In Canada, use of treated wood is regulated by industry standards and by building codes.
National Building Code
Specification of Treated Wood
The 2015 National Building Code of Canada (NBCC) mandates the use of treated wood in the following applications.
- Structural elements situated less than 150 mm from the finished ground level, or where they are not protected from exposure from precipitation, or moisture accumulation.
- In termite areas, unless the clearance to the ground below is more than 450 mm and visible for inspection.
- Crib-work or retaining walls more than 1.2 m high or supporting building foundations must also be treated.
Treated wood used in these applications must meet the treatment criteria specified in the CAN/CSA O80.1.
Treated wood is often used in many other applications not covered by the NBCC. Specification CSA O80 standards is a good way to help ensure that treated wood will meet performance expectations. However, it is not always necessary and may be difficult to obtain for some commodities. Specifiers should focus on wood species that are treatable, and in ensuring that the wood has been appropriately seasoned prior to and after treatment. Preservative retention and penetration are important indicators that should be specified to ensure treatment quality. The use of a third party quality assurance agency can help to ensure that materials meet specifications. After construction, the protection of cuts and holes with a field cut preservative should be specified.
Further guidance is available in the AWPA standard M1, Standard for the purchase of treated wood products.
CSA O80 Series Standard
The Canadian Standards Association (CSA) produces the O80 series of standards for treated wood.
CSA O80 Series includes “Use Classes”, which specifies a required preservative penetration and retention based on the exposure condition. Exposure conditions include UC1 (dry interior), UC2 (dry interior but could be exposed to dampness), UC3 (exterior construction but not in contact with the ground), UC4 (exterior construction with ground contact), and UC5 (wood used in coastal waters).
