During sudden, heavy rains, city sewer lines can be overwhelmed. When that happens, water and/or sewage can flow back to your home—a nasty problem that leads to costly repairs and potential health risks.
A backwater valve is a simple device that can keep your home dry and safe from sewage backups. Keep reading to learn whether you need a backwater valve in your plumbing system.
What is a Backwater Valve and What Does it Do?
A backwater valve—also known as backflow and/or sewer backup valve—is a device installed on your sewer pipes that allows sewage to flow out to the public sewer and prevents sewage from backing up into your home.
Without a properly functioning backwater valve, sewage could come into the basement through a floor drains, sinks, tubs, and toilets.
Having a backwater valve installation on your sewer line is like having a strong line of defense, as it lets sewage flow one way and one way only—out of your home.
Here’s how a backwater valve works:
- Inside the valve is a small flap that’s normally open,allowing water to leave your home and sewer gases to vent.
- There’s a small floatation device on each side of the flap. If water or sewage starts to flow back into your house, the floaters raise and close the flap, stopping anything from entering your home.
- When water stops coming back toward your house, gravity drops the flap back into the open position, resuming the flow of water and sewage out of your home.
- Since backwater valves are usually closed, they can also help keep odor from a low-flowing city main line that becomes septic from getting inside your home.
- The top of the valve is usually clear so you see whether it’s working. There’s also a lid you can remove for cleaning.
Does My House Need a Backwater Valve?
First, see if you can determine whether your home already has a backwater valve. You’ll need to look for an access cover along your sewer line as it leaves your home. A plumber can help you with that.
If you don’t have a backwater valve:
- Try to determine the elevation of the lowest drain in your home and compare it to the height of the manhole cover for the public sewer upstream of your sewer connection.
- If your drain is lower than the manhole cover, you’ll need a backwater valve installation.
In addition, some municipalities require backwater valve installation, while others simply make it a recommendation. One thing’s for sure—there’s a greater risk of a sewer backup if your home has:
- A basement.
- A ground floor that’s less than a foot above street level.
The National Plumbing Code1 requires newer homes with plumbing fixtures below street level to have backwater valves. If you live in a part of the country with sudden and heavy rains, it’s worth looking into having backwater valve installation in your plumbing system.
How Much Does a Backwater Valve Installation Cost?
The sewer backwater valve installation cost depends on whether you’re building a new home or retrofitting an older home.
- Backwater valve cost for newly built home is usually no more than $2002 (depending on where you live), since backwater plumbing can easily be added to the rest of the home’s plumbing system.
- Retrofitting an existing plumbing system takes the backwater valve installation cost up to $1,100+3. A plumber will have to cut a hole in the concrete floor, usually near the floor drain. The plumber will dig down to the main sewer line, cut out a portion, and replace it with the backwater valve.
When you retrofit a backwater valve, you also need a plumbing permit from your municipality. Some municipalities offer subsidies to help cover the cost of backwater valve installation.
Backwater valve installation can reduce your homeowner’s insurance costs4, so don’t forget to let your insurance provider know if you install backwater plumbing.
Do You Need to Install a Backwater Valve?
Nobody wants wastewater flowing into their home. And unless your house already has a backwater valve attached to the sewer line, installing one of these devices is a simple—if somewhat costly—precaution you really can’t afford to do without.
