A Primer on Climate Zones

A Primer on Climate Zones

Shawna HendersonMay 19, 2021

Are there 3, 4, 5, or 6 Climate Zones in Canada?

Yes.

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.

OK, to the maps! 

Environment Canada 

This map breaks the country out into 4 zones, based on heating degree day (HDD)  thresholds - see Figure 1. The agricultural sector and the building industry rely on HDD for success in growing food and keeping people comfortable.

These are the basis for another set of climate zones for windows, and correlate to another set of climate zones that encompass all of North America. This causes a fair amount of confusion in the industry as to what flavour ‘climate zone’ we’re talking about.

Figure 1:

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 are now rated for Zone 1, 2, and/or 3 in Canada, as shown in Figure 2. 

Figure 2:

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.

Figure 3:

Climate Types

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. The NBC Climate Zones point us to how much insulation to install, and how much heating or cooling is needed. The Energy Star Windows Zones tell us which characteristics are required for new window installations across the country.

Figure 4:

What they don’t tell us is best building practices based on the actual climate. 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.

What’s affected by climatic differences beyond HDD? Here are a few top-level issues:

  • Types of vapour retarder materials
  • Where the vapour barrier goes in an assembly
  • Whether to use permeable or impermeable assemblies
  • Whether to install an ERV or an HRV
  • Dew point and potential condensation within wall cavities
  • Whether solar gain good or bad as it relates to heating or cooling needs
  • What solar heat gain coefficient to specify

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