Article updated 11 August 2023
Are there 1, 3, 4, 5, or 6 Climate Zones in Canada in 2023?
Let me explain.
First, let's talk about Degree Days. Heating Degree Days quantifies how much the temperature dips below 18°C in a year in a location. The higher the HDD value, the colder the winter temperatures are, and the longer the heating season. On the other hand, Cooling Degree Days indicate how much the temperature goes above 18°C in a year in a location.
(Just to make it complicated, in the US, HDD are based on 65° Fahrenheit, so if you're looking at US maps and HDD, you'll see different numbers.)
OK, to the maps!
This map breaks the country out into 4 zones, based on heating degree day (HDD) thresholds. The agricultural sector and the building industry rely on HDD for success in growing food and keeping people comfortable.
Energy Star Windows
The original Energy Star for Windows map showed the 4 HDD zones from Environment Canada, but this was changed to 3 zones, collapsing ‘Zone D’ (purple in Figure 1) and ‘Zone C’ (blue in Figure 1) into one zone. And, the zones were changed from letters to numbers. So: Energy Star Windows were rated for Zone 1, 2, and/or 3 in Canada. But then, there was a lot of confusion and complication about what windows got shipped where with which labels, so Natural Resources Canada changed again so that there’s one Energy Star label for windows in Canada. Each label is printed with detailed specifications showing performance levels for a specific window.
National Building Code
This is what matters when it comes to high-performance housing and being code compliant. There are 6 climate zones in Canada. They are based on HDD climate zones that encompass all of North America, and so, do not start at 1, or A. Canadian climates fall between Zone 4 and Zone 8.
Which is 5 zones.
But Zone 7 is split into Zone 7a and Zone 7b, making it 6 zones, see Figure 3.
Most Canadians live in Zones 4, 5, and 6. You can find a chart that lists the HDD for hundreds of cities and towns throughout Canada in the NBCC, Division B, Table C2. (NBCC 2020 can be downloaded for free here)
The NBCC point us to how much insulation to install, and how much heating or cooling is needed to keep occupants comfortable based on design temperatures and rate of heat transfer through materials. The Energy Star Window label tells us the performance of new windows based on a few key characteristics like solar heat gain coefficient. What neither of these tell us is best building practices based on the actual climate.
So let’s throw this into the mix as well.
North America has a range of 8 climate types that help us differentiate not only cold from warm, but also dry from humid. Figure 4 shows a simplified version of the Hygrothermic Regions Map from the US Department of Energy, which takes into consideration HDD, average temperatures and precipitation.
Building in a wet and cold climate is different from dry and cold, which is different from warm and humid. In Canada, we experience 4 of 8 hygrothermic regions: Marine, Cold, Very Cold, and Sub-Arctic/Arctic.
This is the reason why we can’t always rely on US-based information on best practices or applicable materials: it’s not always easy to tease out where the source information is intended to be relevant - an approach that works in a mixed humid zone doesn’t fit most regions in Canada, and an assembly that works in a hot-humid climate definitely will see some major problems in any part of Canada. This is also why some common US practices and materials are not compliant with Canadian building codes.
Understanding building science and how it relates to climate is a critical part of a successful whole house energy retrofit. But what kinds of building science-related issues are affected by climatic differences?
Here are a few top-level issues:
- Types of vapour retarder materials allowed and/or recommended
- Where the vapour barrier goes in an assembly
- Whether to use permeable or impermeable assemblies
- Whether to install an ERV or an HRV
- The location of the dew point and potential condensation within wall cavities on a seasonal basis
- Whether solar gain is good or bad as it relates to heating or cooling needs
- What solar heat gain coefficient to specify for windows in specific orientations
By designing for the future and retrofitting with climate in mind, buildings can be made more resilient and better equipped to handle changing temperature regimes. By taking a holistic approach and considering factors such as climate types, average temperatures, and precipitation, we can ensure that our buildings are not only code-compliant but also energy-efficient and comfortable for their occupants.