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Roof Load Duration "CD" & Members Below

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Yes. NDS® Section states that, "The load duration factor for the shortest duration load in a combination of loads shall apply for that load combination." NDS Appendix B provides some additional discussion as does the NDS Commentary Chapter 2 at

Hope this information helps.

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: Joseph Harouni <jharouni(--nospam--at)>

Subject: Roof Load Duration "CD" & Members Below

To: <seaint(--nospam--at)>



I would like to know if one can use the 1.25 Roof Load Duration "CD"

stress increase for members at stories below roof level, where these

members besides carrying the roof load are also carrying live load of

floors below (Sec. T 2.3.2, 2001 CBC, 1997 UBC, 2002 L.A.B.C.)


Joseph Harouni