Parallel strand lumber (PSL) is a high strength structural composite lumber product manufactured by gluing strands of wood together under pressure. It is a proprietary product marketed under the trade name Parallam®.
Because it is a glued-manufactured product, PSL can be made in long lengths but it is usually limited to 20m (66 ft.) by transportation constraints.
Manufactured at a moisture content of 11 percent, which is approximately the equilibrium moisture content of wood in most service conditions, PSL is less prone to shrinking, warping , cupping, bowing or splitting.
It is manufactured in Canada from Douglas fir and in the United States from southern pine from wood strands from which the growth imperfections have been removed. This results in a product having consistent properties and high load carrying ability. As smaller plantation and second growth timber finds its way into the market place to a greater extent, PSL provides a means of ensuring the availability of a large dimension and high quality wood product.
The manufacturing process for PSL results in a strong, consistent material that is resistant to seasoning stresses.
PSL is well suited for use as beams and columns for post and beam construction, and for beams, headers, and lintels for light framing construction.
It is commonly used for heavily loaded columns, and beam and header applications where high bending strength is needed.
Visually, PSL is an attractive material which is suited to applications where finished appearance is important. It is also suited to concealed structural applications where appearance is not a factor.
PSL readily accepts preservative treatment and a very high degree of penetration and therefore protection is possible. Treated PSL should be specified for members which will be directly exposed to high humidity conditions.