Should Canada stop building basements?

The rise of basement bans

In recent years, municipalities have begun to respond to the heightened risk of flooding by imposing restrictions on basement construction. In June, the Ville-Marie borough of Montreal passed regulations that prohibit homeowners from converting basements into living spaces unless they waterproof the area to withstand heavy rains. This decision was made in response to increasing instances of floods that have affected the area.

For example, the remnants of Tropical Storm Debby in August 2023 caused significant flooding in southern Quebec, leading to damages totaling nearly $2.5 billion — the most expensive weather disaster in Quebec's history, surpassing even the infamous 1998 ice storm. Just a month after this event, Maja Vodanovic, the mayor of the Lachine borough in Montreal, proposed banning new basement apartments in areas at high risk of flooding. Vodanovic argued that building basements in flood-prone areas would only worsen an already foreseeable problem.

This approach is not without precedent. Craig Stewart, vice president of climate change and federal issues for the Insurance Bureau of Canada, noted that after flooding along the Ottawa River a few years ago, Ontario offered disaster relief funds to rebuild homes on the condition that they be elevated above flood levels. This type of regulation, which eliminates basements as flood risks, has been met with approval by many advocates concerned with the impacts of climate change.

Growing flood risks in Canada

Traditionally, basements were a common feature in Canadian homes because they helped place the foundation below the frost line, preventing the house from shifting during freeze-thaw cycles. However, this practice is increasingly questioned as flood risks grow. Environment Canada has reported that storms occurring once every century are now happening every 20 years in some places, and storms expected every 20 years may now occur every five.

Urban infrastructure is also aging, and it wasn’t designed for the growing population and wetter climate that Canada is experiencing. This has placed significant strain on drainage systems, leading to more frequent and severe flooding, especially in urban areas with older infrastructures, like Montreal and Quebec.

Bernard Deschamps, a former insurance industry professional with 35 years of experience, has highlighted that the risk of basement flooding has increased dramatically. Now pursuing a PhD at the University of Quebec at Montreal (UQAM), Deschamps advocates for regulations that limit basement construction in flood-prone areas. He emphasizes that basements in new constructions, especially in regions known to flood, simply don’t make sense anymore.

The environmental impact of basements

Basements pose not only a flood risk but also a significant environmental challenge. The concrete used to construct basements has a large carbon footprint. Shoshanna Saxe, a Canada Research Chair in sustainable infrastructure at the University of Toronto, has conducted research that reveals the high levels of greenhouse gas emissions tied to the construction of basements. According to her study, basements contribute to 56% of the material intensity — the volume of materials used — in new homes.

Saxe explained that new homes in Ontario are, on average, 25% larger than those built in the 1990s, with their basements growing accordingly. Some of these basements are large enough to house playrooms or feature nine-foot ceilings, which drastically increases the environmental cost of construction. She also pointed out that the larger the basement, the higher the risk of flooding due to its lower position relative to the water table, which increases water pressure on the building.

In addition to their environmental cost, Saxe argues that many basements are underutilized. Often, they are used for storage or parking, and in some cases, the number of parking spaces exceeds what is necessary. Without basements, homes would be cheaper and quicker to build, leading Saxe to question the continued construction of these flood-prone and carbon-intensive spaces.

Alternatives to basement construction

Despite the risks, some argue that basements are necessary to place a home’s foundation below the frost line, especially in Canada’s colder climates. However, Saxe suggests that alternatives, such as pile foundations, where homes sit on underground columns, can achieve the same goal without the need for basements. In many parts of the world, including the southern U.S. and Australia, homes are typically built without basements due to local soil conditions and higher frost lines.

Saxe also pointed out that in Toronto, new regulations have been implemented to encourage above-ground construction in multiplex buildings to reduce their climate impact. Similarly, Montreal’s Ville-Marie borough removed height restrictions to allow developers to compensate for the loss of basement space, ensuring that housing supply isn’t significantly affected.

For existing homes with basements, both Deschamps and Saxe advocate for protecting them through floodproofing measures. Preserving basements in these homes makes sense, they argue, as they do not require additional materials and provide valuable living space in areas where housing is scarce.

As climate change accelerates the frequency of extreme weather events in Canada, cities are faced with the challenge of mitigating flood risks and reducing carbon emissions. Banning basements in flood-prone areas is one such measure being considered, especially given the increasing cost of flood-related damages and the environmental impact of basement construction. While basements have traditionally been a functional part of homes in Canada, it may be time to reconsider their necessity in light of the evolving climate realities.

source: CBC