Authorities may come to a final decision this month about new design values for Southern Pine lumber. In a meeting scheduled for January 30, the American Lumber Standards Committee (ALSC) appears poised to make a final decision about the engineering design values assigned to visually graded Southern Pine lumber, which will result in new published span and load tables for the species.
The new, lower strength values will have an immediate effect for producers of engineered products such as floor and roof trusses. As codes adjust over time to reflect the new values, framers and deck builders will also be affected — especially if they build with pressure-treated wood, which (at least in the Eastern U.S.) is mostly Southern Pine.
Southern Pine has been under study for several years: after engineers at sawmills and truss makers noticed an apparent decline in the lumber’s strength, the industry has been working to systematically test lumber from a range of mills across the Southern Pine growing region. That testing indicated that average lumber strength has dropped, but technical issues have delayed the creation of new official values for the lumber properties used by engineers to design structures. Now, those wrinkles have been ironed out, and action on the new design values appears to be imminent.
The Southern Pine Inspection Bureau (SPIB) is a non-profit agency tasked with determining grade rules for Southern Pine lumber and conducting quality control inspections for grade-stamped lumber from mills across the South. SPIB has conducted a full round of testing on Southern Pine 2x4, 2x8, and 2x10 lumber samples from the whole region in the past year, as required by the American Softwood Lumber Standard (PS 20) and by ASTM Standard D1990.
In October, SPIB submitted new proposed design values to the ALSC, which has to approve any change. But under the national standard, the USDA Forest Products Laboratory is required to review any grade rule changes; and in this case, FPL had a few minor quibbles with the way SPIB came up with its numbers. So SPIB withdrew its proposal, and worked with FPL to resolve the discrepancies. Now, the differences have been reconciled; SPIB has sent a revised proposal to the ALSC, and FPL has indicated that its engineers are also satisfied with the methods and results.
Here’s a little history on the Southern Pine story. SPIB first alerted the lumber industry to strength concerns back in July 2010. After a preliminary testing program involving only 2x4 #2 samples, SPIB concluded that the lumber had indeed gotten weaker, and recommended an across-the-board downgrade of all grades and dimensions of Southern Pine in the fall of 2011. But based on its reading of the Softwood Lumber Standard and the ASTM D1990 rule, ALSC declined to lower the values for any dimensions other than the 2x4 size and #2 grade that SPIB had actually tested. Instead, ALSC directed SPIB to continue with an industry-wide testing program for other sizes and grades.
That further testing uncovered good news. While larger dimensions, such as 2x10 and 2x12 used for joist and rafter framing have indeed gotten weaker, the downgrade in those larger sticks is not as severe as in the 2x4 and 2x6 lumber. So for applications such as deck framing or roof framing, Southern Pine continues to be competitive with other lumber on the market, such as eastern spruce, pine, and fir (sold in a combined grade called S-P-F), or Western hemlock and fir (graded and marketed as Hem-Fir). The Southern Forest Products Association, an industry association representing lumber producers in the South, posts information on its website that helps lumber consumers compare their options.
Rubin Shmulsky heads up the Forestry Department at Mississippi State University, and has been involved in the industry discussion about Southern Pine grading. Coastal Connection talked with Shmulsky this week. "It looks to me like when ALSC meets in January, SPIB will propose these new values in all the sizes."
And Shmulsky said that the strength downgrade will make a difference for builders in the field. "The new values are going to be conservative," he said. "They’re certainly lower — it’s a reduction. But they’re not as low as they would have been based on SPIB’s initial proposal."
The lower values will have an effect on lumber users, and on producers. "The new values do affect what a 2x10, for example, will span," Shmulsky said. "Previously, a 2x10 joist on 16-inch spacing would span 16 feet, and it no longer does. And in anticipation of that, mills have been cutting and selling a lot of 2x12s — the mills that can cut those, that is."
"My hope is that the new policy will require SPIB to re-test every few years," said Shmulsky. "Some of the feedback that we are getting from lumber mills is that this time, they did testing based on old standards and existing protocols and they found that there is some reduction in strength, and that makes it so that you can’t span as far with any given size or grade. But we’ve got a chance now to try to open up the protocol, and that’s something that we’re going to try to do — re-evaluate, do we still need to sample and test the wood the same way we did 30 years ago? Or should we try to update it somewhat? And if we can get the sampling and testing updated, then in the next testing, which may happen three years from now, I think we can get even more reliable numbers."