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2010 NATIONAL BUILDING CODE OF CANADA (NBCC)
REQUIREMENTS FOR TREATED WOOD

Requirements for Housing and Small Buildings (Part 9)

Requirements apply where wood which may be subject to fungal decay or termite infestation is used in:

  • walls, floors and roofs
  • balconies, decks, and other accessible exterior platforms intended for occupancy
  • preserved wood foundations 
  • retaining walls or cribbing supporting ground that is critical to the stability of the foundation, and retaining walls or cribbing greater than 1.2 m (4 ft.) high

A) Part 9 Treating requirements for wood members at or near ground level (Articles 9.23.2.2. Protection from Decay and 9.23.2.3 Protection from Dampness):

  1. Preservative treatment is required for wood in ground contact.
  2. Except where exempted below, preservative treatment is required for wood members that are at or below ground level and framed into masonry or concrete.
    (Exemption –– Preservative treatment is not required where a 12 mm (1/2 in.) air space is provided at the end and sides of the wood member.)
  1. Except where exempted below, preservative treatment is required for wood members that are within 150 mm of the ground.
    (Exemption –– Preservative treatment is not required where the wood member is supported on concrete and separated from the concrete by polyethylene film or roll roofing or equivalent dampproofing materials.)

B) Part 9 treating requirements for buildings in localities known to have termites (Article 9.3.2.9 Termite and Decay Protection):

  1. Preservative treatment is required for wood members that are within 450 mm (18 in.) of the ground.  
  2. Preservative treatment is required where:
  • wood members are 450 mm (18 in.) or more higher than the ground and not all of the sides of the structure supporting the wood members are visible, or
  • wood members are 450 mm (18 in.) or more higher than the ground and barriers have not been installed to control the passage of termites.
    (Exceptions - Preservative treatment is not required where wood members are 18 in. or greater above the ground and the supporting members are exposed or wood members are 18 in. or greater above the ground and barriers have been installed to prevent the passage of termites)
 

C)  Treating requirements for wood members that are not protected from exposure to
precipitation (Article 9.3.2.9):

  • Preservative treatment is required where the moisture index is greater than 1.00 and the configuration is conducive to decay
    (Note that the Appendix to the Building Code describes configurations that are conducive to decay,  “There are many above-ground, structural wood systems where precipitation is readily trapped or drying is slow, creating conditions conducive to decay.  Beams extending beyond roof decks, junctions between deck members, and connections between balcony guards and walls are three examples of elements that can acculmulate water when exposed to precipitation if they are not detailed to allow drainage”.)

Locations with a moisture index greater than 1.00 include Coastal British Columbia, New Brunswick, Nova Scotia, Prince Edward Island and Newfoundland and a few locations in Quebec. There are very few locations in Ontario with a moisture index greater than one and Ontario has not adopted the treating requirements for wood members that are not protected from exposure to precipitation.

Structural Requirements for Larger Buildings (Part 4)

A) Treating requirements for buildings in localities known to have termites refer to the Part 9 requirements (Article 9.3.2.9. Termite and Decay Protection):

  1. Preservative treatment is required for wood members that are within 450 mm (18 in.) of the ground.  
  2. Preservative treatment is required where:
  • wood members are 450 mm (18 in.) or more higher than the ground and not all of the sides of the structure supporting the wood members are visible, or
  • wood members are 450 mm (18 in.) or more higher than the ground and barriers have not been installed to control the passage of termites.
    (Exceptions - Preservative treatment is not required where wood members are 18 in. or greater above the ground and the supporting members are exposed or wood members are 18 in. or greater above the ground and barriers have been installed to prevent the passage of termites)

B) Part 4 treating requirements for wood used in foundations (Article 4.2.3.2. Preservation Treatment of Wood):

  1. Preservative treatment is required for wood foundation members exposed to soil or air above the lowest anticipated groundwater table.

Environmental Separation Requirements for Larger Buildings  (Part 5) (Clause 5.1.4.2. Resistance to Deterioration)

A) Materials used in building components and assemblies that separate dissimilar environments, or in assemblies exposed to the exterior must be resistant to any mechanisms of deterioration that may reasonably be expected, given the nature, function and exposure of the materials and the exposure and climatic conditions in which they will be installed.

It would be up to the designer responsible for designing the building envelope to determine where treated wood is required.