Preventing Basement Flooding

Outside the house

The first line of defence is keeping rain and snowmelt away from the foundation. Walk around your house during a heavy rain and watch where the water goes.

• Grading: soil should slope away from the walls for the first couple of metres. Low spots against the foundation collect water.
• Downspouts: extend them so they discharge well clear of the house and onto ground that drains away. Check whether your downspouts are still connected to the sewer; many Ontario municipalities have programs to disconnect them, so ask the Town about current rules.
• Eavestroughs: clean them in the fall so they do not overflow beside the walls.
• Window wells: keep them clear of leaves, and consider covers.

Sump and backwater

Houses with a perimeter weeping tile usually have a sump pit that collects groundwater and a pump that sends it outside. A healthy pump, tested regularly and backed up for power outages, is essential. Our sump pump checklist walks through the seasonal tests.

Sewer backup is a different threat. During intense storms, municipal sewers can surcharge and force water back up into the lowest drain in your home. A backwater valve fitted into the main sewer line closes when flow reverses. Read the backwater valve guide to learn how they work and how to look after one.

Inside the basement

Some simple steps inside limit the damage if water does get in:

1. Store valuables, documents and electronics on shelves rather than the floor.
2. Keep the floor drain clear and accessible.
3. Fit a water alarm near the sump, water heater and laundry area.
4. Check the water heater and washing machine hoses for wear.
5. Know where your main water shutoff is; see our guide.

Small cracks in a poured foundation can let water seep through. Those are a job for a waterproofing contractor rather than a plumber, but they belong in the same plan.

Insurance coverage

Home insurance policies treat water damage in several categories, and sewer backup or overland flooding often needs an add-on endorsement. Call your insurer and ask plainly what you are covered for. Some insurers want to know about a backwater valve, or a sump pump with backup power; keep receipts and photos of those installations.

If water does come in, our pages on basement flood plumbing and backwater valve installation explain what we handle. For signs of slower trouble, see hidden leaks.

Take a slow lap of the basement each season with a flashlight. Look along the walls, at the floor drain, under the stairs and around the water heater. Small changes are easier to spot when you look on purpose.