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Just like lumber, softwood plywood for structural sheathing applications can be pressure treated with preservatives. The deep penetration of a preservative provides protection against decay and insect attack. Pressure-treated plywood is used in a variety of applications: for termite and decay resistant roof, wall and floor sheathing, raised floor systems, permanent wood foundations, bulkheads, retaining walls, concrete forms, swimming pools, highway noise barriers, irrigation structures, cooling towers, transport and storage containers, floating docks, planters, and many others.
Properly treated according to American Wood Preservers Association (AWPA) standards, pressure-treated plywood maintains its strength and stiffness, thermal properties, workability, light weight and economy. To assure proper treatment, plywood should be treated according to appropriate AWPA standards. The preservative treatments are recognized in the model building codes, as well as in federal, military and AASHTO specifications. Standard panel dimensions are four by eight feet; some mills produce panels nine or ten feet, or longer.
The same preservative retention levels for chemical treatment used in termite and decay-resistant lumber framing should be used for treated plywood sheathing. Treated plywood used in residential and commercial buildings should be kiln dried after treatment (KDAT) to 18% moisture content or less.
Finishing recommendations for pressure-treated plywood are generally the same as for untreated plywood. For best results, plywood products treated with waterborne preservatives are readily paintable when KDAT. Painting plywood treated with creosote or oil-borne preservatives such as pentachlorophenol is not recommended.
NOTE: If structural sheathing material desired is Oriented Strand Board (OSB), waterborne treatments such as CCA or ACZA are not applicable. However, OSB treated with zinc borates for resistance to Formosan termites is available in the Southeastern U.S.
For more information on plywood products, go to APA.
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