Why does the basement leak after heavy rain or a thaw?
The basement is dry all year, then a downpour or the March thaw puts water on the floor. Where it is getting in, what the City of Toronto tells homeowners to fix outside, and what to do about what is already wet inside.
Water on the floor now? Call 647-697-7435, answered 24 hours
Rain and meltwater take the lowest path into a house. In a basement that usually means a window well full of water, a downspout emptying beside the wall, ground that slopes toward the house instead of away from it, or a crack in the foundation. The City of Toronto lists each of these. Dry the basement first, then fix the outside before the next storm.
This is a different problem from a burst pipe or a sewer backup. The water is coming from outside the foundation, so it will keep coming every time the weather repeats until the outside is fixed.
Where is the water getting in?
Look at where the water appears and when. A leak that shows up at the bottom of a window after rain points to the well. A damp line along the bottom of one wall points to downspouts or grading on that side. Water rising through the floor or at the joint between the wall and the floor points to groundwater around the whole foundation.
The City of Toronto's basement flooding page lists the causes of seepage from stormwater or groundwater: cracks or leaks in the foundation, walls, basement windows and doors; poor lot grading or drainage; failure of the weeping tile; sump pump failure; overflowing eavestroughs; and leaking or plugged downspouts.
| Where the water shows | Likely source outside | First thing to check |
|---|---|---|
| Under or around a basement window | Window well filling up | Well drain, leaves, snow piled in or against it |
| Along the bottom of one wall | Downspout or grading on that side | Where the downspout ends, which way the ground slopes |
| A single wet streak down a wall | Foundation crack | The outside wall at the same spot |
| Wall-floor joint or across the floor | Groundwater, weeping tile or sump | Is the sump pump running and keeping up? |
| Only when the eavestrough overflows | Blocked eavestrough | Gutters full of leaves or ice |
| Up through the floor drain | Not seepage. A sewer backup | See sewer backup clean-up |
What does the City of Toronto tell homeowners to fix?
The City's how to prevent basement flooding page sets out the outside work, most of which costs effort more than anything else.
- Downspouts. Clear eavestroughs and downspouts of leaves, snow, ice and debris. Where downspouts are disconnected from the sewer, check they drain properly, ideally two metres from the foundation walls, according to the City, and without causing problems for neighbours or pooling on sidewalks and driveways. The City's basement flooding page says disconnecting downspouts from the sewer system is mandatory.
- Grading. The City says to ensure the grading around your home slopes away from the foundation wall.
- Window wells. Seal cracks or leaks in window wells, and keep melting snow away from them.
- Cracks. Seal cracks in the foundation, walls and floors, and keep melting snow away so it cannot seep through them.
- Sump pump. Keep it working during storms and power outages, maintain it, and consider a back-up power source.
The City's Basement Flooding Protection Subsidy Program helps owners of eligible homes with part of the cost of a plumbing assessment, backwater valves, a sump pump and battery backup, and foundation drain severance and capping. The program page says downspout disconnection is not eligible for a subsidy, and window well covers and grading are not on its list. Conditions apply, so read the page before you book a contractor.
Outside of Toronto the same physics applies. In Barrie and the snowbelt north of the city, the thaw usually arrives with more snow against the walls.
What do you do with the wet carpet and drywall now?
Get the water out, find out how far it went, and dry it properly before you worry about the outside. Fixing the downspout stops the next leak. It does not dry the underlay and drywall that are already wet, and those are where mould starts.
Health Canada says a house and its furnishings are less likely to grow mould if they are dried within 48 hours. Seepage makes that harder than a pipe leak, for two reasons. It often goes unnoticed behind finished walls until the carpet edge is wet, and it comes back with the next rain, so a basement that dried once can be wet again before anyone checks.
What helps right away:
- Lift rugs, boxes and anything cardboard off the floor.
- Pull carpet back from the wet wall if you can, and photograph it.
- Run a dehumidifier with the windows closed if it is humid outside.
- Mark the wet line on the wall with tape and a date, so you can see if it grows.
When it needs more than that:
- The carpet and underlay are wet more than a short way from the wall.
- The drywall is wet, soft or stained at the bottom.
- There is a smell, or the leak has happened before.
- The water is still coming in.
What we do is extract the water, take moisture readings to map how far it travelled behind the drywall and under the carpet, remove baseboard and lower drywall where the wall cavity is wet, and run dehumidifiers and air movers until the readings show it is dry. We document it for your insurer as we go. Whether seepage is covered is a policy question: the Insurance Bureau of Canada says groundwater and seepage coverage are typically not standard across home policies.
How long for mould to grow after water damage explains why waiting for the next dry spell is the wrong plan, and the general order of events is in flooded basement: what to do.
What to do now
If the basement is wet now, call 647-697-7435. The line is answered 24 hours for water damage. We dry what is wet, show you how far the water went, and tell you where it appears to be coming in, so you know what to fix outside. The price is confirmed before work starts. The service is water damage cleaning and restoration, across Toronto and the GTA.
Short answers.
- Is a full window well an emergency?
- It can become one quickly. A window well holding water is pressing it against the window frame and the wall below it. Bail it out or pump it out, check the drain at the bottom is not blocked with leaves or ice, and move snow away from it. If water is already coming through the window or the wall, treat it as a leak and start drying inside.
- Does the City of Toronto subsidy cover window well covers or grading?
- No. The City's Basement Flooding Protection Subsidy Program lists a plumbing assessment, backwater valves, a sump pump, a sump pump battery backup and foundation drain severance and capping. Window well covers and grading are not on that list, and the program page says downspout disconnection is not eligible for a subsidy.
- Why does the leak only happen in spring?
- Because that is when the most water sits against the foundation at once. Snow piled along the walls melts, the ground below may still be frozen so the water cannot soak away, and spring rain arrives on top. The City of Toronto advises keeping melting snow away from window wells and the foundation for exactly that reason.
Filed under Water damage. More in the blog.
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