Lumber Design Values

No matter the species, component manufacturers (CMs) purchase and 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, floor or roof truss) and a lumber 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. For that reason, SBCA believes accurate lumber design values are vital to the success of the industry.

Top Resources

This article puts lumber design values into layman’s terms and walks the reader through the reasons why component manufacturers don’t purchase lumber, they purchase design values.

This article explores the potential risk component manufacturers assume in using visually-graded lumber now that the American Lumber Standards Committee has updated their PS 20 grading rule.

On August 1, 2013, the Board of Directors approved the Structural Building Components Industry Truss and Component Raw Material and Construction Products Design Properties Policy.

This article takes a chronological look at the 2012 SYP design value change and explores the ways SBCRI testing capabilities potentially saved component manufacturers from millions of dollars in losses.

Best Practices

SBCA has created a series of truss design drawing notes to help component manufacturers mitigate risk by establishing a clear scope of work with relation to visually graded lumber design values.

SBCA has put together a series of online tools to help component manufacturers navigate lumber design value changes.

SBCA provides best practice guidance to component manufacturers on how to successfully navigate a lumber design value change.

SBCA outlines how machine rated lumber is not affected by design value changes that impact visually graded lumber. For this reason, MSR/MEL may sometimes be a preferable raw material.