SBCA Looks at SP Design Value Transition Options
Originally published by: SBCA & SFPA — January 23, 2012
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The Southern Pine Inspection Bureau (SPIB) Board of Governors has issued Supplement #9, which can be view by clicking the pdf link below.
From SBCA's point of view, the changes contained in Supplement #9 can be implemented in the following ways:
- Everyone can use the current Southern Pine (SP) Design Values in designs at the present time per the ALSC January 11, 2012 ruling and the SPIB Supplement #9.
- On June 1, 2012 all load carrying member designs should utilize the new SP No. 2 Design Values for all structural end use applications.
- Each company should evaluate their use of Southern Pine No. 2 to think through their individual company’s transition to the new SP No. 2 Design Values between now and the June 1, 2012 effective date.
One question this immediately raises is, "How can I get similar load-carrying capacities as before?" One option is to specify a larger size and/or higher grade of visually graded SP lumber. Another option is to specify mechanically graded lumber which includes Machine Stress Rated (MSR) and Machine Evaluated Lumber (MEL):
- 2x4 SP No. 2 can be replaced by:
- 2x6 SP No. 2
- 2x4 SP No. 1 Non-dense and better SP visual grades.
- 2x4 MSR/MEL grades shown below:
- These are direct substitutes for 2x4 SP No. 2, but not all of the possible MSR/MEL grades will be produced. The marketplace will eventually determine the most common grades.
- 1500f-1.6ER MSR and M-38 MEL are the closest direct substitutes for the current design values associated with SP No. 2 2x4s.
- 2x4 SP No. 3 and Stud grades can be replaced by:
- 2x6 SP No. 3
- 2x4 SP No. 2 Non-Dense and better SP visual grades
- 2x4 SP MSR/MEL grades shown below:
- These are direct substitutes for 2x4 SP No. 3, but not all of the possible MSR/MEL grades will be produced. The marketplace will eventually determine the most common grades.
- 850f-1.4ER MSR and M-33 MEL are the closest direct substitutes for the current design values associated with 2x4 SP No. 3 and Stud 2x4s.
SBCA continues to believe that all component manufacturers can and should continue to purchase and use SP as they have in the past while working through all the business considerations with respect to a prudent transition or lumber substitution plan.
The design values that currently apply to the other grades of SP can be confirmed at one of the following websites:
- American Wood Council (AWC): http://www.awc.org/calculators/span/calc/timbercalcstyle.asp
- Perform a calculation using SP to see what design values are being used to resist loads currently.
- Southern Forest Products Association (SFPA): http://www.southernpine.com/using-southern-pine_design-values.asp
These lumber industry experts reference the current SP design values for engineering end uses.
SBCA will issue additional bulletins in the near future, setting forth discussion points and further recommendations for truss and component manufacturers directly relating to the current changes and future potential changes to the design values of Southern Pine. All updated information on this issue is posted on SBCA's lumber web site: www.sbcindustry.com/lumber.php.