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Self supporting hip roof framing?

Jobsaver

Jobsaver

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Joined
Oct 12, 2010
Messages
851
Location
Central Arkansas (pop. 30,000 - near Little rock)
Some suppliers specifying engineered beams (using beam calculator software) will often attribute a very significant point load on a ceiling beam having a required brace running from a point on the beam to a ridgeboard to hip rafters connection.

I recently acquired a calculation where such a point load was deemed to be 12,000 lbs on a 28' wide garage having a 10/12 pitch roof.

Some claim true rectangular or square hip roof structures are self-supporting.

If hips are self-supporting, why are braces required? To what extent do the opposing forces of a symmetrical hip roof system relieve the point load resulting from a roof brace?

In the above example, the supplier specified a humongous beam that did not appear justified.

I know . . . require engineering. Any other comments?
 
R802.3 &802.3.1 make it easier to design as a simple beam than to show that the loads are "designed to carry and distribute the specific load at that point"
 
DRP said:
R802.3 &802.3.1 make it easier to design as a simple beam than to show that the hips are "designed to carry and distribute the specific load at that point"
Click to expand...
Sorry can't seem to edit, it says I'm missing a security token.
 
This is a question I have all the time also. We are always putting beams under the hips with a king post going to where the hips meet the ridge, per the engineer's requirement. What I don't understand is why is it required now when in years past if I've sen one hip roof I've seen dozens with no beams adding extra support; I've built hip roofs with no beams acting as supports years ago and those structures are still standing with no apparent deflection.

Is this a case of the code getting carried away or is there a valid concern about this situation?
 
A simple hip up to a certain span is usually self-supporting. However, many newer roof designs are no longer simple, but are broken up with cross-gables, etc. coming off in all directions. I-joists & LVL hips are sometimes used to get longer spans than you could with lumber, which is usually limited to 20' lengths around here. Wind uplift requirements have become tougher in current codes. For all these reasons it's easier to design a hip roof using beams and posts with tiedown straps than documenting that it's self-supporting.
 
Paul said it pretty well....too many people I see, don't think anything is ever required at a hip because they don't understand the "system" approach to buildings...they have seen it similar before and try to duplicate. The code is prescriptive...follow it, engineer it, or change it....

I drove 80 on the way in today and noone died...doesn't mean it is right (not legal)...and someone may die someday, just not today...no perceptable ill affects does not make it right, just means we got lucky...
 
Jobsaver said:
Some suppliers specifying engineered beams (using beam calculator software) will often attribute a very significant point load on a ceiling beam having a required brace running from a point on the beam to a ridgeboard to hip rafters connection.I recently acquired a calculation where such a point load was deemed to be 12,000 lbs on a 28' wide garage having a 10/12 pitch roof.

Some claim true rectangular or square hip roof structures are self-supporting.

If hips are self-supporting, why are braces required? To what extent do the opposing forces of a symmetrical hip roof system relieve the point load resulting from a roof brace?

In the above example, the supplier specified a humongous beam that did not appear justified.

I know . . . require engineering. Any other comments?
Click to expand...
This is circular thinking, once you add a "brace" you design the load to be born by that point. Remove that "required brace" and you will no longer have a point load there, the loads will disperse along the other framing members.
 
"...In the above example, the supplier specified a humongous beam that did not appear justified...."

Pricing by board foot, like pricing by the pound, may affect the vendor's choice of how much to sell.

When my wife asked the honey-glaze ham store how much she needed to feed 12, they specified enough to feed 32!
 
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