A new study from U of T Engineering shows that unless construction practices change, Canada cannot simultaneously meet its targets for both new housing and emissions reductions.

“Our analysis shows that in 2018, which is the latest year for which we have the data, the construction sector in Canada was responsible for the equivalent of 90 megatonnes of CO2,” says Professor Shoshanna Saxe (CivMin), one of the senior authors of the study published in Environmental Research: Infrastructure and Sustainability.

“That was about 8% of Canada’s total emissions at the time, but we were not producing nearly as much housing as we needed then, let alone what we need now. To restore housing affordability, we need to triple the rate of housing construction by 2030.

“At the same time, our greenhouse gas emissions target for 2030 is to be 40% below 2005 levels, which works out to only 443 megatonnes in total. That means that unless things change, by 2030 nearly half of all the allowable emissions in Canada would be due to construction alone.”

Saxe directs U of T Engineering’s Centre for the Sustainable Built Environment (CSBE), which launched in 2023. Its mission is to research the construction and urban design pathways that will enable Canada to build the housing and infrastructure that it needs while reducing greenhouse gas emissions in line with the Paris Agreement.

Quantifying the scale of this challenge is the first step, but the CSBE team found that this calculation was not as straightforward as they anticipated.

“We thought that data on the construction industry’s carbon footprint might be somewhere in the Intergovernmental Panel on Climate Change reports that Canada submits to the United Nations,” says Saxe.

“What we found was that this data is split across many different parts of the economy: manufacturing, buildings, transportation, etc. There are also questions around consumption versus production: if a piece of steel is made in China and used for a building in Canada, whose emissions are those?

“Until now, it’s been difficult to get a picture of the construction sector as a whole, which is partly why it’s been overlooked.”

Hatzav Yoffe, a postdoctoral fellow working with Saxe and lead author on the paper, used an approach known as an environmentally extended input-output (EEIO) model to conduct a high-resolution, top-down analysis of Canada’s national construction sector.

The other members of the team included Keagan Rankin (CivMin PhD student), Professor Daniel Posen (CivMin) and Professor Christian Bachmann of the University of Waterloo. The full paper can be read on the CSBE website.

In addition to the top-line numbers above, the team calculated that residential construction — that is, homes — was responsible for the largest share of total construction emissions at 42%.

The model they constructed also enabled them to ask another question: given the expected increase in housing construction, how much would emissions per constructed home have to decrease in order to stay within emissions targets?

“You can’t just take the overall 40% reduction target and apply that to the construction sector. That won’t be enough, because you are also tripling the rate of housing construction,” says Saxe.

“We found that if we are to stay within our emissions budget, homes built in 2030 will have to produce 83% fewer greenhouse gases during construction than those built in 2018.”

While the study throws the tension between Canada’s housing targets and its climate targets into sharp relief, Saxe and her colleagues believe it is still possible to reconcile the two.

“There are a lot of different ways to approach this challenge, all of which we are exploring in our research,” she says.

“For example, if you build more densely, you use fewer materials to build the same number of units. If you are strategic about where you place those units, you don’t have to build as many new roads, or sewers to service them. We can also think about changing the balance between housing construction and other types of infrastructure, such as oil and gas infrastructure.

“At the end of the day, if we’re going to build what we need while avoiding the most catastrophic impacts of climate change, we need to seriously think about how we can deliver more with less.”