Oriented strand lumber (OSL) is a structural material with very consistent properties from one unit to another, and capable of handling large loads. OSL is produced by aligning long strands of wood in parallel and binding them together using adhesives, pressure and heat. It replaces softwood timber in some residential building applications, but because it can attain dimensions not possible for a single piece of wood it has additional applications in non-residential construction. OSL is also used for industrial purposes, such as in furniture manufacture.
The two most common OSL products available in North America are both proprietary products manufactured by Trus Joist (Weyerhaeuser):
Parallam® PSL (Parallel Strand Lumber) starts with the same wood veneer as is used in the production of plywood and laminated veneer lumber. The veneer is clipped into long strands (up to 8 feet long) that are coated in glue, arranged with their lengths parallel to each other and then pressed into a billet using heat and pressure in a patented microwave process. Douglas-fir is used in Canada and southern yellow pine is used in the U.S.
Parallam® PSL is typically used in beams of up to 7x18 inches and in columns up to 7x7 inches, although custom sizes can also be delivered. For the larger dimensions, steel connectors are normally required. The variability of Parallam® PSL is much less than solid lumber, increasing its load bearing capabilities.
TimberStrand® is produced from strands of wood up to 12 inches long cut from small logs (in a similar manner to the production of oriented strand board) of low-density hardwoods, such as aspen and other poplars. The strands are coated with glue, oriented in parallel and then pressed together in the presence of steam to produce billets smaller than those of Parallam.
TimberStrand® is not as strong as Parallam® PSL, and cannot be produced in sizes as large as Parallam can. However, TimberStrand® has uniform characteristics and good dimensional stability, so that long lengths are unlikely to warp in service. It machines as well as sawn lumber and can be glued with normal wood glues.
Parallam® is currently used in both residential and non-residential construction as headers, beams and columns. It is primarily used to span long distances in structural applications and often replaces steel beams or large timber members.
There are only a few production facilities for these products in North America, and further expansion is not anticipated at this time.
Note: Parallam®, TimberStrand® and Silent Floor® are trademarks of Weyerhaeuser.
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