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Standards of the American Wood-Preservers' Association

• Use Category System
• Excerpts from the AWPA glossary
• Specification Guide for Treated Wood End Uses
• Precautionary notes from C2
• Standard M4 Care of Preservative-Treated Wood Products

Standards of the wood preservation industry are established by the American Wood-Preservers' Association (AWPA), an international, nonprofit, technical society founded in 1904 to provide a common forum for the exchange of technical information between industry, research, and users of treated wood.

The Use Category System  

The Use Category System provides a simple way of using the standards of the American Wood-Preservers' Association. The system was proposed in 1999, and defines various exposures for treated wood products. Each exposure has a different degree of biodegradation hazard and/or product service life expectation. The system helps specifiers and product users to locate the appropriate AWPA Standards, which provide recommendations for a specific combination of product and use environment.

The advantage of the Use Category System is simplicity. All treated wood commodities can be placed into one of the use categories. These categories are summarized below in the Use Category Selection Guide.

The system consists of seven categories, based on exposures and expected product performance, ranging from weather protected to salt water marine and fire retardant applications.

In general, as the Use Category number rises, there is a corresponding increase in the required preservative retention. The depth of penetration may also increase. The dimensions of the treated product may also influence the penetration requirement.

USE CATEGORY SELECTION GUIDE
USE CATEGORY	SERVICE CONDITIONS	USE ENVIRONMENT	COMMON AGENTS OF DETERIORATION	TYPICAL APPLICATIONS
UCI	Interior Construction, Dry, above ground	Continuously protected from weather or other sources of moisture	Insects only	Interior construction and furnishings
UC2	Interior Construction, Damp, above ground	Protected from weather, but subject to sources of moisture	Decay fungi and insects	Interior construction
UC3A	Exterior construction, coated, above ground	Coated. Exposed to all weather cycles. Rapid water run off.	Decay fungi and insects	Coated millwork.
UC3B	Exterior construction, above ground	Exposed to all weather cycles and prolonged wetting.	Decay fungi and insects	Decking, deck joists, railings, fence pickets, sill plates.
UC4A	Ground contact or fresh water	For normal ground or fresh water contact. Exposed to all weather cycles.	Decay fungi and insects	Privacy fence posts. Structural lumber & timbers. Guardrail posts. Utility poles in regions of low decay potential.
UC4B	Ground or fresh water contact or important construction components	Severe ground contact or salt water splash. Difficult replacement. Exposed to all weather cycles.	Decay fungi and insects with increased potential for biodeterioration	Permanent Wood Foundations. Utility poles in regions of moderate to severe potential for decay or economic loss. Building poles. Horticultural posts.
UC4C	Ground or fresh water contact or critical structural components	Very severe ground contact. Exposed to all weather cycles. Critical structural components.	Decay fungi and insects with high potential for biodeterioration	Land or fresh water piling. Foundation piling. Utility poles with a severe potential for decay.
UC5A	Salt or brackish water and adjacent mud zone	Continuous marine (salt water) exposure	Salt water organisms. Limornia quadripunctata	Piling. Bulkheads. Bracing.
UC5B	Salt or brackish water and adjacent mud zone	Continuous marine (salt water) exposure	Salt water organisms. Limornia tripunctata	Piling. Bulkheads. Bracing.
UC5C	Salt or brackish water and adjacent mud zone	Continuous marine (salt water) exposure	Salt water organisms. Martesia, Sphaeroma	Piling. Bulkheads. Bracing.
UCFA	Fire protection as required by codes. Above ground interior construction	Continuously protected from weather or other sources of moisture	Fire	Interior roof sheathing. Roof trusses. Studs. Joists. Paneling.
UCFB	Fire protection as required by codes. Above ground exterior construction	Wetting	Fire	Vertical exterior walls. Inclined roof surfaces or other types of construction which allow water to quickly drain from surface.

Excerpts from the American Wood-Preservers' Association Standard M5-03

Glossary of terms used in wood preservation

Incising - the operation of puncturing the lateral surfaces of wood as an aid in securing deeper and more uniform penetration of preservative. (see also - C2 - precautionary notes d & e.)

Penetration - the depth to which preservative enters the wood.

Refusal point - point beyond which the rate of absorption at maximum permitted pressure and temperature is too slow to be significant or does not exceed a specified percentage of the amount already injected when the wood is subjected to refusal treatment.

Refusal treatment - treatment of wood under specified conditions until quantity of preservatives absorbed in a given time is not more than a prescribed percentage of the amount already injected. Treatment to refusal does not however, constitute an acceptable alternative to the minimum penetration and/or retention requirements specified under results of treatment except as specifically listed. This applies to Standard C6 and for oaks in Standard C2.

Retention by assay - the determination of preservative retention in a specified zone of treated wood by extraction or analysis of specified samples such as (a) increment borer cores or (b) chips obtained with a wood bit. The principle applies to freshly treated and to old treated material, and to larger samples if necessary

Specification Guide for Treated Wood End Uses
		AWPA Standards		Preservative Retention Lbs. per cubic foot
		U1	C
		UCS	Commodity	ACZA	CA -B	CCA	Sillbor (DOT)
AGRICULTURE, FARM USE	Round poles and posts as structural members	4B	C4, C5, C16	0.60	0.31	.60	NA
	Sawn poles and posts as structural members	4B	C2, C16	0.60	0.31	.60	NA
	Posts, Fence:
	Round, half & quarter round	4A	C5, C16	0.40	0.21	0.40	NA
	Sawn four sides	4A	C2, C16	0.40	0.21	NA	NA
	Lumber, in soil contact	4A	C2, C16	0.40	0.21	NA	NA
	Lumber, not in soil contact	3B	C2, C16	0.25	0.10	NA	0.25 Hawaii - .42
	Plywood, in soil contact	4A	C9, C16	0.40	0.21	0.40	NA
	Plywood, not in soil contact	3B	C9, C16	0.25	0.10	0.25	0.25 Hawaii - .42
	Grape stakes, sawn	4A	C2, C16	0.40	0.21	NA	NA
BUILDING CONSTRUCTION MATERIAL	Floor plate	2	C2, C15	0.25	.10	NA	NA
	Flooring, residential
	Damp environment	2	C2	.25	.10	NA	NA
	Dry environment	1	C2	.25	.10	NA	0.25 Hawaii - .42
	Framing, interior	1, 2	C2, C15	.25	.10	NA	0.25 Hawaii - .42
	Lumber & Timbers:
	Interior, above ground	1, 2	C2, C15	.25	.10	NA	0.25 Hawaii - .42
	Exterior, above ground	3B	C2, C15	.25	.10	NA	NA
	Ground contact and fresh water use	4A	C2	.40	.21	NA	NA
	Permanent Wood Foundation:
	Lumber & Plywood	4B	C22	.60	.31	.60	NA
	Plywood:
	Sub-floor, damp above ground	2	C9, C15	.25	.10	.25	0.25 Hawaii - .42
	Exterior, above ground	3B	C9, C15	.25	.10	.25	NA
	Ground contact and fresh water use	4A	C9	.40	.21	.40	NA
	Poles, building:
	Round	4B	C4, C23	.60	.31	.60	NA
	Sawn	4B	C2, C15, C24	.60	.31	.60	NA
DECKS	Above ground: Decking, joists, rails, steps	3B	C2, C15	.25	.10	NA	NA
	Sapwood species: Decking, specialties		NER-669	--	.08	--	NA
	Ground contact: Posts	4A	C2, C15	.40	.21	NA	NA
FENCES	Pickets, slats, trim	3A, 3B	C2, C15	.25	.10	NA	NA
	Posts, sawn	4A	C2, C15	.40	.21	NA	NA
HIGHWAY MATERIAL	Lumber and timbers for bridges, structural members, decking, cribbing, & culverts	4B	C2, C14	.60	.31	.60	NA
	Structural lumber & timbers:
	Posts: Round, half-round, quarter round	4A	C5, C14	.40	.21	.40	NA
	Posts: Sawn	4A	C2, C14	.40	.21	.40	NA
	Handrails and guardrails	3B	C2, C14	.25	.10	.25	NA
	Posts, guardrail:
	Round	4A	C5, C14	.50	.25	.50	NA
	Sawn	4A	C2, C14	.50	.25	.50	NA
· Not Approved for CCA-treated wood produced after December 30, 2003. · Not Approved for Sillbor (DOT) – Borate treated wood.

Download this table in pdf format, Specification Guide for Treated Wood End Uses

Excerpts from the American Wood-Preservers' Association Standard C2

Precautionary notes

Note d:

Incising is required of species that are difficult to treat as an aid in securing more uniform penetration of preservative. Incising is required on all faces except for lumber with patterned edges

Where incising is required for wide faces only except for lumber 1" thickness or less. Assumptions must not be made that because a species is listed in this standard or related commodity standards for sawn products and is incised that the species when treated will automatically meet preservative penetration and retention requirements of the standard.

Note e:

Coastal douglas-fir, from a few geographical areas, has been found suitable for treatment with acc or cca. But, it is generally recognized that most sawn products from coastal douglas-fir are extremely difficult to treat with the preservatives acc and cca to the penetration and retention requirements of this standard and related commodity standards for sawn products, even when incised.

Excerpts from the AWPA Standard M4-02

Standard for the Care of Preservative-Treated Wood Products

5. FIELD FABRICATION

   5.1 GENERAL - Whenever practical, all adzing, boring, chamfering, framing, gaining, incising, surfacing, or trimming shall be done prior to treatment. When fabrication after treatment is necessary, the treated wood products shall be treated as described in Section 6.

   5.2 LUMBER AND TIMBERS - When lumber or timbers are used as columns, the end in ground contact shall be an original untrimmed end or shall be field treated in accordance with Section 6.2 regardless of species or thickness.

6. FIELD TREATMENT

   6. 1 Field treatment preservatives shall be applied in accordance with the product label. The application method shall coat any surface that is exposed by damage or field fabrication while not using excess preservative. Any excess preservative not absorbed by the wood product shall be cleaned from the surface prior to the use of the product.
   
   Bored holes for connectors or bolts may be treated by pumping coal-tar roofing cement meeting ASTM-D4022 into holes using a grease gun or similar device.
   
   Careful attention should be given to materials placed into aquatic environments. These materials shall not be used unless the field treated surface is clean, dry and free of excess preservative.
   

   6.2 Lumber and timbers – Lumber and timbers with a nominal thickness of 150 mm
   (6 inches) or less which are used in above ground applications and are of a sapwood species such as southern, red or ponderosa pine, generally do not require field treatment to provide a good service life. When lumber is from a heartwood species such as hem-fir, larch or Douglas-fir, it should be field treated in accordance with Section 6.1.
   

7. PRESERVATIVES

   7.1 General – The appropriateness of the preservative system for field treatment shall be determined by the type of preservative originally used to protect the product and the availability of a field treatment preservative. Because many preservative systems are not packaged and labeled for use by the general public, a system different from the original treatment may need to be utilized for the field treatment. Users shall carefully read and follow the instructions and precautions listed on the product label when using these materials. The preservatives designated in section 7.1.1, 7.1.2 and 7.1.3 are accepted and available for field treatment.
   
   7.1.1 Copper naphthenate – Copper naphthenate preservatives containing a minimum of 2.0% copper metal is appropriate for material originally treated with copper naphthenate, pentachlorophenol, creosote, creosote solutions or waterborne preservatives.
   
   7.1.3 Inorganic boron – Inorganic boron preservatives are limited to use in applications not in contact with the ground and continuously protected from liquid water. They may be used for field treatment of material originally treated with any waterborne treatment as long as this condition is met. Solutions shall have a minimum concentration of 1.5% (B₂O₃ basis)