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Wet service factor for preservative treated floor joists

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Title: Wet service factor for preservative treated floor joists

Here's a link to an FAQ on the subject:

And, here's an excerpt from the 2005 NDS Commentary:

C4.1.4 ...Applications in which the structural members are
regularly exposed directly to rain and other sources of
moisture are typically considered wet conditions of service.
Members that are protected from the weather by roofs or
other means but are occasionally subjected to wind blown
moisture are generally considered dry (moisture content
19 percent or less) applications. The designer has final
responsibility for determining the appropriate moisture
content basis for the design.

Here's a link to the Commentary if you'd like to download it:



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: "Christopher Banbury" <cbanbury(--nospam--at)>
To: <seaint(--nospam--at)>

Where can I find guidance on the appropriate use of the wet service factor with No.2 southern pine wood floor joists that have been pressure treated?

The raised floor will be part of an under-roof open pavilion. What might I expect the in-service moisture content to be for PT lumber in this condition?

I am reading a 1994 study by Winandy of the USDA Forest Service that seems to suggest that the use of Cm with treated wood may be overly conservative in some cases.


Christopher Banbury, PE

Ark Engineering, Inc.
PO Box 10129, Brooksville, FL 34603
22 North Broad ST, Brooksville, FL 34601
Phone: (352) 754-2424
Fax: (352) 754-2412