The check valve: a one-way trip for wastewater

It’s raining cats and dogs. Fortunately, you know the roof of the house can handle it, and the cladding on the exterior walls too. But could trouble come from beneath, from a sewer backup, for instance? Are you protected from calamity there as well?

Your answer can be yes if your home is equipped with the best protection against this mishap: a functional backflow protector. Installed on the main collector or on the drainage pipe connections, a check valve prevents wastewater from a municipal sewer overloaded by heavy rain from backing up into basements through plumbing fixtures or floor drains located at a lower level.

CAA-Quebec - Tips and tricks - Basement flooding
(Source: CMHC illustration)

This type of flooding usually causes serious damage and, inevitably, high costs. Examples include wall and floor insulation and covering that need to be replaced, structures that need to be stripped or demolished, and items soaked in filth, fit only for the trash. In the best of cases, the municipality or insurance company will pay. But there’s still the huge inconvenience associated with this hardship.

Discontent over compensation
Since 2006, municipalities have been able to escape all liability for damage caused to a building or its contents by a sewer backup. How? By means of bylaws making the installations of check valves compulsory. Building owners are given a minimum of one year to bring their buildings into compliance. As for insurance companies, some of them will require clients to install compliant anti-backflow systems in their buildings if they want to stay covered in this area after they have been compensated for this type of disaster.

However, the massive downpours that seem to be turning into periodic summer weather events are reason enough for prevention. 

Of course, you can also take the protection approach. If you own or rent a unit on a lower floor, or you have a storage locker full of valuable items in the basement of the building, you will have to add the “Sewer backup” endorsement (also called a “rider”) to your insurance policy. (Note, however, that insurers will sometimes refuse to add this endorsement if the building is in an area where the municipal infrastructure is acknowledged to be deficient.)

A close look at check valves
Remember first that there are different sorts of check valves. The most common are of the “normally closed” type. They are equipped with a flap gate that rises to allow the flow of wastewater from the house. The flap then closes to prevent a potential flow from the sewer to the house. Some of them are designed to protect only a single device, for instance a washing machine, while others will provide protection for several plumbing fixtures linked to the same drainage connection on the same floor, such as the basement.

To avoid preventing the air flow needed for ventilation of the network, it is prohibited to install this type of valve on the main wastewater drainage conduit of a house; in certain houses, a “normally open” type that closes only in case of backup can be installed.

Compliant, functional and accessible
To ensure that the check valve is in compliance and properly installed, the work must be handled by a plumbing contractor. A check valve must be placed so as to be accessible. An access door or removable panel must be installed when it is inside a wall or ceiling, or under a false floor.

At least once a year, regular maintenance must be conducted to ensure that no debris is lodged in the flap gate or its mounting, blocking the device’s operation or watertightness. The Corporation des maîtres mécaniciens en tuyauterie du Québec advises doing this check early in the summer season.

Step-by-step maintenance for horizontal check valves:

  • Remove the screw- or bolt-secured cover or access plug. (Note: If you have a cast-iron check valve with a bolted cover, you’re better off entrusting the job to a plumbing contractor.)
  • Remove the flap gate, clean it, and inspect the rubber seal ring; replace the gate if necessary.
  • Clean the gate mounting; it must be free of debris so as not to hinder the operation of the valve.
  • Reseat the gate in the proper direction, making sure there is nothing obstructing the flap motion.
  • Firmly screw or bolt the access plug back in place and replace the cover (if necessary).