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Basement protection

Backwater valve installation and replacement

A backwater valve stops water from the municipal sewer from rising into your basement when the system overflows during a heavy storm or the spring thaw. Our plumbers install and replace them in houses and plexes: they first check how your drains are connected, then fit the right valve in the right place, with clear access for maintenance. The price is confirmed before the plumber heads out, with no obligation.

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A plumber answers day and night · RBQ licence 5881-1431-01 · CMMTQ member · Insured

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Plumber lifting the access cover of a valve set in a basement floor

Why trust us to protect your basement

A valve in the wrong spot leaves outlets unprotected, and one nobody can open cannot be maintained. Here is how we avoid both.

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  • Your connections checked first

    The plumber traces where every basement fixture connects before choosing the location, so every outlet is protected without slowing normal drainage.

  • Planned around the RénoPlex subsidy

    Mention the RénoPlex subsidy when you call and we will schedule the installation accordingly.

  • Our own plumbers

    The valve is installed by a plumber from our team, never by a subcontractor.

  • No diagnostic fee, guaranteed in writing

    The price is set on the phone before the plumber is sent, with no service-call fee. The installation is covered by a written warranty; if the same problem comes back during the warranty period, a technician returns at no extra charge.

A plumber answers day and night

Talk to a plumber

(438) 379-2352
  • Price confirmed before we head out
  • Someone on our team answers right away
  • RBQ licence 5881-1431-01
  • 5.0 out of 5 · 121 Google reviews

What does a backwater valve do?

It lets wastewater flow from the house to the municipal sewer, and closes as soon as water tries to go the other way. Without one, when the public system overflows, sewer water rises to the lowest point in the building: the floor drain, the shower or the basement toilet.

Inside, a small flap swings freely while water drains normally. When the level rises in the street sewer, the pressure pushes the flap against its seat and closes the passage. It’s simple, but it only works if the flap moves freely and nothing keeps it from closing: a stuck piece of debris, buildup or a worn part is enough to let water through.

The valve only protects the outlets it is installed on. A fixture connected downstream, or a forgotten outlet, stays open to backups. That’s why the location matters as much as the device itself.

What the City of Montréal requires

In Montréal, the By-law concerning the protection of buildings against sewer back-up (11-010) makes the valve mandatory, and since 2011 it must be installed in all new buildings. The City specifies that it goes on the drain pipe of each basement fixture or group of fixtures: toilets, washbasins, shower stalls, washing machines, garage floor drains. It must also stay easy to reach for maintenance.

After a sewer backup, the City’s liability is not automatic if you did not have a valve in good working order. A missing, blocked or inaccessible valve can therefore hurt your claim against the City.

Elsewhere in the region, each municipality has its own requirements. Before any work, check your city’s by-law; the plumber can tell you what they see in your home.

Signs of a worn, blocked or badly placed valve

The City of Montréal points out several problems: devices installed in the wrong place, worn out to the point of failing, chewed by rats, or hidden under flooring laid afterwards. At home, these signs should get your attention:

  • water has already come up through a basement floor drain, shower or toilet, even briefly;
  • a sewer smell lingers in the basement even though the traps are full of water;
  • the access cover can’t be found, is sealed, or sits under flooring or built-in furniture;
  • the flap no longer moves when you open the cover, or buildup collects around it;
  • nobody has opened it in years, or you don’t know whether you have one;
  • a fixture was added in the basement, such as a shower or a washing machine, without reviewing the protection.

How our plumbers install a backwater valve

Every installation follows the same steps, whether it’s a first valve or the replacement of an old one.

  1. A price before we leave. On the phone, we ask the right questions about the basement and its fixtures, and the price is set before the plumber is sent.
  2. Connections checked. The plumber traces where each basement fixture connects and picks the location that protects every outlet without slowing drainage.
  3. Installed with clear access. The valve goes on the right pipe, with a cover you can open without special tools or demolition.
  4. Tested and explained. The plumber checks the drainage, shows you how to open the cover and what to look at during maintenance. You pay once the work is done, and the installation is covered by a written warranty.

How much does it cost to install a valve?

The price mainly depends on access to the pipe, the number of outlets to protect and the floor that has to be opened. A valve installed on a visible pipe takes far less work than one that has to go under a concrete slab. On the phone, we ask the right questions and the price is confirmed before the plumber heads out.

  • Price set before the plumber is sent, with no hidden fees.
  • No obligation on your part.
  • You pay once the work is done.
  • Written warranty on labour and parts.
Get my price by phone · (438) 379-2352

Montreal’s RénoPlex subsidy for your valve

In Montréal, the City’s RénoPlex program helps owners of buildings with 1 to 5 dwellings with renovations, including flood protection. The City’s current schedule provides $90 for installing a normally closed valve, and $600 per valve installed under an existing slab.

One condition is essential: you must wait for confirmation that your application is approved before starting the work, or you risk losing the subsidy. The other conditions, such as the value of the building, are set out on the program page. If you plan to apply, tell us when you call so we can schedule the job accordingly.

Maintain your backwater valve twice a year

The City recommends checking, ideally twice a year, that the valve works and is not blocked. Spring, before the snow melts, and late summer, before the fall storms, are good times.

  • Open the access cover following the manufacturer’s instructions, wearing gloves.
  • Look at the flap: it should move freely and close completely.
  • Remove debris and buildup around the seat, without forcing the part.
  • Close the cover tightly so it stays watertight.
  • Keep the access clear: no furniture or flooring on top.

If the flap is cracked, warped or no longer closes, have it replaced before the next heavy rain. If water is already in the basement, see our page on sewer backups for what to do in the first hour. Water seeping in through the foundation walls comes from somewhere else, such as a clogged foundation drain or a crack: a valve won’t stop it.

Sources

Our process

The price is confirmed on the phone before the plumber heads out, and the work is guaranteed in writing.

  1. Step 1

    You call

    We listen to what happened and how serious it is. The price is set on that call, before a plumber is sent. No obligation, and no hidden fees.

  2. Step 2

    We head out

    An RBQ-licensed plumber who is a CMMTQ member leaves for your address. The truck is stocked for the job, so the visit can be handled the first time.

  3. Step 3

    Fixed, and guaranteed

    The work follows RBQ standards. You pay once the problem is resolved, and you leave with a written guarantee on labour and parts.

No-obligation quote

Get your price before we head out

Tell us what you need in a few words. We call you back at the number you give to ask the right questions and confirm the price.

Want to add photos? Use the full form

  • The price is confirmed before we head out
  • No obligation on your part
  • RBQ-licensed company, CMMTQ member
5.0 out of 5 · 121 Google reviews Rating checked on October 14, 2026 Read the reviews on Google

An emergency? Don’t write, call: (438) 379-2352

What our clients say

5.0 out of 5 · 121 Google reviews Rating checked on October 14, 2026 Read the reviews on Google

  • “I had a wonderful experience with this plumber! He was extremely nice, kind, professional, and very respectful. He arrived quickly, worked efficiently, and fixed the issue much faster than I expected. I really appreciated his excellent service and positive attitude. I highly recommend him to anyone looking for a reliable and professional plumber. Thank you so much! 🙏”

    Lena O. · Google

  • “The guys were amazing! Came in quick, same day actually, even on a Sunday. They did a fab job and my sink is working better than ever. Thanks team! 🫶🏻”

    Clari S. · Google

  • “I highly recommend Plomberie Pipemasters. When I called, they arrived promptly and fixed the leak quickly. They were professional and left the area clean and in order.”

    Annabelle H. · Google

Common questions about backwater valves

(438) 379-2352
Is a backflow valve the same as a backwater valve?

Yes. Backwater valve, backflow valve and sewer backflow valve all describe the same device, a small flap installed in the drain pipe that lets wastewater out and closes when sewer water tries to come back in.

Normally closed or normally open backwater valve: what's the difference?

A normally closed valve stays shut at rest and only opens when water from your fixtures drains to the sewer. A normally open valve stays open at rest and only closes when sewer water comes back. The City of Montréal's RénoPlex schedule covers the normally closed type. The plumber checks how your drains are connected before recommending a type.

How many valves does a house need?

It depends on the connections. The City of Montréal asks for a valve on the drain pipe of each basement fixture or group of fixtures. Depending on how the toilet, shower, washing machine and floor drain are tied in, one valve may be enough or several may be needed. The plumber confirms it after seeing the installation.

My basement flooded even with a valve. Why?

The valve may have been blocked, worn or installed in the wrong place, or the water came through an outlet that was not protected. Sometimes the water comes from somewhere else entirely, such as seepage through the foundation. A plumber can check each outlet and tell you what let the water in.

Does the valve stop a clog in my own pipe?

No. It blocks water rising from the municipal sewer, not a clog in your own connection. If water backs up because your pipe is blocked, the pipe has to be cleared.

The floor covers my valve. Is that a problem?

Yes, because a valve nobody can open cannot be checked or cleaned. The City reminds owners that access must stay easy. The plumber can assess the best way to restore access or move the valve.

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