By Art Lewis, P.E.
Parallam® Plus PSL, our preservative-treated version of Parallam® PSL, has built an outstanding reputation of resisting adverse weather and climates while performing structurally as a beam or column member. What makes this product so durable for exposed exterior applications?
The stranded composition of Parallam® PSL creates numerous small voids in the member cross section. Those voids allow for penetration of the waterborne preservatives through the entire member versus “envelope” treatment of solid-sawn timbers. Thorough treatment provides the basis for the 30-year limited warranty from Arch Wood Protection, Inc. for durability against termites and fungal decay.
Parallam® Plus PSL members are manufactured by Weyerhaeuser plants uniquely for the treatment process. Parallam® Plus PSL is made from southern pine, a wood species known for its treatability, and cut to smaller dimensions than standard Parallam® PSL. The smaller dimensions and a proprietary kiln drying process result in an “in-service” size near the nominal member dimensions. Allowance for that cross-sectional growth normal with the treating process can be critical where hangers are concerned or the member has to match other product depths.
Every Parallam® Plus PSL member is stamped with the product description, type of treatment, and other related info to verify the proprietary treatment process was followed (a key component of the 30-year warranty).
“Standard” Parallam® PSL may contain wood species that don’t readily accept the treatment chemicals. This is important because limited treatment retention means that product may deteriorate prematurely. Additionally, finished product sizes from Weyerhaeuser plants are targeted at nominal member dimensions. “Standard” Parallam® PSL will likely be oversized if treated and may exhibit poor performance due to excessive dimensional change after installation.
In summary, Parallam® Plus PSL performance and warranties can’t be gained simply by treating standard Parallam® PSL, due to the many special steps in the manufacturing and treatment process. It has to be the genuine product. To learn even more about Parallam® Plus PSL, visit the product page on our website or reference the Parallam® Plus product literature Eastern Edition or Western Edition.