The Science Behind the Strength

Using solid sections reduces the labor and cost of fastening a multiple member together

September 30, 2015
engineered lumber framing in new construction

Engineered for consistent performance, Parallam® Parallel Strand Lumber is one of the strongest engineered wood products available. This post examines the science behind the product, and why it’s such a reliable long-span, heavy load beam solution.

Manufactured in Delta, British Columbia and Buckhannon, West Virginia, Parallam is made primarily from Douglas fir in the west and yellow poplar/southern yellow pine in the east. Once harvested, the logs are debarked and peeled into veneers from which they are cut into strands. Adhesive is applied to the dried strands and then they are aligned in a trough prior to manufacturing the Parallam PSL billet. A microwave press then cures the adhesives. Finally the product is cooled and cut to the final sizes.

Parallam PSL is manufactured into solid sections with widths of 3.5”, 5.25” and 7” and depths up to 18”. Using solid sections reduces the labor and cost of fastening a multiple member together. In addition, the solid section has greater lateral stablility than a typical built up member. This increased stability may reduce the amount of required compression edge bracing. Additionally, the solid section (in specific sizes) can be utilized as heavy timber construction as allowed in the International Building Code (IBC).


Beam, Column and Header Grades

Parallam PSL is manufactured in 1.8E, 2.0E and 2.2E grades, depending on the region it is produced in (and ultimately sold in) and the typical end use application. 1.8E Parallam PSL is designated as columns in our literature and is available in 3.5”, 5.25” and 7” widths and depths up to 7”. Being one solid piece, Parallam PSL used as a column will provide a very high vertical load capacity without the question of how to fasten it together like one has with built-up members (see Built-Up Column Conundrum blog for more on this). Because the columns are the same dimensions as our engineered wood beams, the columns provide full width bearing to the beams above, possibly eliminating the need for expensive column caps. But don’t let the label ‘column product’ limit its use. 1.8E Parallam PSL can be used in beam and header applications as well, see ESR-1387 for design properties or download Forte, our free single member sizing software, where it can be sized in horizontal orientation as a header or beam.

2.0E/2.2E Parallam PSL is typically considered a beam product due to the larger depths available (3.5”, 5.25” and 7” widths and depths up to 18”) which are ideal for long spans and heavy loads. 2.2E product is a regional product stocked in the Pacific Northwest (California, Oregon and Washington State) and Western Canada only.  Just as with the 1.8E product, don’t let the label ‘beam product’ limit its use, it can be used as a column as well. Technical bulletin TB-604 was produced to give specifiers a quick reference guide for 2.0E/2.2E Parallam PSL used as a column where a very high load capacity is required. Our beam products specifier guide, TJ-9000, is also great resource for available sizes, grades, design properties and span charts.


Exterior Solutions

For applications such as exterior decks, or other areas where resistance to termites and fungal decay is required, we offer Parallam Plus PSL. The product is made from southern yellow pine and is treated at Weyerhaeuser-authorized treating facilities in partnership with Arch Wood Protection, Inc. It is kiln-dried after treatment and is backed by a 30-year limited warranty. The column products are treated with CCA to a retention level that allows for ground or fresh water contact, as well as salt water splash (use category 4B (UC4B) per the American Wood Protection Association (AWPA) use category system). Beam products are treated with Copper Azole (CA-C) and are acceptable to be used in applications defined by use category 4A (UC4A) per the AWPA. Due to the treatment differences, beam products may not be appropriate for column applications. Our specifier guide TJ-7102 discusses in further detail the available sizes, use category definitions as well as providing framing and cladding details along with an extensive Q&A on the product. In addition, the blog ‘What’s so special about Parallam® Plus PSL’ provides an in-depth review of the product.

For projects in flood prone areas, including coastal construction zones, Weyerhaeuser has developed two technical bulletins to educate and assist the design community in meeting various construction requirements. TB-213 discusses in depth the requirements for flood damage-resistant material. TB-217 discusses the use of Parallam Plus PSL in coastal construction (and reconstruction), including design and detailing for beam to pier construction.

With its unique grain and appearance, Parallam PSL has been the choice for many non-traditional applications. Everything from shelving, stair treads, table tops to exposed members that add an exotic look to a project, Parallam PSL might be the answer for your unique application.


Jerad Bankston, P.E. is a Weyerhaeuser engineer supporting Trus Joist Engineered Wood Products who is based out of St. Paul, Minnesota. During his 11+ years with Weyerhaeuser, Jerad has provided technical support for residential, multifamily and industrial applications.