Basement Flooding in Laval: River Floods, Spring Thaw, Sump Pumps and Backwater Valves

Three kinds of flooding on one island

Sewer backup arrives from below, through the floor drain or a basement toilet, during or just after heavy rain, and smells like sewage; older parts of Laval on combined or overloaded sewers see it in summer thunderstorms. Groundwater arrives at the wall-floor joint and through cracks and window wells during the spring thaw, when the ground is saturated and the water table rises; it is clear or muddy. River flooding is a different scale: the water table rises with the river, and no sump pump keeps up when the river is above your basement floor.

Photograph where the water first appeared and when, because the answer decides whether you need a plumber, a waterproofer, or the City’s flood measures and your insurer.

What the fixes do

A backwater valve, the clapet antiretour required on most Quebec homes under the plumbing code, is a one-way flap on the sanitary lateral that closes when the sewer surcharges so sewage cannot flow back into the house; while it is closed nothing drains, so do not run water during a storm. Many older Laval houses have one that has never been inspected; it needs a check and a cleaning, and the City of Laval has published requirements on backwater valves for homes at risk. A sump pump collects groundwater from the foundation drain and pumps it outside; a battery backup keeps it running through the outages that come with spring storms.

Grading and downspouts are the cheapest fix of all: extend downspouts well away from the foundation and make sure the ground slopes away from the house.

• Photos of where the water appeared and when
• Backwater valve located and its condition
• Sump pump tested and the discharge line clear
• Downspouts extended away from the foundation
• Insurance coverage checked for sewer backup and overland water

What Quebec requires of the plumber

Plumbing contractors in Quebec must hold a Régie du bâtiment du Québec licence and be members of the Corporation des maîtres mécaniciens en tuyauterie du Québec; both publish lookups, and a contractor who cannot give you an RBQ number is not allowed to do the work. Installing or replacing a backwater valve or sump system is plumbing work under the code and may need a permit from the City of Laval; ask the plumber which permit applies. Quebec’s Consumer Protection Act gives you a cancellation period on contracts signed with an itinerant merchant, which includes a plumber who came to your door after a flood.

Ask for the estimate and contract in the language you read, and for the warranty on the valve, the pump and the workmanship in writing.

Before the next spring

In March, lift the sump float and listen for the pump, then look outside: a discharge line frozen solid or buried in a snowbank sends the water straight back into the pit. Test the battery backup. Have the backwater valve inspected and cleaned. Check that sewer backup and overland water are both on your home policy; they are usually separate add-ons, and insurers ask whether a backwater valve is installed.

If you are in a river flood zone, the City of Laval publishes flood maps and seasonal advice, and the province’s disaster financial assistance program applies after a declared flood. Those are the tools for river flooding; a bigger pump is not.