How APA Built a Competitive Advantage for OSB Through the Building Code

Originally published by: SBCRI-SBCA Investigative Report #1October 15, 2015

The following article was produced and published by the source linked to above, who is solely responsible for its content. SBC Magazine is publishing this story to raise awareness of information publicly available online and does not verify the accuracy of the author’s claims. As a consequence, SBC cannot vouch for the validity of any facts, claims or opinions made in the article.

SBCRI's goal is to ask: Is this true or not? SBCRI provides the facts and lets the reader decide.

As shown below, IRC code-compliant math establishes as law the following design values for isolated (a.k.a intermittent) braced wall panels:

  • 350 plf = 600 plf for isolated braced wall panels without gypsum wallboard
  • 450 plf = 840 plf for isolated braced wall panels with gypsum wallboard

This codified math provides a significant competitive advantage for the OSB products of APA-The Engineered Wood Association members.


Why is this math part of the IRC?

Let's answer that question, using the facts and SBCRI test results. First, some background.

Background: Definitions

R602.10 Wall bracing.
Buildings shall be braced in accordance with this section or, when applicable, Section R602.12. Where a building, or portion thereof, does not comply with one or more of the bracing requirements in this section, those portions shall be designed and constructed in accordance with Section R301.1.

R602.10.2 Braced wall panels.
Braced wall panels shall be full-height sections of wall that shall have no vertical or horizontal offsets. Braced wall panels shall be constructed and placed along a braced wall line in accordance with this section and the bracing methods specified in Section R602.10.4.

R602.10.2.2 Locations of braced wall panels. 
A braced wall panel shall begin within 10 feet (3810Â mm) from each end of a braced wall line as determined in Section R602.10.1.1. The distance between adjacent edges of braced wall panels along a braced wall line shall be no greater than 20 feet (6096 mm) as shown in Figure R602.10.2.2.

The following figure shows intermittent (also known as isolated) braced wall panel construction where R602.10.2 Intermittent braced wall panel construction methods says that the construction of intermittent braced wall panels shall be in accordance with one of the methods listed in Table R602.10.2. 

The minimum code requirements for braced wall panel and braced wall line framing is found in IRC R602.10, where walls are constructed as follows:

  • SPF studs spaced 16" o.c.
  • Anchor bolts holding the wall down. (i.e. not hold down connection like HDU8s, which are then called segmented shear walls).
  • 3/8" wood structural panels (i.e., OSB) with the grade defined in IRC R604.1.
  • Nails applied 6" o.c. along the edges and 12" o.c. in the field.
  • Nail edge distance a minimum of 3/8 inch.
    • The APA recommends a 1/8" gap for OSB swelling. This is not a code requirement, but it does have a direct effect on code compliance given the need for a 3/8" edge distance to maintain braced wall design resistance. More on this issue in another of our SBCRI-SBCA Investigative Reports.
  • Fastener type per exterior sheathing requirements found in Table R602.3(3) as follows:

Background: Isolated Braced Wall Panel Ultimate Strength Values from the IRC

As defined by Crandell and APA’s Martin in “The Story Behind IRC Wall Bracing Provisions, Parts 1 & 2 - Crandell/Martin [pdf]”, the IRC assigns the following ultimate strength properties to isolated braced wall panels.

  • 350 plf = 600 plf for isolated braced wall panels without gypsum wallboard
  • 450 plf = 840 plf for isolated braced wall panels with gypsum wallboard

A May 2007 APA test report created for the Building Seismic Safety Council (BSSC) provided the following ultimate strength (i.e. peak load) properties for the IRC application above:

  • 351 plf for isolated braced wall panel without gypsum wallboard

  • 383 plf for isolated braced wall panel with gypsum wallboard

APA’s test data evaluation suggests that OSB has the following ultimate strength values for braced wall panels as defined in the IRC:

  • 351 plf for an isolated braced wall panel without gypsum
  • 383 plf for an isolated braced wall panel with gypsum

The APA report containing this evaluation can be found here  A Review of Large Scale Wood Structural Panel Bracing Tests - APA Staff (Martin, Skaggs, Keith, Yeh [pdf]). This testing is a compilation of test reports from various sources using various testing techniques.


What did SBCRI find?

SBCRI undertook proprietary testing using ASTM E564 techniques (i.e. shear resistance of framed walls for buildings) in an ASTM E2126 cyclic testing environment.The testing was performed in a manner that replicates precisely the IRC isolated braced wall panels in a braced wall line in a real building using anchor bolts (i.e. this test was pure IRC not the segments shear walls of the IBC or SDPWS. More on that in another article as similar issues exist there). This testing found the ultimate strength properties to be:

  • 350 plf for SBCRI isolated braced wall panels without gypsum wallboard
  • 450 plf for SBCRI isolated braced wall panels with gypsum wallboard

The testing was conducted at SBCA using a 12x30 foot, code-compliant, full-building test, as the following photos show:

The ultimate strength values that have been generated by SBCRI are based on tests that were reported on in 2013 and test data that has been added to the SBCRI OSB benchmark database as new benchmark testing is undertaken. 

The SBCRI testing confirms the APA BSSC report ultimate strength values and provides greater confidence that the SBCRI testing accurately reflects real building performance.

The IRC code-compliance math assigns, by law, the following OSB design values:

  • 350 plf = 600 plf for isolated braced wall panels without gypsum wallboard
  • 450 plf = 840 plf for isolated braced wall panels with gypsum wallboard

This codified math provides a significant competitive advantage for the OSB products of APA members.


Why are these design values used?

Why is this math acceptable to the ICC, building code officials and the engineering community? Perhaps more importantly, why does APA not correct this in the IRC? They have never disputed SBCRI’s testing by providing real-building test data using ASTM E564 techniques (i.e. trusses on top of the walls versus their standard E72 test method that uses a steel beam to rigidly apply lateral loads, etc.). The BCCS report also states that the SBCRI testing provides a reasonable result. The answer might lie in the fact that keeping up the IRC tradition has its benefits.

Mr. BJ Yeh of APA related the following concept in a January 3, 2013 APA/SBCA staff meeting recap documented in a January 24, 2013 SBCA thank you letter:

BJ Yeh articulated, in a very elegant and forthright manner, our industry’s primary concern using the following words to reflect the point of view he expressed, which is a concept we have all heard many times; the prescriptive code is based on historical performance and essentially fundamental engineering does not really “apply” or “work” because structures built using traditional and conventional methods have a good resistance track record.

Mr. Ed Elias, APA's Vice President, also made the following observations in a February 6, 2013 letter from APA in response to SBCA’s January 24, 2013 thank you letter:

1.       The technical information required should support or be used to modify existing code-supported provisions such as established systems or risk factors related to product equivalency. This information would most likely be used to support the introduction of new materials and systems, as opposed to challenging existing products. For example, existing OSB design properties are not the target; but currently recognized systems and product equivalency procedures are.

2.       We (APA) believe that a major goal for the SBCA position is to provide a cost-effective engineering solution to their membership and as such this goal serves the SBCA membership well. However, by establishing standard factors in which product equivalency or system performance are applied generically, an unintended consequence may be that non-wood products (e.g. foam sheathing) gain an advantage and supplant traditional OSB market share. This is not in our Association members' best interests.

3.       Our staff is prepared to critically review and support technically justifiable programs brought forth…...

Following up with APA to set a better performance foundation, SBCA sent a detailed letter on September 23, 2013 regarding the testing and analysis that it had undertaken. In that letter, SBCA summarized the information SBCRI generated to begin the process of setting a good technical foundation:

The purpose of this letter is to be precise as to what the SBC industry is going to set as its engineering foundation/performance benchmarks for wood structural panel (WSP) unit shear wall capacity values and section 104.11 equivalency evaluation. This evaluation is based on all of the testing and findings to date that we have access to. We believe that it is important to be completely transparent in our approach so that APA/AWC can provide engineering mechanics test data/analysis and installation procedures to provide justification for different benchmarks than those provided here, if so desired. As you said in your February letter, “The technical information required should support or be used to modify existing code-supported provisions such as established systems or risk factors related to product equivalency.” This work is clearly in the domain of APA/AWC.

This information has been met with the perspective that SBCRI testing is unsubstantiated and that SBCRI-SBCA analysis with respect to OSB shear design values being overstated is based on non-standard test methods. Also, it has been asserted that universities and other research organizations, the consensus opinion of the code and standard committees, and the extensive performance history of wall assemblies sheathed with OSB sheathing show that the current shear design values provided in the APA publications are valid. Finally, the current shear design values are referenced in the International Building Code (IBC) and the IBC referenced Special Design Provisions for Wind and Seismic standard, so everyone using those documents must know they are correct as they are adopted law.

This is just the beginning of the facts that SBCRI has that should be considered as one evaluates OSB in shear wall applications. SBCA will be sharing this information in the future detailing one engineering consideration at a time to keep the content as concise as possible.

The SBCRI-SBCA goal is to provide a set of facts that have test data behind them, provide all appropriate references and undertake common-sense analysis. From there, and based on the merits, the reader can decide. We appreciate any comments, data and new analysis that will add to our knowledge.

Ultimately SBCRI hopes that this information will lead to action, as appropriate, by building code officials and the engineering community. We know that tradition can become entrenched and can get in the way of thoughtful and valuable building construction advancements. The foregoing information is intended to define the law and also provide a pathway to showing equivalency to the law.


PDF icon 130613_apa_letter_to_sbca.pdf110.34 KB

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