Specifying with AWPA Use Categories
The Use Category System was developed and is maintained by the American Wood Protection Association (AWPA). It’s purpose is to provide a simple way of selecting the proper preserved wood product directly related to the appropriate AWPA Standard. The Use Categories define a set of exposures for preserved wood in the environment. Each exposure has a different degree of deterioration hazard.
There are five different Use Categories, based on exposures and product performance. All preserved wood products can be placed in one of the five categories. There are also subcategories within each Use Category reflecting specific conditions and uses. The amount of preservative in the product, or the retention, and depth of penetration of the preservative in the wood are guided by these categories.
The smaller the Use Category number, generally the lesser amount of preservative is required to provide the necessary level of protection from fungal decay or termite attack. Likewise, the highest Use Category number signifies the highest degree of protection to wood used in the most severe service conditions.
Use Categories
Review the following Use Categories describing the exposure conditions the wood may be subject to in service as well as the typical applications:
UC1 and UC2 wood products are used in interior construction, such as studs, joists, roof trusses, furniture and millwork. The chief threat in these two Use Categories is termites and, as such, are typically preserved with borates. For areas where the Formosan termite is present, higher borate retentions are specified.
UC1 products are for dry interior use, while UC2 products are used where there is potential moisture exposure and there is a need for protection against decay fungi as well as termites.
UC1 service conditions: Above ground, interior construction, dry. Protected from weather and interior sources of water such as leaking plumbing, condensate, pools and spas.
UC2 service conditions: Above ground, interior construction, damp.
Typical applications: Interior construction, sill plates.
Products in UC3A may be exposed to the full effects of the weather, but are oriented in vertical exterior walls or other types of construction that allow water to quickly drain from the surface.
Service conditions: Above ground, exterior, protected, coated and rapid water run-off.
Typical applications: Coated millwork, siding and trim.
Materials in UC3B are used where they are exposed to all weather cycles including intermittent wetting, but with sufficient air circulation so wood can readily dry. See UC4A for sawn components that may be physically above ground but that are required to be treated for ground contact. This includes sawn components that are difficult to replace and critical to the structure, or that may be exposed to ground contact type hazards due to climate, artificial or natural processes or construction.
Service conditions: Exterior construction, above ground, uncoated or poor water run-off. Excludes above ground applications with ground contact type hazards.
Typical applications: Decking, railings, joists and beams for decks and freshwater docks, fence pickets, uncoated millwork.
Products treated under UC4A are those used (1) contact with the ground, fresh water, or other situations favorable to deterioration; (2) used above ground but are difficult to maintain, repair or replace and are critical to the performance and safety of the entire system/construction; or (3) used above ground but may end up in ground contact or are subject to hazards comparable to ground contact due to climate, artificial or natural processes or construction.
Service conditions: Ground contact or fresh water contact. Includes above ground applications with ground contact type hazards or that are critical or hard to replace.
Typical applications: Sawn fence, deck and guardrail posts, structural lumber, joists and beams for decks and freshwater docks, timbers.
Wood in the UC4B category is typically used in contact with the ground in severe environments, in climates with high potential for deterioration and in critically important components. Wood treated to UC4C can be used where there is extremely high potential for deterioration, with considerable exposure to moisture such as in rivers or lakes.
UC4B service conditions: Ground contact or fresh water contact, heavy duty, critically important components.
UC4C service conditions: Ground contact or fresh water contact, extreme duty, extremely critical components.
Typical UC4B applications: Permanent wood foundations, building poles, horticulture posts, utility poles, decking, above tidal piers and docks, and in areas with high potential for fungal decay.
Typical UC4C applications: Land or fresh water pilings, foundation pilings and utility poles in areas with a severe potential for fungal decay.
Wood treated to UC5 is preserved for the most demanding conditions such as salt water immersion where it may be exposed to marine borers and other salt water organisms. Unlike the other Use Categories, the subcategories are based on the location where the product will be used, reflecting the specific threats posed.
Wood treated to UC5A is intended for use north of San Francisco on the west coast and New Jersey on the east coast. UC5B is intended for wood used south of San Francisco on the west coast and New Jersey on the east coast. UC5C is set for use on the Gulf Coast and south of Georgia, as well as Hawaii and Puerto Rico.
Service conditions: Salt and brackish water and adjacent mud zones; continuous marine salt water exposure.
Typical applications: Marine pilings, bulkheads, bracing.