Southern Pine Industry Meeting Calls for New Standard-Setting Process ~
The Southern Pine lumber industry is grappling with a major new problem concerning visual lumber grade rules and the mechanical strength of Southern Pine dimensional lumber. Based on recent testing, Southern Pine Inspection Bureau, the accredited agency tasked with writing rules and testing lumber, plans to release new, lower strength values for all dimensions of Southern Pine. But some in the industry are arguing for a go-slow approach for setting new design values for all species of wood — and are pushing for a new standard, not just for the wood, but for the standard-setting process itself. Here’s the background: early in 2011, some lumber customers alerted the Southern Pine Inspection Bureau (SPIB), an official industry testing lab and grade-rule writing agency, about performance issues encountered in visually graded Southern Pine wood. Even before the complaints, SPIB had already been routinely testing lumber samples and comparing the test results to the wood’s official published strength characteristics. In that routine testing, however, discrepancies between the measured results and the standard’s minimum had not been wide enough to trigger a full-scale review of the published values. But in 2011, after receiving anecdotal complaints about structural performance of wood in the market, the SPIB undertook a broader effort to test a systematic sample of hundreds of Southern Pine 2x4s, and compare the results of the new testing against the official strength values (numbers which had been originally established by formal testing back in the 1980s and 1990s). SPIB found that the lumber’s industry-wide quality had dropped (at least for 2x4s), and so SPIB has now proposed lowering the published values for tensile strength, strength in bending, and modulus of elasticity of Southern Pine. SPIB’s proposal has set off alarm bells across the industry, and kicked off a controversy about how the lumber industry’s official rule-seting organization, American Lumber Standard Committee (ALSC), should respond to the new data. Lumber distributors, truss makers, and big builders are all worried about the business impact of any change, and particularly of a too-sudden reduction in the allowable design values for the wood they sell or use. Now, one group of industry “stakeholders” is recommending a change in the SPIB’s process for evaluating lumber and grading rules, as well as reform of the ALSC’s formal process for endorsing new rules. Meeting on November 15th and 16th at an Atlanta, Georgia, hotel under the auspices of the Southern Forest Products Association (SFPA), the Southern Pine Design Value Forum produced a working report, “ Findings and Recommendations,” that calls for a do-over of the SPIB’s first round of testing, in order to ensure “sound science” in the testing as well as industry-wide acceptance of the results. As for the new grade rules, the Forum report calls for starting over with a new rulemaking process that would include testing of all sizes and grades of lumber (not just for Southern Pine but also for other species of wood), and would build in longer comment periods and multiple stages of adoption for the standards. The first half of the forum report takes a look at the SPIB’s new test values, along with a similar set of test values measured by Mississippi State University (MSU) researchers. In both sets of tests, the working group pointed out, the vast majority of wood exceeded the grade standard, even taking into account a factor of safety. The official testing protocol allows only 5 percent of a lumber sample to fall below the minimum allowable strength — a very conservative standard. In SPIB’s new testing, 10 percent of the pieces failed below the minimum allowable modulus of rupture. On the other hand, 60 percent of the sample tested at better than double the minimum strength. In Mississippi State’s testing, 6 percent of the test sample failed the test minimum; since the grade standard allows 5 percent to fail, the underperformance in MSU’s sample amounted to just one percentage point. The forum report draws attention to a variety of reinforcing elements that are built into real-world houses, but which are not reflected in the minimums or safety factors used to specify individual framing members. Sheathing, wallboard, partitions, and redundant multiple joists, rafters, or studs all provide buildings with a structural resiliency, stiffness, and strength that serves to augment the capacity of the individual sticks of wood in any typical wood-framed structure, the report notes. Citing a range of published studies that identify reasons to consider the strength standards for framing lumber to be highly conservative, the report concludes, “The preceding discussion documents numerous effects that increase the in-situ performance and safety of light-frame wood structures. These effects go unaccounted for in design, but should not go unrecognized by those evaluating the timeline and impacts of proposed design value changes.” In a second part of the report, the working group sets forth a revised process for modifying official lumber strength values and span tables. Key recommendations include: Revise the numbers once for all lumber sizes, rather than repeatedly for various dimensions of wood; coordinate routine modifications in lumber values with the three-year building code modification cycle, rather than change lumber criteria on a different time cycle; and include a wider cross-section of interested parties (commonly called “stakeholders”) in the SPIB process for selecting and testing wood from the stream of commerce. The authors of the report requested that ALSC and SPIB give careful consideration to their recommendations, “to ensure that sound science prevails, disruptions in the marketplace are minimized, and confidence in the process is restored for all stakeholders.” The ALSC is scheduled to hold a public meeting on January 5 in Washington, D.C., to consider its next steps.
