- 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.