SBCA Provides Substitution Charts Based on Possible Sept. Design Values

Originally published by: SBCAApril 2, 2012

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The Southern Pine Inspection Bureau (SPIB) Board of Governors had previously issued a full complement of reduced Southern Pine Design values, which can be viewed by clicking the first pdf link below. These values are what SPIB believes will be the end-result of their testing. These are not actual design values. Since these design value are lower than the current published design they could be used in truss design and the end result would be conservative.

A key to understanding these substitution charts is that:

1.     Each chart is designed to allow for an equal to or better substitution. Therefore the published lumber properties are always exactly equal to or higher than the original SP design values. They are blind substitutions.

2.     These design values may be higher than needed in your truss designs. In other words a lower SP design value like the new No. 2 or new No. 1 may work in your truss design just fine. This analysis will need to be performed by each individual truss and wall panel manufacturer for your unique product mix.

Our purpose for publishing these substitution charts follows:

1.     To provide each CM with the information needed to evaluate the impact of the SPIB deemed possible reduction in Southern Pine design values.

2.     To provide an approach to allow those companies that desire to make the transition to lower design values earlier, the opportunity to do so.

From SBCA's point of view, the changes taking place on or around September 2012 can be implemented in the following ways:

1.     Everyone can use the June 1st Southern Pine (SP) Design Values in designs per the SPIB approved “June 1st Supplement #9.”

2.     On or around September 2012 all load carrying member designs will need to focus on the transition to the new SPIB approved SP 2x4 to 2x12 Design Values for all structural end use applications.

3.     Each company should evaluate their use of 2x4 to 2x12 Southern Pine to think through their individual company’s transition to the “New Fall 2012 SP Design Values” between now and the SPIB Supplement #XX effective date.

Please review and study the SP lumber substitution chart that SBCA has assembled for its members by clicking on the second link below. This is intended help buyers and suppliers get a feel for the lumber design values that are directly substitutable for visual and MSR/MEL grades of Southern Pine using all species groups (DF, HF, SPFS & SPF) for all lumber sizes.

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