September 1, 2010
SPIB Issues Cautionary Notice On Lumber Grading Values

APPLICATION: Visually Graded Structural Dimension Lumber, 2”- 4” Thick Graded under the Voluntary Product Standard 20 National Grading Rule

The Southern Pine Inspection Bureau has received information that some pieces of lumber have tested lower than the values assigned to the visual grade which were developed through the “In-grade” Testing Program. The information received applies to multiple species and is not limited to Southern Pine. The Bureau has not been provided the data nor the testing protocol used to observe these lower values but we believe the sources to be credible and justify an investigation into this phenomenon.

The Bureau has contacted the USDA Forest Products Laboratory, The American Wood Council, and the American Lumber Standard Committee to begin the process of developing a protocol to determine whether or not properly graded lumber in certain instances might have Fb values below the minimum. Since 1994, (publication of the in-grade design values) the SPIB has conducted an annual resource monitoring program to detect shifts in the resource which would require further examination of the design values. In a 1998 Forest Products Laboratory Research Paper FPL-RP-576 it was noted that: “In general, the results are favorable and do not indicate a significant departure from the results of the original In-Grade testing program or the FPL-64 test program. In fact, the observed MOE tends to be higher than that obtained in either of these programs.” The SPIB and the FPL have been reviewing the results to date, and while the review is not complete, there is not an indication of a shift from the original in-grade test program.

Our investigation will evaluate if there is a need to make some adjustments to either the grading rules or the design values. If consumers of visually graded lumber have immediate concerns and want to pre-empt the possibility of using a piece with lower than needed design values they can take one or more of the following actions:

  • Specify a higher grade
  • Specify a larger dimension
  • Specify Machine Graded Lumber (Machine Evaluated Lumber or Machine Stress Rated Lumber)
  • Avoid “Value Engineered” Construction where individual pieces are subjected to the maximum design stress. Note: Such application already requires a reduction to 90% of assigned values.
  • Do not take the 15% increase in bending stress allowed for three or more repetitive members

The Southern Pine Inspection Bureau will pursue an expeditious review of the efficacy of the American Society of Testing Material design value development procedures and if needed, develop a solution.

Source: The Southern Pine Inspection Bureau, July, 28, 2010

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