All building codes require that
walls be braced to resist racking
caused by wind loads (see illustration
below.) Most prescriptive codes
recommend one of three options:
1x4 diagonal bracing, 5/8-inch diagonal
board sheathing, or 3/8-inch
plywood sheathing. Other more
progressive performance-based codes
specify minimum design values for
racking resistance, but let you
achieve them with almost any
materials you choose. For example,
you can count the combined contributions
of metal strapping, drywall,
interior partitions, and ceiling
diaphragms.
Some foam sheathing manufacturers
point to these performancebased
measures as proof that a
foam-sheathed wall meets code. It's
true that with the right floor plan,
wall dimensions, and number of
wall openings, an unsheathed or
foam-sheathed wall might comply
with code. But bear in mind that
most code officials