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:
A) Part 9 Treating requirements for wood members at or near ground level (Articles 126.96.36.199. Protection from Decay and 188.8.131.52 Protection from Dampness):
B) Part 9 treating requirements for buildings in localities known to have termites (Article 184.108.40.206 Termite and Decay Protection):
C) Treating requirements for wood members that are not protected from exposure to
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 220.127.116.11. Termite and Decay Protection):
B) Part 4 treating requirements for wood used in foundations (Article 18.104.22.168. Preservation Treatment of Wood):
Environmental Separation Requirements for Larger Buildings (Part 5) (Clause 22.214.171.124. 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.