Basement apartments should be banned in flood-prone areas, Montreal official says

A flooded basement in Montreal. The Insurance Bureau of Canada reports that the remnants of Hurricane Debby, which struck southern Quebec on August 9 and 10, 2024, were the costliest weather event in Quebec's history. (Graham Hughes/The Canadian Press)

Basement apartments should be banned in certain parts of Montreal to prevent them from being flooded during severe weather events, a city official told residents at a council meeting Monday night.

Weeks after remnants of Tropical Storm Debby brought torrential rain to Montreal last month, the city's head of water infrastructure heard from frustrated residents whose homes were flooded when sewers backed up from record-breaking rain.

Maja Vodanovic, who sits on Mayor Valerie Plante's executive committee, said boroughs will be able to pass their own bylaws banning the construction of basement apartments.

The Ville-Marie borough has already made regulatory changes to prevent the construction of new dwellings below street level in flood control zones.

"This is what we thought, right? Build as much as you can, and we've permitted apartments in the basements, but people who are flooded two, three times don't think it's a great idea," Vodanovic said in an interview Tuesday.

She said it's necessary to make these bylaws due to the threat posed by severe weather events caused by climate change.

For existing buildings that have basement dwellings, Vodanovic said owners should consider using tile flooring instead of carpets and take other steps to prevent significant losses. A recently expanded city program, RénoPlex, provides residents up to $20,000 for a one-unit building (or up to $40,000 for multi-unit dwellings) for the purchase of sump pumps, check valves and other renovations to make homes better protected from water damage.

According to the Insurance Bureau of Canada (IBC), the Aug. 9 storm that hit Montreal was the costliest severe weather event in Quebec's history — even worse than the 1998 ice storm. The flooding led to $2.5 billion in insured losses, the IBC said in its preliminary assessment last week.

André Gagné, a professional building inspector and expert in building construction, agreed that basements shouldn't be used as living spaces.

"We are building basements the same way we built back in the 1960s: concrete walls, French drain around the foundation, maybe a sewer system by gravity or maybe the water goes in a sump pump," he said in an interview with CTV News last month.

What about the city's infrastructure?

The City of Montreal website provides a map of areas that are prone to the effects of climate change, including heat islands and flooding.

When asked if the city should prioritize upgrading its sewer infrastructure, Vodanovic said it's not that simple.

"Even if we rebuilt all the sewer systems in Montreal, that would cost, like, $10 billion and imagine how many years it would take, it would still be not enough because you can't build sewers big enough to contain all that water," she told CTV News.

More than 150 millimetres of rain fell on Aug. 9, smashing a previous record set in 1996. The monthly average rainfall for Montreal in August is about 94 millimetres.

On Monday, the city council also adopted a unanimous motion calling on the provincial government to make changes to its financial compensation program for homeowners affected by weather-related flooding.

The premier has previously said the government may expand it to include sewer backups, which has been excluded. The program only compensates for damage caused by overland flooding but was never expanded.