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Re: Roof Sheathing at Ridges

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And now for my $0.02 worth.

In a high wind area, there are roof "diaphragm" shear forces parallel to
the ridge, resulting from transfer of sheathing to framing shear forces
from roof sheathing fasteners.  I say "diaphragm" because it is not
common to perform a structural diaphragm analysis for residential roof
or floor construction.

In a common (e.g. flat) diaphragm, the sheathing edge joints can be
unblocked or blocked, depending on the magnitude of the diaphragm shear
forces. Typically, the framing is continuous at the unblocked sheathing
edge. However, at the ridge of a pitched roof, the framing has a joint
which is fastened by a metal plate (if trussed roof), or simply
toenailed if the roof has a ridge beam or ridge board.  The joint in the
framing at the ridge, and the discontinuity of the roof sheathing with
an unblocked edge, create a weakness at this location, in resisting
forces parallel to the ridge. Therefore, some reinforcement along the
ridge may be required in high wind regions, to transfer "diaphragm"
shear forces across the ridge from one side of the roof to the other.  A
suitable detail for placing intermittent blocking between roof framing
and attaching roof sheathing to the blocking, is shown in an APA
publication on construction for high wind regions (for a copy, contact
APA Help Desk at help(--nospam--at)apawood.org).  This detail may also be required in
some high seismic regions, depending on the roof configuration and
resulting forces.

So Thor Tandy is on the right track - some special construction upgrades
may be required in this application.  And, you are to be commended for
raising a question about this construction detail.

John Rose
APA (Retired), Tacoma, WA

"M. David Finley, P.E." wrote:

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