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Re: Conventional Wood Framing

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Small homes can be done more-or-less prescriptively.  I believe the IRC discusses it.
But when I design high-end homes, I use the traditional engineering approach.  Rafters supported by perlins, braced by struts.  Struts are anchored to wall top plates.  Joists in tension contain the outside walls.  There are publications that prescriptively do some of that, but it's same as any other design.

>>> "Jordan Truesdell, PE" <seaint1(--nospam--at)> 8/28/2007 10:35 AM >>>
No, they are supported by magic.  Okay, not really magic, but a careful random combination of gwb ceiling tension, unanticipated load paths through non-loadbearing walls, and hoop stresses in the roof diaphragm.  The IBC, if I remember, is no more helpful than what you've probably found in the UBC.

If you do a diligent trace of the loads, you'll find that certain, simple geometries will work without support, but that most modern plan-book and architect-designed roofs do not work by normal mechanics. Sometimes you can get a hip end to work by making a multi-ply king post truss at the end.  Many valleys and hips use the same principal as ridgeboards, but few non-engineers make sure that all the forces resolve somewhere definable.

I believe the building codes are written to carefully avoid talking about such things, in hopes that nobody will notice (isolated/spread footings are given similar treatment in the prescriptive design code).

Bill Allen wrote:

In conventional wood framing, are vertical members required to support hips, valleys and ridges?


Are there any better references which are more definitive than the single paragraph I’ve found in the UBC?




T. William (Bill) Allen, S.E.


Consulting Structural Engineers
V (949) 248-8588 F(949) 209-2509

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