Is it time to ban basements?

It was shortly after Elizabeth Peloza had finished her basement — painted what was set to be her kid’s room, installed a new electrical panel — when a torrential downpour broke through her window and flooded it floor to ceiling.

The flash flood hit London in July 2024, where Peloza lives and works as a city councillor, and caused more than $940 million in insured damage to areas of southern Ontario. Over half a year later, she is still assessing the damage to her home that she learned won’t be entirely covered by insurance.

“I just had an electrical inspection this morning, I’m still working my way through it,” she said.

Many people in Canada have felt the impact of increased flooding in recent years: August of 2024 saw Hurricane Debby bring a record-breaking deluge to Quebec, resulting in an unprecedented $2.5 billion in insured damage; flooding from British Columbia’s 2021 atmospheric river shut down railway lines, closed highways and severely impacted farms and residents; and Nova Scotia experienced back to back years of fatal flooding in 2023 and 2024.

Mitigating the widespread damage caused by flooding can be complex, but one solution gaining momentum is banning basements. Basements are the first places to flood, and some researchers say continuing to construct them will lead to expensive repairs for homeowners and vulnerable living situations for basement renters. 

The Ville-Marie borough in Montreal has made the leap. In 2024, a bylaw banned basement dwellings in new buildings in flood-prone areas. Other flood mitigation measures were enacted at the same time, explained Stéphanie Turcotte, director of the urban planning and mobility department for Ville-Marie. The borough, located in central Montreal along the Saint Lawrence River, is working on rainwater management measures at the city level: sponge projects, which use plants to absorb rainwater, are moving forward, as are other drainage upgrades.

Other flood-risk areas should consider following Ville-Marie’s lead, says Ryan Ness of the Canadian Climate Institute. Communities could even take it a step further and ban basements entirely – not just habitable ones. It makes sense to ban basements in high-risk areas as part of the “growing realization that at some point, you can't fight nature,” he adds.

Scrapping basements bleeds into a larger conversation about climate adaptation and managed retreat, which is moving areas, or in some cases, entire towns from climate-vulnerable regions. As climate change worsens, most areas in Canada experience more rainfall and coastal communities see more frequent storm surges —both leading to flooding. By the end of the century, storms that were once every 20 years, are projected to occur every five. 

The best way to reduce that cost is to not build housing at all in areas with high flood risk, but there is a spectrum of risk, and Ness said in some areas, scraping basements could be a middle-ground solution. He notes that “the cost of basement flooding is just skyrocketing” and most damage from last summer’s flooding events in Montreal and Toronto were in basements. 

While banning basements might seem extreme, Ness notes there are places in North America that already don’t have them because of water levels. You won’t find basements in Louisiana and Florida, for example, which both have an average elevation of only about 100 feet above sea level. Some parts of the states are even below sea level —constructing basements in those regions would be a recipe for repeated, expensive repairs.

Basements were once more commonly used as storage areas, but people today increasingly finish their basements and rent them out, noted Ness. About one in six Toronto homes has a secondary unit, totalling 75,000 units. Flooding leaves renters in precarious situations because insurance held by landlords doesn’t cover tenants’ belongings or temporary relocation costs. 

There isn’t a bylaw preventing new basements in London, but people might not be allowed to add a secondary unit in their existing basements. The conservation authority in Ontario develops flood maps ,which “allows municipalities and conservation authorities to guide development away from flood-prone areas and also supports better emergency management and planning.” 

That means someone in a high-risk flooding area could be approved by the city to put a secondary suite in place, but stopped by the conservation authority, explained Peloza. She noted the difficult balance between the lack of affordable rental suites and the need to dial back basement dwellings facing an increased risk of flooding. 

There is also a need to spread awareness about flood risk to homes impacting resident’s ability to finish their basements. This is a shift, notes Peloza: recently updated flood maps will mean that “a portion of my ward...as the flood mapping changes, aren't going to be allowed a secondary dwelling in the basements of their homes if they want.”

Meanwhile, the federal government is working to address the impact of flooding with its recently tweaked disaster relief program. Created in 1970, the fund paid out over $8.5 billion as of 2023, with flood costs making up over a third of total funds since 2010. The government says it will now cover up to 40 per cent of costs associated with making buildings more resilient to extreme weather: a shift from its previously reactive approach.  

What to do with existing basements?

Banning basement suites from new buildings is forward-thinking and considers the impacts of climate change, but doesn’t help in situations where basements already exist. Flooding in basements can happen in different ways: heavy rainfall can cause municipal sewer systems to overflow, leading to flooding through basement toilets and sinks. Water levels can rise high enough that water comes in through windows and doors. 

There are community-level responses that reduce flooding: traditional infrastructure like dams, and nature-based solutions, like the ones announced by Ville-Marie. However, individuals can also help reduce the severity of flooding, notes Anabela Bonada, manager and research associate at the University of Waterloo’s Intact Centre on Climate Adaptation.

Some measures like removing debris, checking for leaks in plumbing, and testing sump pumps, are free, said Bonada.

The centre launched the home flood protection program in 2016, to educate people on potential insurance discounts and share flood-proofing tips.

There are what the centre calls “simple upgrades,” which cost $250 or less, such as installing higher lips on basement windows and putting in flood alarms. Then, there are more expensive moves, like converting paved areas to vegetation; installing a backup sump pump and battery; and installing a backwater valve, which stops the backup of sewage flooding into basements. 

A basement flooding grant program in London provides money for upgrades like backwater valves — a support that once had few applicants, but following the summer flash floods, is now over-prescribed, notes Peloza.

People are hesitant to spend money on upgrades unless they’ve already experienced flooding, notes Bonada. But those willing to follow the centres’ advice and spend some time and money, can prevent their basements from flooding, she said.

Bonada urges people to take note because climate change is broadening the number of areas likely to be hit by floods.

“Flooding will only increase, just like wildfire. Just from extreme rainfall events, the expectation across the board is that it can happen anywhere in Canada,” she said.

“So, whether it’s Vancouver, Toronto, or any town where you're like, ‘well, it hasn't flooded, or it doesn't tend to flood,’ — extreme rainfall events are making that much more likely.”

– With files from The Canadian Press