Recently completed tests of Southern pine select structural grade lumber suggest that more design value changes—usually reductions—are in the works, but they won’t be as severe as they were for visually graded No. 2 2x4s.
The notice issued by the Southern Forest Products Association (SFPA) regarding the work by the Southern Pine Inspection Bureau (SPIB) comes less than two months after some design values were reduced by as much as 30% 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 was done 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 could include a 15% to 25% decrease in bending, changes in tension values of anywhere from a reduction of 150 pounds per square inch (psi) to a 50-psi increase, a 10% drop in compression parallel, and a decrease of up to 100,000 psi for modulus of elasticity. No changes were suggested for shear and compression perpendicular properties, but analysis of the data continues.
SPIB’s technical committee recommended that the bureau’s Board of Governors approve new design vales 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 no change to the current Southern pine specific gravity value of 0.55.
It’s too early in the process to present specific proposed design values, SFPA said. SPIB’s Board of Governors will meet in August to review the proposed design values.
All proposed changes must be submitted to the American Lumber Standard Committee’s (ALSC) Board of Review, which will then hear public comments and vote on whether to 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.