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RE: Full height stud requirements in IRC2000/2003

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I think they used to have a rule in CABO the predecessor to the IRC that said
you needed to have half the number of interupted studs on each side of the
opening. The Anchorage building  department used to have a handout requiring
this also. 

The IRC table with heights greater than 10 feet has a footnote that limits
tributary width to the wall of 6 feet, 25 psf snow and 100 mph wind.

In alaska they always use R19 insulation so they have 2x6 @ 16" studs and
they normally calc out by themselves for a 10' wall even with the snow loads
and high wind - single king jambs don't normally calc out. 

-----Original Message-----
From: Jordan Truesdell, PE [mailto:seaint1(--nospam--at)truesdellengineering.com] 
Sent: Tuesday, June 27, 2006 9:26 AM
To: seaint(--nospam--at)seaint.org
Subject: Full height stud requirements in IRC2000/2003

Does anyone know if there are any requirements for the number of full height
(aka "king") studs in residential construction in the IRC (2000 or 2003)?  I
just ran across an installation with a 16' wide rollup door in a 10' tall 2x4
stud wall, with double jack and single(!) king studs.  
I'd like to reference an IRC provision that prohibits such an assembly, but
it appears from my reading that there is no requirement that a jamb must have
more than a single full height stud, regardless of opening size.  The WFCM
has a check for king studs, and a quick glance at one example showed that the
number required appeared to be in line with what I'd expect from bare calcs,
but there doesn't seem to be any mention of this in the IRC. Am I missing
some obscure provision that's not in the wall or floor sections? The floor
section lists header sizes with the number of jack studs necessary, but no
mention of the king studs required.

On a side note, is anyone aware of some testing which was done to come up
with the allowable stud heights in the IRC? The data they have does not match
the NDS requirements, and I'm curious whether the tables were developed by
engineers, some destructive testing research, or the NAHB lobby. Checking the
walls using the table R602.3(5), supporting roof and ceiling only, 10' tall
SPF studs @ 24" o/c, I get a deflection of L/96 and an Es3.9-3 combined
stress index of 1.81 with a 24' rood truss and 17.8psf wind (90mph gust, zone
4, exposure C, 33.3SF EWA - well within 
the applicability of the IRC).    At 24" o/c, the 1.5/1.15 increase in 
strength allowed in  the IBC 2306.2.1 doesn't apply, and even if it did, the
combined stress would be still be >1, and there is no acceptable criteria for
wood walls which is less than L/120 in section 1604.3 of the IBC.

--
Jordan


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