Drains & sewer
Why Basement Floor Drains Back Up
Updated · Kestrel editorial
Short answerThe basement floor drain is usually the lowest opening on the sewer line, so any blockage in the main shows up there first. Common causes are roots in clay pipe, grease, a sagging line, or the city main surcharging in heavy rain.
What to do now
Stop using water, keep people and pets away, and call to have the main cleared.
Finding the cause
A sewer camera inspection shows roots, breaks or bellies.
Prevention
- Backwater valve for city-side surcharges
- Routine root cutting or lining
- Keeping grease and wipes out of drains
Protecting a finished basement
A backwater valve on the main line stops city sewer water from flowing back into the house during a surcharge. Pair it with a camera inspection to rule out roots or a sagging line, and consider a sewer backup endorsement on your homeowners policy.
Why Basement Floor Drains Back Up: follow-up questions
Is floor drain backup a plumbing or city problem?
It depends where the blockage is. A camera shows whether it's in your private line or at the city main.
Can I plug my floor drain?
Not permanently; floor drains are required in many basements. A backwater valve or drain plug with a float is the safer option.
Every home differs; editorial standards.