Basement floor drain backing up: causes and what to do

Why it shows up at the floor drain

The basement floor drain connects to the same pipe that carries everything else out of the house. It is the lowest opening on that pipe. When the line is blocked or the sewer outside is full, waste water takes the easiest way out, and that is up through the floor drain. A basement shower, toilet or laundry tub may follow.

Step one: stop adding water

• Stop flushing toilets, running taps, showers, the dishwasher and the washing machine
• Tell everyone in the house
• If water is rising quickly, keep clear of it and switch off power to the basement if the panel can be reached safely

Work out which problem you have

It backs up when you use water. Running the washing machine or draining a bath pushes water up through the floor drain. The blockage is in your own building drain or in the lateral that runs from the house to the street.

It backs up during heavy rain or snowmelt, when no water is being used. The municipal sewer is overloaded and water is being forced back up your lateral. Neighbours may have the same thing.

It backs up in dry weather with nothing running. A blockage in the city main may be sending other people’s waste water your way. Call the municipality.

Only the laundry tub or one fixture overflows, and the floor drain takes the water away. The clog is in that fixture’s branch, not the main.

Clear water wells up with no sewage smell. This may be ground water coming through the weeping tile connection, particularly if the sump pump has failed.

Who to call

• A plumber or drain company, for a blockage in your own line. Ask for a camera inspection as well as clearing, so that you know the cause.
• The municipality. Most Ontario cities ask residents to report a sewer backup, and many will send a crew to check whether the problem is on the city side. In Toronto, for instance, this is done through 311.
• Your insurer or broker.
• A restoration contractor, if sewage has spread across the floor or reached finished areas.

Responsibility for the lateral is usually split at the property line. The homeowner looks after the private side and the municipality the public side, though the details vary by municipality.

What causes blockages on the private side

• Tree roots entering old clay pipe at the joints. This is the classic cause in older neighbourhoods.
• Collapsed, cracked or sagging pipe
• Grease poured down kitchen drains, which sets hard further along
• Wipes, paper towel, sanitary products and other things that do not break down
• Debris in the floor drain trap itself: lint, dirt and sand
• A stuck or failed backwater valve

Is the water dangerous?

Assume so. Water coming up a floor drain has been in the sanitary sewer. It can carry bacteria, viruses and parasites.

• Keep children and pets out of the basement
• Wear rubber boots, gloves and eye protection
• Do not use a household vacuum
• Wash thoroughly afterwards
• Throw out any food and medicine it touched

Cleaning up

A small spill on bare concrete can be handled by a careful homeowner: remove the water, wash the floor and the base of the walls with detergent, apply disinfectant for its full contact time, and dry the area with fans and a dehumidifier.

Call a professional when sewage has reached carpet, drywall, panelling or stored belongings, covered a large area or stood for more than a short time. Porous materials that absorbed sewage cannot be reliably cleaned and are removed: carpet and underpad, the lower part of drywall, insulation, particleboard furniture and cardboard. The structure is then cleaned, disinfected and dried.

Full steps: sewer backup: what to do.

The floor drain itself

Trap primer and dry traps. The floor drain has a U-shaped trap that holds water to block sewer gas. If the drain is rarely used, the water evaporates and the basement smells of sewer. Pour a litre or two of water into it every month or so.

Cleaning. Lift the grate and clear lint and debris. Laundry lint is a common cause of slow floor drains.

Do not seal it permanently. The floor drain is there to remove water from a leaking water heater or a burst pipe. Plugging it stops backups and leaves the basement with no drain. A backwater valve is the proper answer.

Preventing the next one

• Backwater valve. Installed on the main drain, it closes when flow reverses. It needs a plumbing permit and periodic cleaning. See backwater valves in Ontario.
• Camera inspection of the lateral, particularly in a house with clay pipes and mature trees
• Root cutting or lining of a damaged lateral, or replacement
• Disconnecting downspouts and weeping tile from the sanitary sewer where your municipality allows or requires it
• A sump pump with backup to handle ground water separately
• Grease in the bin, not the drain
• Nothing but toilet paper down the toilet

Several Ontario municipalities subsidise backwater valves and related work. Check your municipality’s current program before starting.

Insurance

Sewer backup is not part of a standard home policy. It is an endorsement you add, with its own limit and deductible. With it, cleanup and repairs after a backup are commonly covered. See sewer backup insurance in Ontario.

More: sewage backup cleanup.