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Q.I recently inspected a home that had 3/8-inch OSB corner bracing. The surface stamp indicated that the strength axis of the panel ran in the long direction (see photo, below). I assume this means the panel should be applied with the long dimension across the studs, yet the builder had installed the long dimension parallel to studs. I called APA to check and was told the stamp only applies for roof sheathing and not to corner bracing. Why is the strength axis important for roof sheathing but not for corner bracing?

A. Scott McVicker, a structural engineer in Palo Alto, Calif., responds: There are two properties of OSB panels at play here: its strength in shear and its bending strength. When using OSB for corner bracing, shear strength — the ability of the panel to resist lateral racking movement — is the issue, and the panel’s shear strength is not affected by its orientation. But place that same sheet up on the roof across rafters 24 inches on-center and stand in the middle of the span between two rafters: Now the bending strength of the panel is at play. That’s what the arrows refer to.

If you look carefully at the sheet of OSB in question, you’ll see that most of the fibers are oriented parallel with the length of the sheet, making that the strongest axis in bending.

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