The Southern Pine Inspection Bureau (SPIB) issued new design values effective June 1, 2012. The reduction resulted from a systematic, scientifically valid evaluation of strength properties. The roots of this process goes back to the 1920s — today's test protocol of annually testing Southern Pine has been in place since 1990. All species go through similar processes and may experience similar reductions in the near future.
The question for landowners is how does this affect me, my management plan, species selection, etc.? Before we get to that question, let's take an abbreviated look at the net results of this recent action by SPIB.
The only design values that changed on June 1 apply to visually graded SOuthern Pine and Mixed Southern Pine 2x4s and 4x4s that are visually graded #2 or lower. Those sizes and grades not affected include:
• Machine graded # 2 and higher
• Timbers larger than 4x4 and poles
• Laminated beams
• All 2 inch lumber larger than 2x4
• All 2 inch lumber visually (or
otherwise) graded higher than #2
• All Lumber in existing construction
• Radius edge decking
In October, SPIB will present additional testing on the wider demensions to the American Lumber Standards Committee and we can anticipate additional reductions in the "wides." I would guess that the reductions will be somewhat less than those seen in the narrow dimension material (2x4), but that remains to be seen.
In any case, end-using industries such as truss manufacturers, deck builders and home builders can easily adjust for reduced values by design, that is, by using a higher grade (or a larger piece) and by slightly reducing spans in the case of joists and rafters.
As a species, Southern pine remains among the top in terms of strength, hardness, treatability and sustainability.
In a recent webinar by the Southern Forest Products Association, Kathy Marx, VP, SFPA, stated that the reasons for the changes in lumber strength were not studes but said that "some experts attributed the changes 1) to the move to loblolly pine - versus long leaf and slash
and 2) changes in the manufacturing process." However, there is no hard science nor studies to back up these assumptions.
So, is this an alarm, or business as usual? I lean toward the latter, and I think most professional foresters would advise landowners to continue with proven silvicultural practices such as varietal seedlings, appropriate site preparation and herbicide control when necessary.
Growing genetically improved stock with better form, survival rates, disease resistance, smaller branches resulting in smaller knots, combined with faster growth and improved density is a "no-brainer" regardless of what happens with lumber manufacturers and their product's end uses.
The bottom line: Stay the course, keep doing all the rights things. This combined with a large measure of patience will result in handsome profits when the housing situtal returns to a reasonable level.
The complete webinar on Southern Pine Lumber strength issue an be seen on YouTube: