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Re: RESIDENTIAL: Discussion of Load Paths

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Meaning ABSOLUTELY no disrespect--because these are the kinds of comments that I get from "all sources"--but this is difficult for me to understand. It sounds like more of those "residential roofs aren't amenable to the laws of statics" comments that I seem to hear from many.
 
They do follow the rules of statics, I hope it did not sound as if I was impling that they didn't. I'd be sceptical of anyone who said that residential roofs don't.
 
The two hips don't actually "oppose each other" because they are BEAMS framing into a common point--unlike rafters, for example. If you have two hip beams with a slope of, say between 30 and 45 degrees, coming together at a "point", that common point isn't held up by a sky-hook! It has to be supported somehow,
 
Do a FBD at the hip to hip to ridge connection, You will see that the assumed horiz resisance required by statics is met by the opposing component of the opposing hip and the other component is forced into the ridge board. (From there you could reason the sheathing transfers the inplane load to the sidewall shearwalls) The vertical component is not taken by the sheathing but rather the first set of common rafters (king rafters). These rafters also frame in the roughly the same location as the hips do. This load is never seen by the sheathing.
 
 
 
 UNLESS you can show that the diaphragm action of the sheathing keeps them in place. These are NOT "out of plane" forces I'm talking about, they are IN-PLANE forces of the sheathing that is NOT in the plane that is defined by the two hips (I hope that's clear; personally I always have a problem with verbal descriptions of geometry).
 
Is the hip holding up the sheathing or is the sheathing holding up the hip? I'll bet on the hip. I always like to put a support at the end of the hip as opposed to the king rafters carring it but my point is that it can be done (no vertical support) and the physics support it. It's staying in the air does not mean that the sheathing is holding it up (not to say that the sheathing doesn't somewhat aid in the support but the hip is holding up the sheathing)
 
If so, fine. If not, well, as someone else here said, there are some engineers that insist on columns or struts at those locations
 
HTH,
Rand