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RE: Hip Roof Questions (conventional wood framing)

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Don,
 
I recall a post in the past year or so from one of our resident authorities in wood construction that hips that are less in plan than 12'x12' have typically performed well without any interior posting or "beam" members.  I could be mis-quoting the intent of that post and I don't have the specific wording on hand.
 
If a roof is tied in both directions, I do not design the hip rafters as structural.  Where the rafters are precluded from spreading at the base, there is little vertical force exerted on the hip, and therefore the "beam" becomes a waste of money.  The steeper the roof pitch, the more comfortable I am with this assumption.
 
Personally, I refrain from using true valley rafters at all in major roof construction.  Too much concern for rafters to pull apart.  Instead, I have successfully convinced builders to overframe these conditions.  Overframing also permits full installation of the ceiling joist/rafter ties, and subsquently reduces the need to design beams and interior posts.  I have seen a few true valley's in relatively flat and very small roofs, such as exposed porch roofs.  Designing those as beams has worked fine.
 
Intersecting hips seem to be the biggest problem with these elaborate homes being built today.  Overframing becomes impractical and posting becomes essential.
 
The IRC vaguely requires ties to be installed in both directions in hip roofs.  The lesser direction only requires ties at 4' on center, but makes no mention of how to handle the heal/joint connection.  IRC 2006 has improved upon this language to require collar ties in addition to rafter ties in both directions.  I don't believe the posting language has changed from what Dave quoted.
 
Jim Wilson, PE
Stroudsburg, PA

Dave Adams <davea(--nospam--at)laneengineers.com> wrote:
Don,

I don't know if your particular application is residential, but Section
R802.3 of the 2003 International Residential Code (conventional
construction) requires a brace, post or equivalent to support hip and
valley rafters near their point of attachment at the ridge, otherwise
they must be "... Designed to carry and distribute the specific load at
that point." Intentionally somewhat vague, I think, to allow for a
variety of engineered alternatives to justify the omission of a post or
brace.

Dave K. Adams, S.E.
Lane Engineers, Inc.
Tulare, CA
E-mail: davea(--nospam--at)laneengineers.com





-----Original Message-----
From: Donald R. Bryant, PE [mailto:dbryant61(--nospam--at)cox.net]
Sent: Tuesday, May 09, 2006 9:14 AM
To: seaint(--nospam--at)seaint.org
Subject: Hip Roof Questions (conventional wood framing)


Dear Listers,

I am in a quandry, and have been here for some time. I have seen many
hip roofs, even some with a valley intersecting where the hip hits the
ridge, constructed without a post.

I normally calculate all hips as beams and all valleys as beams (the
procedue I uses shows that a valley beam receives twice the load of a
hip). I always design a post to support the end reaction of the hip
and/or valley beam.

This is long-winded, but I am getting to it. Could someone please tell
me, based on the code, when it is OK not to support a hip, or a valley,
with a post? A parallel question is: when is a hip a hip board, and not
a hip beam?

Thanks,

Don



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