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To perform reliably in service, wood commodities must be pressure-treated to designated standards of preservative penetration and retention necessary to endure the expected decay hazard. Penetration refers to the depth a preservative must permeate into the wood fiber during the pressure-treating process. Retention levels refer to the amount of preservative that remains in the wood after the pressure-treating process is complete. Retentions are expressed in pounds of preservative per cubic foot of wood fiber; the higher the number, the harsher the condition to which the wood may be exposed.

The American Wood Protection Association Use Category (UC) System under Standard U-1 specifies categories of exposure that wood commodities typically encounter in service. The UCS helps users identify the exposure condition for specific products and end-use environments, and then specify the acceptable preservatives and retention levels necessary for that application. Specifiers should become familiar with the Service Conditions for Use Category Designations (Table 3). Commodity Specifications (Table 4) designate the general classification of treated wood commodities.

Approved preservatives and retentions for treated Southern Pine by end-use, application and exposure condition are summarized by Commodity Specification (Tables 5-10). When purchasing under the Use Category System, material orders should include the Use Category designation (Table 3), general Commodity Specification (Table 4), and specific enduse and preservative and retention level (Tables 5-10). Any special requirements such as pre- or post-treatment preparations (including conditioning and drying) should also be indicated. See specification example below.

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NOTE: Table 3 copyright AWPA, Book of Standards, 2008 Edition, Section 2, Service Conditions for Use Category Designations.

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