Study Finds Flexible Structural Sheathing Under-designed, Unsafe and Unreliable

  A new report finds that manufacturers of flexible structural sheathing overstate their lateral load resistance values by as much as 42 percent. In a study by three independent laboratories—Clemson University, University of Oklahoma and APA – The Engineered Wood Association—five flexible structural sheathing materials available in the marketplace were tested for their wind and seismic lateral load (shear wall) performance. APA published the results in a new Product Advisory: Performance of Flexible Structural Sheathing.
  The evaluations were based on two shear wall test standards listed in each manufacturer’s product evaluation report: ASTM E564, Standard Practice for Static Load Test for Shear Resistance of Framed Walls for Buildings, and ASTM E2126, Standard Test Methods for Cyclic (Reversed) Load Test for Shear Resistance of Vertical Elements of the Lateral Force Resisting Systems for Buildings, Method C (CUREe).
  “Design values published by each product manufacturer are in place to provide safety and reliability to building designs,” said Dr. BJ Yeh, P.E., APA Director of Technical Services. “Therefore, the designers, building officials and consumers are expecting product performance to comply with the published design values.”
  The Product Advisory: Performance of Flexible Structural Sheathing is available for download on APA’s website at
  Detailed test reports are available to building officials and design engineers from APA upon request to


  About APA – The Engineered Wood Association
  Founded in 1933 and based in Tacoma, Washington, APA represents approximately 172 plywood, oriented strand board, glulam timber, wood I-joist, Rim Board and structural composite lumber mills throughout North America. Its primary functions are quality auditing and testing, applied research, and market support and development.
  To learn more, visit

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