Early analysis of recently completed testing of Southern pine select structural grade lumber suggests that Southern pine design value changes may expand beyond visually graded No. 2 2x4s.
Today’s announcement by the Southern Forest Products Association (SFPA) comes less than two months after design value changes were implemented for visually graded No. 2, and lower, 2x4s. The recent testing completed the fully in-grade testing matrix and involved select structural 2x4s and both select structural and No. 2 2x8s and 2x10s.
Testing included bending, tension, and compression and was completed by the Southern Pine Inspection Bureau (SPIB) in cooperation with Timber Products and with technical oversight provided by the U.S. Department of Agriculture’s Forest Products Laboratory.
The SPIB Technical Committee met on July 18-19 to review the results. "The preliminary data analysis suggests smaller reductions for the wider widths and higher grades as compared to the No. 2 2x4s, and even some small increases as compared to current design values," SFPA said.
According to the test results, approximate design value changes for all visually graded 2x6s through 2x12s include a 15% to 25% decrease in bending, a -150 poundes per square inch (psi) to +50 psi change in tension, a 10% decrease in compression parallel, and a decrease of up to 100,000 psi for modulus of elasticity. There are no changes be suggested for shear and compression perpendicular properties. These values are subject to change as analysis continues.
Following its meeting, the technical committee recommended to the SPIB Board of Governors that the board approve all new design values for visually graded Southern pine, including dense and non-dense grades, and that prime grades continue to have the same design values as their corresponding dimension lumber grades. The committee also recommended that there be no change to the current Southern pine specific gravity value of 0.55.
The SFPA said it is too early in the approval process for the presentation of specific proposed design values. According to the SFPA's announcement, the SPIB Board of Governors will meet in August to approve the proposed design values.
As a rules-writing agency, SPIB must follow a rigorous approval process to establish new design values. All proposed changes must be submitted to the American Lumber Standard Committee’s (ALSC) Board of Review, which will then open public comments and vote on whether the approve the changes.
The ALSC is a quasi-governmental agency that sets grading and quality standards for all lumber used in residential construction. Its Board of Review approved the design value changes for No. 2 and lower 2x4s on Jan. 11. Those changes took effect on June 1.