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Re: Gypsum ceiling as structural diaphragm

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Thank you!  I must have flipped through too quickly.
I also found it in the 2003 IBC section 2508, but that sections stops you at 70/90 plf.  Now its time to crunch numbers to hopefully get it to work for 150 plf...
Jim Wilson

AWC Info <AWCInfo(--nospam--at)> wrote:

AF&PA's Wood Frame Construction Manual (WFCM) for One- and Two-Family Dwellings, 2001 Edition outlines a procedure for calculating diaphragm capacity to brace gable endwalls against wind loads. The tabulated gypsum diaphragm capacity is 70plf, with a note that it can be increased to 90 plf when ceiling framing members are spaced 16" o.c., per ICBO Report No. 1874-89.

Table 3.15 of the WFCM actually tabulates minimum attic floor/ceiling lengths for various wind loads and building geometries. WFCM Table 2.6 outlines lateral diaphragm loads that are used in Table 3.15. The WFCM Commentary provides background calculations for all these tabulated values.



John "Buddy" Showalter, P.E.
Director, Technical Media
AF&PA/American Wood Council
1111 19th Street, NW, Suite 800
Washington, DC 20036
P: 202-463-2769
F: 202-463-2791

The American Wood Council (AWC) is the wood products division of the American Forest & Paper Association (AF&PA). AWC develops internationally recognized standards for wood design and construction. Its efforts with building codes and standards, engineering and research, and technology transfer ensure proper application for engineered and traditional wood products.

>The guidance provided herein is not a formal interpretation of any AF&PA standard.  Interpretations of AF&PA standards are only available through a formal process outlined in AF&PA's standards development procedures.


From: Jim Wilson <wilsonengineers(--nospam--at)>
Subject: Gypsum ceiling as structural diaphragm
To: seaint(--nospam--at)

I thought this was discussed a few months ago, but I can't find it in the archives -
Can a ceiling covered with gypsum drywall be used as a structural diaphragm to resist lateral wind loads? If so, what are the loading limits and other assumptions and precautions that go along with it?

This is a single story gabled end wood structure. The out-of-plane load per foot at the base of the end truss is about 150plf. At their peak, the trusses will be 16ft tall (piggy-backed) practically eliminating the possibility of bracing with kickers up to the roof diaphragm.

Jim Wilson, PE
Stroudsburg, PA

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