The APA's recent proposal (RB164) to expand the use of the narrow wall bracing method was defeated at the International Code Council's Final Action Hearings held in Detroit, September 28 - October 2, 2005. Several industry leaders, including Simpson Strong-Tie, presented compelling test evidence that impacted the outcome of the vote.

In the 2004 Supplement to the International Residential Code (IRC), narrow braced walls are permitted in limited applications. In 2005, the APA attempted to expand this application to include higher seismic zones, second-story applications and usage away from corners. However, test results completed by Simpson and Washington State University (WSU) indicated there were significant performance issues that need to be addressed.

Test Results Completed by Simpson Strong-Tie and Washington State University

Prior to the ICC Final Action Hearings, Simpson initiated a comprehensive testing program to understand the performance of narrow wall systems and see if the APA test results could be replicated. There were a number of concerns with the proposed code change. The testing focused on three main issues:

• The Use of Gypsum
  Although the use of gypsum is required by the code, APA's in-house tests did not include gypsum. The Simpson testing used gypsum on the interior of the APA narrow wall and compared it to a standard, code-accepted benchmark wall. Simpson’s testing indicated that the APA wall performed approximately 20% below the benchmark wall when both walls were constructed per code.
• Common Installation Errors
  In APA's test report covering common installation errors, the tested walls used a 15,000 lb. ultimate capacity holdown. This holdown is not listed as a requirement in APA's specifications. Therefore, Simpson completed testing without the use of this holdown device to simulate the condition where no uplift restraint is provided by the return wall because of wind loads acting on the return wall. Common installation errors, such as missing nails were tested, which decreased the wall's performance dramatically. Changing the nail spacing from 3" on center to 4" on center, for example, resulted in an approximate 50% reduction in performance.
• Load Capacity
  After repeated testing and modifications to test set-ups to address issues such as load beam stiffness and holdown bolt tension, Simpson was unable to replicate the loads published by the APA. Although variations in results are expected in this type of testing, Simpson consistently achieved load capacities well below those stated by the APA. It was then that Simpson asked WSU to perform a similar independent research and testing program.

WSU tested the narrow walls and code-accepted benchmark walls. At design levels, the WSU testing indicated:

• The narrow walls performed significantly below the code accepted benchmark walls (36% below).
• The WSU test results of the narrow wall performance were 36% to 54% below APA's results.

ICC Hearings and Next Steps

Simpson and WSU test results were presented at the ICC Hearings this fall. The proposal to expand the use of the narrow wall bracing method, RB164 was voted down and denied approval.

In an effort to clarify the bracing provisions outlined in the IRC, a task group of industry leaders has been assembled and will meet in January 2006. The goals of the task group include:

• Re-organizing and simplifying the wall bracing provisions of the code (a non-technical rewrite);
• Developing additional standards for testing and evaluating existing and new bracing methods;
• Researching the effects of combining various wall bracing systems;

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