The treated wood you buy at your local building supplies store will have an end tag to help you choose the right product. The tag identifies the type of preservative used, the amount retained, the appropriate use for this piece of wood, and the treatment plant name and location. The most important information to look for is the use class. If the piece is going in the ground (e.g. a fence post), you need the piece to be treated for “ground contact.” All other uses (such as fence boards, deck boards and shingles) can be labeled “above ground.” The piece may also be tagged with consumer safety information. You might also find this information in the store, either posted or as a technical brochure.
The National Building Code of Canada (NBC) contains requirements regarding the use of treated wood in buildings and the CSA O80 Series of standards is referenced in the NBC and in provincial building codes for the specification of preservative treatment of a broad range of wood products used in different applications. The first edition of CSA O80 was published in 1954, with eleven subsequent revisions and updates to the standard, with the most recent edition published in 2015.
The manufacture and application of wood preservatives are governed by the CSA O80 Series of standards. These consensus-based standards indicate the wood species that may be treated, the allowable preservatives and the retention and penetration of preservative in the wood that must be achieved for the use category or application. The CSA O80 Series of standards also specifies requirements related to the fire retardance of wood through chemical treatment using both pressure and thermal impregnation of wood. The overarching subjects covered in the CSA O80 Series of standards also include materials and their analysis, pressure and thermal impregnation procedures, and fabrication and installation.
Canadian standards for wood preservation are based on the American Wood Protection Association (AWPA) standards, modified for Canadian conditions. Only wood preservatives registered by the Canadian Pest Management Regulatory Agency are listed.
The required preservative penetrations and loadings (retentions) vary according to the exposure conditions a product is likely to encounter during its service life. Each type of preservative has distinct advantages and the preservative used should be determined by the end use of the material.
Processing and treating requirements in the CSA O80 Series are designed to assess the exposure conditions which pressure treated wood will be subjected to during the service life of a product. The level of protection required is determined by hazard exposure (e.g., climatic conditions, direct ground contact or exposure to salt water), the expectations of the installed product (e.g., level of structural integrity throughout the service life) and the potential costs of repair or replacement over the life cycle.
The technical requirements of CSA O80 are organized in the Use Category System (UCS). The UCS is designed to facilitate selection of the appropriate wood species, preservative, penetration, and retention (loading) by the specifier and user of treated wood by more accurately matching the species, preservative, penetration, and retention for typical moisture conditions and wood biodeterioration agents to the intended end use.
The CSA O80.1 Standard specifies the following Use Categories (UC) for treated wood used in construction:
- UC1 covers treated wood used in dry interior construction;
- UC2 covers treated wood and wood-based materials used in dry interior construction that are not in contact with the ground but can be exposed to dampness;
- UC3 covers treated wood used in exterior construction that is not in ground contact;
- UC3.1 covers exterior, above ground construction with coated wood products and rapid run off of water;
- UC3.2 covers exterior, above ground construction with uncoated wood products or poor run off of water;
- UC4 covers treated wood used in exterior construction that is in ground or freshwater contact;
- UC4.1 covers non-critical components;
- UC4.2 covers critical structural components or components that are difficult to replace;
- UC5A covers treated wood used in Coastal waters including; brackish water, salt water and adjacent mud zone.
This CSA O80 Series of standards consists of the following standards, as follows:
- CSA O80.0 General requirements for wood preservation; specifies requirements and provides information applicable to the entire series of standards.
- CSA O80.1 Specification of treated wood; is intended to help specifiers and users of treated wood products identify appropriate requirements for preservatives for various wood products and end use environments.
- CSA O80.2 Processing and treatment; specifies minimum requirements and process limitations for treating wood products.
- CSA O80.3 Preservative formulations; specifies requirements for preservatives not referenced elsewhere.
- CSA O80.4 has been withdrawn.
- CSA O80.5 CCA Additives — Utility Poles; specifies requirements for preparation and use of CCA preservative/additive combinations for utility poles permitted by CSA O80.1 and CSA O80.2.
For further information, refer to the following resources:
CSA O80 Wood preservation
Wood Preservation Canada
National Building Code of Canada
Pest Management Regulatory Agency
American Wood Protection Association
ISO 21887 Durability of wood and wood-based products — Use classes
Click here for more information on performance tests done with treated wood.