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FW: Ceiling joists/rafter ties IRC R802.3.1

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From: AWC Info <AWCInfo(--nospam--at)afandpa.org>
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FROM BUDDY SHOWALTER, PE WROTE:

If it is a hip-beam system, there is no thrust... So it only needs to be
tied together to resist out-of-plane wind loads... Analogous to a ridge beam
system.

If it is a hip rafter system (conventional construction), it needs to be
tied together in both directions because the hip rafter is just a connection
point... Analogous to a ridge board system.

HTH

Buddy

John "Buddy" Showalter, P.E. Director, Technical Media AF&PA/American Wood Council 1111 19th Street, NW, Suite 800 Washington, DC 20036 P: 202-463-2769 F: 202-463-2791 http://www.awc.org
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Buddy,
This is an interesting discussion for a number of reasons. In my area stick framing is rare - the hip roof construction is generally left to plated trusses. Where the hips start to decend to the end wall (sloped) the truss company will supply a series of rectangular trusses that reduce proportional to the slope of the roof and are parallel to the end walls - this eliminates the need for hips unless the trusses are intended to saddle into a triangular hip truss at each side.
Conventional construction would still use the idea of having the ceiling joists used as rafter ties. What is interesting here is that I would think the "Carpenter Truss" idea at the end of the building where the hips decend would essentially created a massive ridge system that would not only carry the hips and the outward sloped rafters, but the ceiling joists still running parallel to the end walls will begin to act in compression as the hips and rafters try to thrust the end wall outward. The effect would be similar to pushing out the end wall by pulling in the two corner walls perpendicular to the end wall. The rafter ties would now become compression members.

What I don't see is how you can tie the roof in two directions unless you had some point to tie to. I can understand running a rafter pependicular to the hipped wall on top of the existing parallel ceiling rafters (I've seen this designed), but then you would be subjecting the ceiling rafters to both torsion and bending. The other way might be to create a subdiaphragm connection by blocking at the ceiling rafters and strapping - however, I don't think this is even considered in Conventional Construction.

What is the best way to stick frame a hip end roof?
Best Regards,
Dennis S. Wish ,PE
California professional Engineer
Structural Engineering Consultant



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