Codes and Standards

In Canada, use of treated wood is regulated by industry standards and by building codes. The Canadian Standards Association (CSA) produces the O80 series of standards for treated wood. The National Building Code of Canada (NBCC) is our model building code, adopted and/or modified for use by the various jurisdictions across the country. The NBCC contains requirements regarding the use of treated wood in buildings.

CSA O80 Series

The Canadian Standards Association is a private, not-for-profit organization certified by the Standards Council of Canada for the development of standards. The CSA Technical Committee on Wood Preservation oversees revisions to the O80 series of standards. This committee comprises representation from chemical manufacturers, wood treaters, government regulators, researchers, consultants and users of treated wood products. The CSA O80 series refers to a number of American Wood Protection Association standards for analytical standards and most preservative specifications.

Canadian standards for wood preservation are based on the American Wood Protection Association standards, modified for Canadian conditions. Only 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. Click Here for a list of products and associated Use Classes extracted from the CSA O80-08 Series of standards and reproduced with the permission of the Canadian Standards Association.  For more detail see CSA O80-08.

The current version of the Standard, CSA O80 series-08, has been revised into use class format comparable to the American Wood Protection Association standards but using the ISO 21887 Use Class system. Click here for a table of Use Classes and associated agents of deterioration, reproduced with the permission of the Canadian Standards Association.  For more detail see CSA O80-08.  The 2008 edition also contains a number of new provisions for residential treated wood products where preservative loadings do not need to be as high as the loadings required in industrial and commercial applications.  Many of the residential products in Groups A and B, such as guard rails or mill work cannot be incised (mechanically perforated to improve penetration) due to their size or profile. As well, customers often prefer that treated wood products in these groups, such as deck boards or railing components, are not incised as incising can detract from appearance and can lead to splintering.  Deep preservative penetration is not required for residential product groups A and B because these are either non-structural products, used where the potential for decay is low or used where the member does not provide support for another structural member.  Furthermore, these wood products are easily inspected  and their service life is typically limited by reasons other than decay.

National Building Code of Canada

In the 2005 edition of the National Building Code a number of additional references to preservative treatment were added and the previous requirements were clarified:

  • Pressure-treated wood must be used for wood elements in direct contact with the ground.
  • Sill plates are required to be treated if the vertical clearance to the finished ground level is less than 150mm and a damp-proof membrane is not used to separate the wood from the concrete.
  • In termite areas, pressure-treated wood is required unless the clearance to the ground below is more than 450mm and visible for inspection.
  • Crib-work or retaining walls more than 1.2 m high or supporting building foundations must also be treated.

The CSA O80-87 Series of standards are referenced in the 2005 code but the CSA O80-08 series will be referenced in the 2010 edition of the NBCC.  Preservative treated wood must be marked to indicate that it conforms to the relevant required treating standard.  A third-party quality assurance program for treated wood has recently been introduced by the Canadian Lumber Standards Accreditation Board.

As with all other requirements of the National Building Code, the NBCC references to pressure-treated wood should be regarded as requirements to meet minimum standards of performance. The NBCC does not cover all applications where pressure-treated wood may be used.

International Standards

Canadians also have a role in wood preservation standards development outside Canada. Several Canadians have, for many years, been active contributors to the subcommittees and task forces of the American Wood Protection Association standards committees. The secretariat of the ISO TC 165 Subcommittee 1, “Wood Materials, Durability and Preservation” was maintained by the Canadian Institute for Treated Wood. FPInnovations wood preservation scientist Paul Morris was chairman of that subcommittee.  This was the subcommittee that developed ISO Standard 21887, Durability of wood and wood-based products – Use classes.