A. Cathy Kaake, senior director of engineered and framing markets at the Southern Forest Products Association (SFPA), responds: Based on recent tests of visually graded 2x4 lumber, the Southern Pine Inspection Bureau (SPIB) made several changes to its 2002 rule for grading southern pine lumber. The new rule reduces some design values for bending (Fb), tension parallel to grain (Ft), compression parallel to grain (Fc), and modulus of elasticity (E and Emin). Included in this change are the four main species of loblolly, longleaf, shortleaf, and slash pine, as well as mixed southern pine. The SPIB didn't study the reasons for the change in strength revealed in the tests, but it may be due to changes in forestry management practices.
So far, the change affects only 2x2s, 2x3s, 2x4s, 3x3s, 3x4s, and 4x4s in No. 2 and lower grades. The revised design values will become effective June 1, 2012.
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