Researchers at the University of Toronto say that basements are costly for the environment.

Real estate construction is a big producer of carbon emissions. According to the Global Alliance for Buildings and Construction, the largely grounded transportation industry produced 23 per cent of global carbon emissions in 2020. Compare that with 38 per cent of global carbon emissions in 2020 that came from building construction.

That number accounts for emissions produced during construction as well as ongoing emissions from natural gas heating or coal-powered electricity.

According a report from a team at U of T engineering, the bigger the build and more concrete poured into basements, the more taxing such housing becomes on the environment.

“Simply put, you should build as small as you can for what you need, and if possible, you should avoid having a basement,” professor Shoshanna Saxe, told U of T Engineering News.

She is the senior author of a new paper published in Resources, Conservation and Recycling called Capturing variability in material intensity of single-family dwellings. The case study focuses on Toronto real estate construction, specifically 40 single-family homes that were built between 2020 and 2021. The study analyzed which materials and how much were being used and their impact on the environment.

“What we found was that concrete basements were by far the largest driver of material use, accounting for an average of 56 per cent of the total material intensity,” says the study’s lead author Aldrick Arceo. “In terms of greenhouse gas emissions, the picture gets even worse, because concrete is carbon-intensive – a lot of emissions get created during its manufacture. This is in contrast to other materials such as wood, which is theoretically carbon neutral.”

In general, the researchers found that the larger the home, the more damaging it is to the environment, because there are more materials being used as well as more energy costs associated with heating larger bedrooms and living rooms. And single-family homes – which are the dominant form of housing construction in real estate markets outside of Toronto – do more damage by spreading out instead of building up. Basements are particularly appealing for buyers who plan to utilize the extra space for rental income.

So what are the solutions?

The U of T researchers stress that municipal zoning rules should consider these factors when permitting construction for single-family homes versus multi-unit residences. And the issue is particularly urgent as the Ontario government and real estate industry lobbyists push for more building on the Greenbelt surrounding Toronto.

“In a lot of areas, taller buildings are prohibited, as are buildings that come too close to the edge of the property,” says Arceo. “These kinds of rules incentivize underground construction. Basements are no longer just the foundation, they are designed to be part of the living space.”

@nowtoronto