# A Primer on Climate Zones for Home Construction in Canada

###### Shawna HendersonMay 19, 2021

Article updated July 2024

Understanding these climate zones is crucial, especially as climate change continues to impact weather patterns and temperature extremes across the country. We see houses as static things - we definitely don't like it when they move about!

But in fact, while the best houses don't move much, they are very dynamic. The house-as-a-system approach considers all components of a house. The building envelope is affected by temperatures, inside and outside, on daily, seasonal, and annual cycles. Temperature fluctuations and cycles are accompanied by humidity inside and outside.

### What's your delta T, good buddy?

Temperature differences between a comfy indoor environment and the exterior drive heat loss and heat gain. The rate at which this happens is relative, but is always fastest the bigger the difference between the indoor and outdoor temperatures. Building science nerds toss around the term 'delta T' when talking about energy loads and heat transfer. 'Delta' (∂) is the Greek letter that is used in math to indicate that the number represents the difference between two other numbers.

Like this: if it's +20°C inside and -20°C outside, the difference between those two temperatures is 40°C.

In a math formula, you would write that as:

∂T = Ti - To

∂T = 20 - (-20)

∂T = 40

Which translates into a written sentence as:

Delta T (the difference) equals T(inside) minus T(outside)

There's your nerd fix for the day.

You're welcome.

### Temperature and humidity: the siblings of discomfort

ANY WHO. The basis of energy conservation and efficient houses: you want to minimize the rate of heat transfer between inside and outside. We can use the delta T in equations that include the thermal resistance of building materials. That's how we figure out how much energy the heating and cooling system is going to have to provide to keep the occupants comfortable at 'design' temperatures.

### Wind: their insufferable tag-a-long cousin

Another climatic factor in keeping people comfortable in their homes is wind. Wind creates pressure differences which push and pull air in or out of the house, causing drafts. Infiltration and exfiltration are the biggest challenges when it comes to controlling the comfort levels in a house, because they in term drive what's known as the 'stack effect', where warm air is pulled up and out of the house. It's how you feed nice warm air into the coldest winter nights.

## Are there 1, 3, 4, 5, or 6 Climate Zones in Canada in 2023?

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.

(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.

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 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.

It's a complicated story, but in the end, just use a really good window. Because windows will always be the weakest element in a house.

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.

But Zone 8 locations range from 7000 to 12000 HDD. So there's really another subset of 5 climate zones, because that's as much difference in HDD as there is between Zones 4 and 7a.

Most Canadians live in Zones 4, 5, and 6 - the largest cities are in this lower band. Most of the middle of the continent is Zone 7A and 7B. And by far, the largest land mass is in Zone 8.

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)

There's also this great resource from NAIMA Canada that shows HDD for locations by province and climate zone.

Figure 3:

## Climate Types

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.

Figure 4:

### Different climate regions need different approaches to building assemblies

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.

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### Net Zero Energy for New Construction

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## It all comes down to the amount of BS you know

I mean building science.

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? It's much more than figuring out how much insulation you need.

### 7 issues that are driven by climatic conditions

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

### Extreme weather events mean we need to add resiliency to the mix

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. A holistic approach that considers factors such as climate types, average temperatures, and precipitation, means buildings are not only code-compliant but also energy-efficient and comfortable for their occupants.

Our work doesn't' stop there, though, we need to consider best practices for foiling wind, fire, and floods.