A Look Back: The Evolution of Southern Yellow Pine Span Table

[jar546]

A Look Back: The Evolution of Southern Yellow Pine Span Tables​

Introduction​

In the realm of construction and building codes, few events have had as profound an impact as the revision of the Southern Yellow Pine (SYP) span tables in the early 2010s. This article takes a retrospective look at this significant development, tracing its origins, the process of change, and its implications on the building industry.

The Prelude to Change​

Southern Yellow Pine has long been a staple in American construction, prized for its strength and versatility. However, changes in forestry practices led to variations in the wood's characteristics. By the early 2000s, it became evident that the newer SYP did not possess the same density and strength as its older counterpart, primarily due to faster growth rates and a resulting looser grain pattern.

The Turning Point: 2013 Design Value Revisions​

The critical turning point came with the Southern Pine Inspection Bureau's (SPIB) comprehensive testing and subsequent publication of new design values in 2013. This rigorous process, which adhered to the consensus standard ASTM D1990, involved destructive testing of more than 7,400 full-size samples of commercially produced SYP.

On February 11, 2013, SPIB published Supplement No.13 to the 2002 Standard Grading Rules for Southern Pine Lumber, encompassing new design values for all sizes and grades of visually graded SYP lumber. These changes were officially approved by the Board of Review of the American Lumber Standard Committee following a hearing on January 30, 2013.

Implementation and Impact​

The new design values became effective on June 1, 2013, marking a significant shift for the building industry. This included a 20 to 30 percent reduction in key design values such as bending, tension parallel to grain, compression parallel to grain, and modulus of elasticity.

The Southern Forest Products Association (SFPA) was instrumental in facilitating this transition. They released an updated set of span tables on July 24, 2013, which included comprehensive listings for maximum spans for SYP joists, rafters, headers, and beams.

Response and Adaptation​

The building industry had to adapt quickly to these changes. For instance, in North Carolina, the new design values were incorporated into the 2012 NC Residential Code, effective from January 1, 2015. This adaptation was crucial to maintain safety standards and reflect the evolving characteristics of SYP lumber.

Conclusion​

The revision of the SYP span tables stands as a pivotal moment in building history, underscoring the dynamic nature of construction materials and the need for continuous evaluation and adaptation of building codes. This episode serves as a reminder of the interplay between natural resources, industrial practices, and regulatory standards, shaping the built environment we inhabit.

 

[Yankee Chronicler]

The same thing happened with Douglas Fir back in the last century. When I started out as an intern architect, Douglas Fir was considered THE premier framing lumber species in the northeast.

And then new grading standards and span tables were issued, also as a result of the lack of old growth forests and the fact that newer, fast growth wood isn't as strong, and all of a sudden one day we awoke to find that magically Hem-Fir joists, grade-for-grade, could (according to the tables) span longer distances than good old Douglas Fir. And sometimes the differences were significant.

Now that we're in the 21st century, things have settled down a bit and the difference between Douglas Fir and Hem-Fir isn't as great as it was, but this phenomenon affected all species at one time or another.

 

[jar546]

The same thing happened with Douglas Fir back in the last century. When I started out as an intern architect, Douglas Fir was considered THE premier framing lumber species in the northeast.

And then new grading standards and span tables were issued, also as a result of the lack of old growth forests and the fact that newer, fast growth wood isn't as strong, and all of a sudden one day we awoke to find that magically Hem-Fir joists, grade-for-grade, could (according to the tables) span longer distances than good old Douglas Fir. And sometimes the differences were significant.

Now that we're in the 21st century, things have settled down a bit and the difference between Douglas Fir and Hem-Fir isn't as great as it was, but this phenomenon affected all species at one time or another.

I will still take doug fir over syp any day of the week. I am in the south now and it sucks. Everything is syp.

 

[Paul Sweet]

This was actually the second downgrading of visually graded Southern Pine strengths. Originally clear 2-inch by 2-inch by 30-inch specimens were tested and strengths for different visual grades were a percentage of this strength. In 1991 Southern Pine strengths were reduced depending on the depth of a member, based on In-Grade testing of full-size samples of commercially produced lumber.

I've always specified Fb = 1200 PSI and E = 1,500,000 PSI. #2 SP met these strengths before 1991. After 1991 I had to change my specs to #2 Dense or #1 to achieve these strengths. Now I have to specify #1 (Select Structural for 2 x 12).