Updated: Aug 16, 2020
Despite the flooding on the Ottawa and Gatineau rivers in 2017 and 2019, I'm not really concerned about rivers flooding: I'm way more pumped about solving flooding from other sources.
In my previous life as a contractor I worked on a house that was actually a converted cottage that had been built on blocks. The hill directed spring rains into the house some years so I built a catch basin and installed a 24-inch culvert under the middle of the house. Presto! Water problem solved. You might think a full basement would solve the problem but a basement may not have parted the waters. It's hard to make a basement waterproof, and water is sneaky. That wasn’t so bad when I was a kid: the basement was for hockey and millipedes (which give me the willies to this day). Now people finish, furnish, flood and repeat.
Flooding is the costliest insured loss in Canada. The Insurance Bureau of Canada (IBC) claims the average cost to repair a flooded basement is over $40k. That's because we finish our basements and use them as living space more and more. It's also because we’re getting more rain events here, especially on frozen ground in the spring. We generally don't build our homes to manage that much water. In the past insurers and governments paid for these repairs. Since 2015, some (not all) insurers have offered "overland flood insurance" as an extra rider on your property insurance policy. This is how insurers and governments are trying to transfer flood risk from all insured homes and all taxpayers to higher risk home owners only. You might want to ask your insurance broker if you're covered. And if your basement flooded in the past that overland flood rider might get really expensive, or even denied. Could be that nobody bails you out next time.
In the Hills we build on steep slopes, by lakes, and near placid creeks that become torrents in the spring. I’ve heard people say “Yah we get water in the basement. It’s not a big deal”. Many homes here have sump pumps and I’ve seen gutters built into basement floors. This might seem logical except water infiltration can create rot and mold, ruin your stuff and make your house unsafe. Get it out pronto with a pump, wet vacuum, fans and dehumidifier. But it’s best to stop it from entering in the first place. Infiltration is often hard to diagnose. If water’s coming in from under your basement floor, or the water table is really high at your home, you might be stuck with it (because the solutions can be really expensive). That's when you deal with infiltration inside the house. However, in my experience most water in basements comes from above ground. Think of it this way: if your basement gets wet when it rains and/or during the early spring melt, that water's likely coming from the surface, yes? There are expensive solutions like excavating and waterproofing the whole foundation, but sometimes the solutions are really simple. Here are a few.
First, especially during hard rains or when it rains on frozen ground, ensure that water goes away from your house rather than towards it. This often means evaluating your grading - preferably before a downpour! - and simply adding wheelbarrows of soil and some grass seed at the foundation. Backfill settles over time, changing the grade at the house and directing water to the foundation. There are a bunch of other simple things you can do. I can't go through them all but here are some:
remove barriers like garden borders that prevent water from escaping;
keep trees away from the house because they can cause foundation problems;
install window wells with plastic covers on windows close to grade;
On a slope, build berms or shallow trenches uphill to direct water around the house;
make sure you have footing drains (also called weeper or drain tiles), and that they're functioning properly
Here's another easy but non-obvious solution: during the spring melt, If we have lots of snow, and especially if you shoveled your roof, dig channels so melt water and rain water can get away from the house. Note that foundation walls can transfer heat outside, melting frozen earth against the wall, and allowing water to get to the footing and into the basement. That’s one reason why footing drains are building code mandatory for foundations. My biz partner Jean has a neat trick: he lays roof heating cables perpendicular across the pile of snow. Overnight, voila! there's a trough melted right to the ground so melt water can escape.
If you’re planning a new house, first check if the lot has flooded in the past. Insurers are fish out of water when it comes to a home in a marsh. Some other tips:
Design roof slopes to shed water downhill, and build large roof overhangs to keep water away from your house (and protect windows and doors and keep summer sun out too);
Raise your foundation, door sills and windows well above the finished grade;
Make sure that your lot grading is designed from the start to direct water away from your house;
Have your builder compact the material as they backfill your foundation (S/he will know what I mean);
Use backfill like sand or "pit run" (sand/stone mix) that drains water rather than clay soil which holds water;
Ensure footing drains are properly installed around your foundation;
Install a water barrier under the concrete floor slab, and insulation while you’re at it.
These are basic best practices, and any good builder worth his or her salt water will use them. But basements are sort of old school now. If your builder wants you to have a full basement, make some waves, tell him his argument doesn’t hold water like basements do, and test the waters for slab on grade construction, which makes way more sense in many cases....because every day a little rain must fall!