chemical emission from the OSB in building envelope to the indoor environment.
Guidelines for using OSB as exterior sheathing (how it differs from constructions using other panel materials)
Vancouver: The material used for exterior sheathing did not appear to be a major factor. OSB sheathings, which were more commonly used in the total sample, were used on a disproportionately higher number of problem walls with but plywood sheathing was also used in walls that exhibited major problems.
(K. Alan Carlton ) For example, but not limited to, failing to provide an 1/8" gap at ends and edges (between sheets) of Plywood & OSB sheathing, used as flooring, roof & wall sheathing and exterior wall wind bracing.
Fisette, 1997, Choosing between oriented strandboard and plywood :: "Osb and plywood share the same exposure durability classifications: Interior, Exposure 1 (95% of all structural panels), Exposure 2 and Exterior. They share the same set of performance standards and span ratings. Both materials are installed on roofs, walls and floors using one set of recommendations. "
"Logs are ground into thin wood strands to produce oriented strandboard. Dried strands are mixed with wax and adhesive, formed into thick mats, and then hot-pressed into panels. Don¡¯t mistake osb for chipboard or waferboard. Osb is different. The strands in osb are aligned. ¡°Strand plies¡± are positioned as alternating layers that run perpendicular to each other. This structure mimics plywood. Waferboard, a weaker and less-stiff cousin of osb, is a homogeneous, random composition. Osb is engineered to have strength and stiffness equivalent to plywood. -- Fisette, 1997, Choosing between oriented strandboard and plywood ::
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