SBCA Launches Lumber Design Value Article Series

While it may seem obvious to some in the industry, it’s important to highlight the fact that component manufacturers (CMs) do not simply purchase lumber for use in their products. More accurately, they purchase and rely on the design values attributed to that lumber. Understanding that subtle difference is key to understanding how the structural building component industry utilizes wood. 

No matter the lumber species, CMs rely on the accuracy and reliability of many different lumber design properties, including: bending (Fb); shear parallel to grain (Fv), compression perpendicular to grain (Fc ⊥), compression parallel to grain (Fc), tension parallel to grain (Ft), and modulus of elasticity (E and Emin). Depending on the type of component (roof or floor truss), and a wood member’s location in that component (top chord, bottom chord, or web), one or more of these design values are critical to the structural performance of that component and will control the ability of the lumber member to resist anticipated loads and meet the serviceability requirements over the life of a structure. 

The characteristics of what we know as softwood lumber is determined through the American Softwood Lumber Standard, also known as Voluntary Product Standard PS 20. PS 20 applies to domestic lumber production consumed in (and exported from) the United States, as well as lumber imported into the United States.  It is developed and maintained by the American Lumber Standard Committee (ALSC).  The ALSC’s Board of Review (ALSC BOR) operates as an independent body and certifies grading rules, approves design values, accredits agencies to grade and inspect structural lumber as defined in PS 20.  Similarly, Canada’s National Lumber Grades Authority (NLGA) is responsible for the establishment, issuance, publication, amendment, and interpretation of Canadian lumber grading rules and standards. 

Within the grading rules established by ALSC and NLGA, there is a lot to unpack to fully appreciate how the organic properties of different species of trees grown throughout North America (and the world) translate into reliable design values. That is why SBCA is launching an article series that will walk through everything from common North American softwood species groups to grade stamps and what they communicate.  In addition to the nuts and bolts of design values, this series will also touch upon best practices for purchasing and receiving lumber, as well as exploring the impacts of lumber species/grade substitution.