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RE: Not a Structural Question, but maybe someone on this list can help

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Bill

 

I have often seen and accepted 2x’s as a means of substitution for GWB when for practical reasons it is not feasible to install GWB in the assembly. One classic example is the in floor/wall intersection of 2 hour rated walls. In those cases blocking for the full width of wall is normally accepted in lieu of running the GWB all the way on each face of the wall.

 

In your case you may want to consider the following:

 

1-     As you said you may want to consider the lower ceiling as the roof ceiling rated assembly and since the top side of your assembly in unoccupied space only the lower part needs to be rated (footnote 14 to Table 7-C of UBC in regard to item 21 of the table)

2-     Run two layers of GWB at the bottom of the lower ceiling if CBO is not happy with option 1.

3-     Verify with the architects if you really need a one hour corridor. This is one of those elements of the code that is often misconstrued and required unnecessarily.

 

Good luck

Ben Yousefi, SE, CBO

Santa Monica, CA

 


From: Bill Allen [mailto:T.W.Allen(--nospam--at)cox.net]
Sent: Thursday, June 01, 2006 8:11 AM
To: seaint(--nospam--at)seaint.org
Subject: Not a Structural Question, but maybe someone on this list can help

 

I’m working on a project which is a one story wood framed structure in California. It’s rated as Type V One Hour Sprinklered. There is an interior exit corridor which is a one hour rated corridor. The wall is load bearing and has TJIs hanging off one side and 2Xs hanging off the other side (in the corridor). There is one layer of Type X GWB on each side of the wall. There is no issue at the roof framing as the GWB runs between the roof framing and the contractor will caulk between the roof joist members.

 

This is a detail on the approved plans which the building official has agreed to: http://www.allendesigns.com/projects/20411/Detail23SheetA92.jpg

 

The issue is at a lower ceiling in the corridor. The contractor installed the ledger to the studs and interrupted the GWB. He is willing (and originally intended to) fire caulk the joint between the interrupted GWB and the ledger.

 

Here is a sketch of the proposed change: http://www.allendesigns.com/projects/20411/Detail23SheetA92-Alternate.jpg

 

The building official is unwilling to accept this change without the architect changing their detail. Rightfully so, the architect is unwilling to provide a detail which has not been documented to be acceptable as a one hour rated assembly. However, I believe this condition happens often.

 

The question is this: Does anyone know of a published approved method of interrupting the GWB on a one hour interior wood framed wall?

 

Of course, another option I thought of (although I am no means an expert in fire rated assemblies), is to consider the lower corridor ceiling the bottom of the fire rated ceiling, but I’m not sure if that is possible.

 

TIA,

 

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

ALLEN DESIGNS

Consulting Structural Engineers
 
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