They Don’t Make’em Like They Used To
Who hasn’t heard or often said in frustration, “They don’t make’em like they used to.”
Well, that is literally true with Southern Pine lumber. In July 2011, the Southern Pine Inspection Bureau (SPIB), an agency that sets standards for the grading of Southern Pine lumber, announced that the lumber currently being harvested does not meet the design values for strengths and stiffnesses specified in their design value tables. This has been based on the test results of 2×4 lumber. Larger sizes are being tested and the results will reportedly be available in 2012.
SPIB has stated that some of the design values are reduced significantly, that is, up to 20% or 30%. SPIB has published a new table of design values which is available at their website for 2x4s. This table of new reduced design values has already been approved for 2x4s by the American Lumber Standard Committee (ALSC). SPIB has also published a new table of proposed design values showing reductions for all sizes (2×4 through 2×12). The proposed design values for the other sizes has not been approved by ALSC: they are awaiting further testing, but the suspicion seems to be that the design value for other sizes will also be reduced.
No one has officially stated the reason for the lower values. SPIB states that there is a mix of sources for the lumber. However, it is generally known that design values for all lumbers have been decreasing for years, that is, “they don’t make wood like they used to.” Some point out that today’s lumber is being harvested from new growth forests where the trees have not had the time needed to develop the higher strengths available in the old growth lumber. This makes sense.
The decrease in design values has caused consternation in the wood truss manufacturing industry. The Structural Building Components Association (SBCA), who represents many wood truss manufactures, and others have been in discussions with SPIB and the American Lumber Standard Committee (ALSC) about the significant changes in design values. There are many questions such as: when does this take effect? how does this affect recent past and current design and construction? what design values are to be used? how will this be implemented to avoid confusion and economic hardship?, etc.
As of the writing of this article, the official date of implementation for the new approved design values in the standards referenced by the building codes is June 1, 2012. Some might be inclined to say that those new design values can be ignored until the local jurisdictions adopt the future codes that reference the new standards. However, SPIB and the ALSC state that the June 1, 2012 will allow for an orderly transition, that is, “start using the new design values by June 1, 2012 for 2×4’s.”
ALSC did not make a decision on the new design values for sizes other than 2×4’s, preferring to await test results later in 2012. But in their statement on January 11, 2012, ALSC strongly warned that interested parties use the available information in making decisions about design in the interim.
At PCI we have decided to adopt the new proposed design values until further notice because the indication is that the design values will be lowered for the other sizes also and the lumber being processed at the mills and in storage at the lumber yards is probably the weaker strength lumber.
We hope to have more on this issue as it progresses.