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RE: RESIDENTIAL: Discussion of Load Paths

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Bill,

There are a number of ways to deal with this – depending on the type of ceiling below.

  1. The rafters off the hip that run parallel to the ceiling joists can still be tied at the plate to form a modified Carpenters truss to omit the thrust at the plate. This is pretty common. The rafters parallel to the ridgeboard don’t need to be tied as the ceiling joists will have prevented these rafters from placing outward pressure on the sloped hip end framing. Please make sure that you use a decent Hip/Ridge connector (or a simple connector when the point of connection is at another carpenter truss and ridgeboard) – Simpson makes a number of these
  2. If manufactured trusses are provided, the actual hip is usually eliminated. Instead, a series of trusses reducing in height (seen as a cross section of the sloping end of the roof) makes up the hip end, and what would appear to be the hip beam is actually the top chord of the truss and left extended so that the roof is closed in from above by conventional lumber. If you need to see this in more detail, I think I can find a detail from a truss package (truss elevation) that I can send to you. It seems a little unusual when you look at it, but almost every roof I’ve done with a hip end (not a Gable) is manufactured in this manner that supports the wall similar to number 1 above by using the bottom chord of the truss to act like a ceiling joist or rafter tie.

 

Hope this helps you,

Regards

Dennis

 

Dennis S. Wish, PE

California Professional Engineer

Structural Engineering Consultant

dennis.wish(--nospam--at)verizon.net

http://www.structuralist.net

 

-----Original Message-----
From: Bill Polhemus [mailto:bill(--nospam--at)polhemus.cc]
Sent: Friday, October 08, 2004 8:02 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: RESIDENTIAL: Discussion of Load Paths

 

Good comments, however...

 

Note the quote below:

 

"...many time[s] two hips oppose each other and a ridge frames in at the same point you could resolve the forces into a self supporting system up to a critical load which would be much lower than the critical load if you put a support at the end of the hip or valley. But again the diaph has very little to do with this."

 

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.

 

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, 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).

 

If so, fine. If not, well, as someone else here said, there are some engineers that insist on columns or struts at those locations.


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