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Wood supporting masonry or concrete - UBC 2307

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Title: Wood supporting masonry or concrete - UBC 2307


I'm not sure of the origin of the 4" limit in the UBC, however, we recently updated this provision in the IBC. Note, there's a requirement to check wood members for long-term loading (creep) per NDS(r) 3.5.2 if the slab exceeds 4" thickness. Here's a link to an article that appeared in Structure Magazine recently that provides a little more background:



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: "Jeff Smith" <JeffSmith7(--nospam--at)>
To: <seaint(--nospam--at)>
Subject: Wood supporting masonry or concrete - UBC 2307

I have been asked to put a 10' x 10' X 6" concrete slab on new wood framing to dampen a piece of equipment. The floor framing will be heavy PSL's w/ 1-1/8" ply. Section 2307 limits the concrete to 4". Does it seem reasonable to design the wood framing to support this 6" slab and equipment. What is is the ori=gin of the 4" limit to concret on wood?

Thank you,
Jeff Smith