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FW: Hip Roof Diaphragm answer from SEAOC

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Mr. Sherman:

AF&PA and APA are a good source for basic wood diaphragm design.  AF&PA?s
help desk telephone number is 202/463-4713 and APA?s telephone number is

These two groups provide the best industry information on diaphragm design
and this design is independant of the structural wood member being used to
support the diaphram.

Special considerations when trusses are the structural support system
include:  Any trusses that are to be used as drag struts should be clearly
indicated on the structural framing plan.  Please be sure to provide the
magnitude of the forces, the means by which they are to be applied to the
truss and transferred from the truss to the shearwalls.  Also, if the roof
sheathing at the hip ends breaks above the joint between the end jacks and
the supporting girder truss, the lateral forces to be resisted by the end
jacks should be specified so that an appropriate connection can be provided
to resist these forces.

I hope this helps.  Please let me know if we can be of any further
assistance in this matter.

Jim Vogt, P.E.
Technical Services

-----Original Message-----

From: Bill Sherman [mailto:SHERMANWC(--nospam--at)]

Sent: Wednesday, August 19, 1998 7:47 AM

To: seaint(--nospam--at)

Subject: Wood hip roof diaphragm

A co-worker of mine is designing a building with a hip roof, using wood

trusses and a plywood diaphragm, and with vents at the ridge line. We don't

do a lot of wood design here and would like some information on limitations


such a design. How do you determine the diaphragm capacity of such a hip

roof? Are there limits on roof slope vs diaphragm capacity? How do you

handle ridge vents relative to diaphragm shear connections?

Thanks in advance for any assistance.