Homeowner guidePrevention
Backwater Valves Explained for Homeowners
Few devices do more to keep sewage off a basement floor than a backwater valve. This guide explains how it works, who needs one and how to look after it.
Interior of contemporary bathroom with round ceramic bathtub and sink and wooden cabinet in daytime.
- Short steps a homeowner can follow safely
- What to check before you pick up the phone
- Clear signs it is time to call a plumber
- Markham and York Region notes where they matter
- Licensing details confirmed when you call
- Residential
- Commercial
- Markham & York Region
The short version
- Homes with basement fixtures such as toilets, showers, laundry and floor drains.
- Homes in areas that have had sewer backups.
- Anyone with a finished basement.
- Homes where insurers recommend or require it.
What it does
The valve is fitted into the main drain under your slab. Day to day its flap hangs open and wastewater passes straight through. If the city sewer backs up, water tries to flow back into your home. The valve's flap closes and blocks it.
Types
| Type | Notes |
|---|---|
| Normally open | Recommended. Lets air and water flow, closes on backflow. |
| Normally closed | Not typically recommended for main lines. Can affect venting. |
How it is installed
A licensed plumber cuts the basement floor, installs the valve in the main line, and leaves an access box for cleaning. The City of Markham usually requires a permit and an inspection.
Using your home during a backup
When the valve is closed, your own water has nowhere to go. Avoid running water, flushing toilets or doing laundry until the storm passes. Otherwise, you could flood your own basement.
From the van: The City of Markham has offered a subsidy for backwater valves installed with a permit. Check current program terms.
Maintenance
- Lift the inspection lid each spring and again in autumn.
- Push the flap gently to confirm it swings without sticking.
- Remove any debris.
- Replace the cover securely.