Determining ASHRAE 90.1-2010 Climate Zones Bulletin

ASHRAE 90.1-2010 Energy Standard for Buildings Except Low-Rise Residential Buildings requirements are based on the environmental conditions of the proposed building location. ASHRAE 90.1-2010 requires four climatic values to define the environmental conditions of a proposed building location:

  • Heating Degree-Days below 18°C
  • Cooling Degree-Days above 10°C
  • Monthly Mean Temperature
  • Monthly Precipitation

Thresholds for each of these climatic values have been established in order to group environmental conditions into various zones. Table B-4 International Climate Zone Definitions in ASHRAE 90.1-2010 (see Appendix) provides the calculation formula for establishing Climate Zones based on these four climatic values. The assigned Climate Zone dictates energy efficiency requirements appropriate to the locations.

The BC Building Code states that the authority having jurisdiction (AHJ) can establish climatic values1 for use in the calculation formula provided in Table B-4. A common approach is for AHJs to use Heating Degree-Days below 18°C from listed locations (or in the absence of a specific listing, neighbouring locations) within Table C-2 Design Data for Selected Locations in Canada of the BC Building Code, and apply them broadly to all construction within their jurisdiction2.

Values for cooling degree-days above 10°C, monthly mean temperature, and monthly precipitation however are not provided in Table C-2. These values can be modelled by Environment Canada based on latitude and longitude as a fee-based service. Alternatively, the AHJ can obtain raw climatic data from select weather stations (available on Environment Canada’s website:, and map appropriate values based on geographic proximity and local experience. It would be reasonable if an AHJ established a set of these three values and likewise apply them broadly within their jurisdiction.

If the AHJ chooses not to establish climatic values, the building designer must obtain the climatic values by selecting the appropriate values from Table C-2 of the BC Building Code and by contacting Atmospheric Environment Service, Environment Canada, 4905 Dufferin Street, Toronto, Ontario M3H 5T4, 416-739-4365.

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