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If there was a comic book franchise about home ownership, water would be the super villain.

When water attacks, the damage includes stress, time, clean-up costs, higher insurance premiums and, possibly, a lower price if you sell your house. A study to be released Tuesday found an average 8.2 per cent reduction in the average selling price of a house if sold within six months of a catastrophic flood.

Climate change is driving more extreme weather patterns, which is in turn increasing the risk of flood damage for homeowners. That’s the story behind the new report from the University of Waterloo’s Intact Centre on Climate Adaptation. It’s called Treading Water: Impact of Catastrophic Flooding on Canada’s Housing Market.

The study tracked the effect of catastrophic flooding in five cities from 2009 to 2020: Grand Forks, B.C., Burlington, Ont., Toronto, Ottawa and Gatineau. Catastrophic is a term that sounds a bit overcooked, like something out of a superhero movie. But it just means flooding that resulted in more than $25-million in insurable claims.

The effect on real estate values in flooded areas of these cities was measured by comparing sale prices in the six months after the flood against the previous six months, and comparing nearby homes not affected by flooding.

Price declines in the five cities ranged from 1.1 per cent to 17.1 per cent at worst. The overall average of 8.2 per cent is equivalent to a loss of $58,507 on the national average Dec. 31 resale price of $713,500.

“We refer to that as a flood discount, and not in the positive sense,” said Kathryn Bakos, director of the Intact Centre’s climate finance and science program.

The study also found that houses where severe flooding occurred took an extra 13 days on average to sell, a 20 per cent increase on the national average period of 65 days. The number of houses for sale in the six months after a flood was down 44.3 per cent.

Ms. Bakos theorized that the drop in listings was a result of people waiting for the flood stigma to pass. A future study by the Intact Centre will examine the longer-term impact of flooding on home prices, but there’s already some research on this topic.

“Some studies suggest that rebounding could happen shortly after the six month time frame,” Ms. Bakos said. “Other studies show it could actually take three to five years, if at all, for to rebound.”

Who’s vulnerable to flooding? The study says about 3.3 million people, or 9 per cent of the population, live in an area where there is a significant flood risk. Moreover, these areas of risk are expanding as a result of extreme rain driven by climate change and the loss of forests and grasslands that help absorb water.

Home buyers, what does your list of desirables look like? Proximity to good schools and transportation, a walkable neighbourhood, an updated furnace and a nice kitchen are all important, but assessing flood risk is also important if you want to protect the value of your home.

Ms. Bakos said there’s a dire need for widely available, up-to-date flood mapping for home buyers and others. For now, a group called FloodSmart Canada has a website that offers flood maps for each province. You may be able to find information on a specific city or neighbourhood. Also try a Google search for flooding plus the name of a neighbourhood or city.

For homeowners, the Intact Centre offers an infographic that lists three steps for home flood protection – cost-free steps like cleaning your eavestroughs, affordable ones as in extending downspouts away from your foundation, and more complex steps like installing a backwater valve and sump pump.

Separately, there’s also an app to help manage the risk of water damage. It’s called Eddy and it connects your smartphone to sensors in your home that measure both your household water consumption and the presence of water in places such as the basement floor and other key points. The cost of this service, including 24-hour monitoring of your sensors by Eddy itself, is around $30 a month. This can be offset to some extent by discounts some insurers are offering to Eddy customers.

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