Effective June 1, 2012, the Southern Pine Inspection Bureau (SPIB) has issued some new design values for Southern Pine Lumber. The changes will affect only visually graded Southern Pine and Mixed Southern Pine sized 2” to 4” wide and 2” to 4” thick (2x2s through 4x4s) in No.2 and lower grades (No.2, No.3, stud, construction, standard and utility). This also includes new design values for No.2 dense and No.2 nondense Southern Pine. Design values for all other grades and sizes of visually graded Southern Pine remain the same, pending results of testing scheduled for completion later this year.
The last major change for visually graded dimension lumber occurred in 1991 when design values for Southern Pine and other North American species were published based on In-Grade testing of full-size samples of commercially produced lumber. Since 1994, SPIB has conducted an annual resource-monitoring program developed in collaboration with the U.S. Forest Products Laboratory (FPL). SPIB is the first rules-writing agency to publish new design values. Rules-writing agencies responsible for other species are in different stages for evaluating design values.
Design values for structural lumber undergo a rigorous approval process. SPIB partnered with Timber Products Inspection to sample No.2 2x4 test specimens according to a plan approved by the American Lumber Standard Committee (ALSC) Board of Review. SPIB and Timber Products conducted destructive tests in bending and tension, plus gathered stiffness and property data, all in accordance with ASTM International standards. Throughout the process, technical review was performed by FPL. The ALSC Board of Review approved the new design values early in 2012 with a recommended effective date of June 1, 2012.
As June 1 approaches, users should begin using the new design values and revised span tables if they haven’t done so already. The intent of the six-month transition period was to minimize project delays and supply chain disruptions by providing time to begin to use the new design values or switch to other Southern Pine grades or sizes meeting performance requirements. Southern Pine users have many available product options, including visually graded dimension lumber and an increasing supply of mechanically graded lumber. Many producers and key customer groups have already successfully transitioned to the new design values with minimal disruption to their businesses.
Building codes reference design values are certified by the ALSC Board of Review. The American Wood Council (AWC) publishes these design values in a supplement to the code-referenced National Design Specification (NDS) for Wood Construction. Building codes also include span tables and other prescriptive requirements that will need to be amended to reflect the new design values. Visit AWC.org to download the AWC Addendum to Design Values for Wood Construction, revised prescriptive span tables and other updates to AWC’s standards and design tools. Also visit Southernpine.com to obtain easy-to-use span tables for specific grades and sizes of Southern Pine lumber.
SPIB and timber products are currently working to complete the full In-Grade matrix by destructively testing No. 2 select structural 2x4s, 2x8s and 2x10s in bending, tension and compression. Additional design value changes are expected once all the testing is completed later this year. Moving forward, Southern Pine will continue to be monitored with annual destructive testing.