What is a floor drain backwater valve?

A floor drain backwater valve is an important plumbing fixture that helps prevent sewage backups into a building. It is installed on the main sewer line leading from the building to the municipal sewer system or septic tank. The backwater valve sits between the floor drain and the main sewer line. It remains open to allow waste water to exit the building under normal conditions, but closes shut if sewage attempts to back up from the main sewer line into the building.

What is the Purpose of a Floor Drain Backwater Valve?

The purpose of a floor drain backwater valve is to stop sewage and wastewater from backing up into a building through the floor drain during a main sewer line blockage or municipal sewer overflow. Sewage backups can happen when there is too much rainwater infiltrating the municipal sewer system or a blockage occurs in the main sewer line. This causes wastewater to back up through connected pipes and floor drains. Installing a backwater valve on floor drains prevents this sewage backup by closing off the drain.

Preventing Sewage Backups

Backwater valves provide an important last line of defense to keep sewage contained in the sewer system and out of buildings. Raw sewage contains bacteria, viruses, and parasites that can cause serious health risks if humans come into contact with it. Backed up sewage can also cause terrible odors, flooding, and massive water damage within a building. A properly installed backwater valve shuts if sewage backs up toward the floor drain, keeping the contaminated water out of bathrooms, basements, crawlspaces, and anywhere else served by that drain.

Protecting Property from Damage

Backwater valves also prevent costly property damage by stopping sewage backups. Raw sewage can rapidly flood rooms, causing warped floors, mold growth, corroded appliances, and damage to walls, furniture, and other possessions. Sewage remediation costs thousands of dollars and often requires extensive repairs and replacements. A backwater valve installation provides relatively inexpensive peace of mind that the building is protected from these damages.

How Does a Floor Drain Backwater Valve Work?

A floor drain backwater valve works by using a mechanism that closes off water flow through the drain pipe when it detects a reversal in the normal direction of flow. Under normal conditions, wastewater flows down through the drain and into the main sewer line. The valve remains open to allow this downward flow.

During a sewer backup, water attempts to flow back up from the sewer line toward the building’s drain pipes. When the backwater valve detects this reverse flow, it triggers the valve mechanism to instantly close off the drain. With the valve closed, sewage cannot enter the property through that floor drain.

Backwater Valve Designs

There are two main designs for backwater valves:

• Flap valve: Uses a hinged flap that remains open for downward flow. If flow reverses, water pushes the flap closed across the pipe opening.
• Gate valve: Uses a sliding gate attached to a spring. The gate slides open for normal flow. Reverse flow pushes the gate shut against the spring tension.

Both designs provide an effective barrier against backflow when installed properly. The gate style valve generally requires less maintenance because it has fewer moving parts. Flap valves can become jammed open if too much debris builds up around the hinge.

Automatic Operation

Backwater valves are entirely self-operating and require no manual activation. As soon as reverse wastewater flow occurs, the change in water pressure triggers the valve to slam shut automatically. This prevents sewage backup through the floor drain. Once the blockage clears and normal downstream flow resumes, the backwater valve will reopen on its own to allow the drain to operate normally again.

Where Are Floor Drain Backwater Valves Installed?

Floor drain backwater valves are installed on the sewer lateral pipe that connects a building’s floor drainage system to the main sewer line or septic system. They are commonly installed in these locations:

• Basement floor drains
• Garage floor drains
• Laundry room floor drains
• Bathroom floor drains
• Crawlspace access point drains
• Any other interior floor drain connected to the sewer

Backwater valves should be installed on any floor drain that is at risk of sewage backup during a main sewer line blockage. The lowest level drains have the greatest risk. Drainage fixtures on upper floors may not need protection in single story buildings.

Existing Home Retrofits

Many homeowners have backwater valves added to their existing floor drains as a retrofit project. This is inexpensive sewage backup prevention for older homes. Building codes often require backwater valves when renovating basements or making plumbing alterations.

New Construction Installations

Backwater valves are commonly installed on floor drains during new home construction. Many current building codes require them, especially in flood zones. Installing them during initial plumbing work is easier and cheaper than retrofitting them later.

Backwater Valve Code Requirements

Many municipal building codes and plumbing codes now require backwater valves to be installed on floor drains connected to the sewer. Common code requirements include:

• Required on all basement floor drains
• Required on the lowest level floor drains for slab foundations
• Required within 2 feet of exterior access points like crawlspace drains
• Required on all drains located below the elevation of the next upstream manhole

Your local city or county building department will have details on specific backwater valve requirements for your area. Permits are usually required for installation.

Flood Zone Requirements

Areas designated as flood zones often have special backwater valve requirements. Floor drain valves may be mandated for all levels of the building, not just the lowest floors. This helps prevent sewer backups during heavy rains when municipal sewer systems are overwhelmed.

Septic System Requirements

Backwater valves are not usually required on septic systems. But they can still help prevent sewage backups from occurring if the drain field becomes saturated after heavy rains.

Types of Backwater Valves for Floor Drains

Several types of backwater valves can provide sewage backup protection for floor drains:

Inline Backwater Valves

• Installed directly on sewer lateral pipes
• Best for new construction and remodels
• Require cutting the pipe to install
• Flap valve or gate valve designs

Fixture Outlet Backwater Valves

• Install on or near floor drain body
• Easier retrofit for existing drains
• Use flexible couplings – no pipe cutting
• Only flap valve designs

Exterior Backwater Valves

• Install outside on sewer lateral
• Protects entire building’s drainage system
• Requires excavation to install
• Gate or flap designs available

An exterior backwater valve may be required forprotection of the entire drainage system. Interior valves just protect individual drains.

How to Install a Floor Drain Backwater Valve

Proper installation is crucial for a backwater valve to function effectively. Follow these steps:

1. Choose an approved backwater valve type and size it appropriately for the drain pipe size.
2. Position the valve in the correct location – must be downstream of the floor drain.
3. Inline valves require cutting the drain pipe. Maintain proper slope.
4. Fixture outlet valves use flexible couplings. Keep the valve upright.
5. Make watertight connections and secure all fittings.
6. Inline gate valves should be installed in a valve box for access.
7. Test valve operation by running water and checking that the valve seals properly against backflow.

Hiring a professional plumber is highly recommended, especially for inline valve installations. They have the skills and tools to install the valve correctly.

Maintenance Access

The backwater valve must remain accessible for maintenance and inspection. Inline gate valves should have an access box installed over them. Fixture outlet flap valves need clearance to open fully when backflow occurs.

Sewage Ejector Pumps

Homes with sewage ejector pumps may require a backwater valve installed on the ejector pump discharge line instead of the floor drain itself. This protects against pressurized backup from the sewer system.

Cost to Install a Backwater Valve on a Floor Drain

The cost to install a backwater valve on a floor drain averages $350 to $1000, with most homeowners paying $500 to $750. Here are the factors that influence the installation cost:

• Valve type – Inline valves cost more to install than fixture outlet valves.
• Drain size and location – Easily accessed drains cost less.
• Existing plumbing – Complex retrofits cost more than new construction.
• Excavation – Outdoor installations cost $1,000 or more if digging is required.
• Plumber’s rates – Prices vary based on location and experience.

Get estimates from several local plumbers before choosing one to install your backwater valve.

Valve and Equipment Cost

The backwater valve itself ranges from $50 to $300 depending on the size and type needed. Inline and exterior valves are more expensive. Additional parts like couplings, pipe, and access boxes will add $50 to $200 in materials.

Labor Costs

Expect to pay $200 to $800 in plumber’s labor for the installation. Simple retrofits of fixture outlet flap valves can cost as little as $200 in labor. Complicated inline gate valve installations with excavation often cost $500 to $800 for the work.

Do It Yourself Installation

Homeowners may want to tackle backwater valve installation as a DIY project to save on plumber costs. This can work well for simpler fixture outlet valves. But inline valves require advanced skills. Consider DIY under these circumstances:

• Good DIY plumbing skills and ability to follow instructions
• Fixture outlet valve type only
• Easily accessed floor drain location
• No required pipe cutting or excavation
• Willingness to take your time and do it right

otherwise, you are better off hiring a professional plumber for this critical sewage backup prevention system.

Hiring a Plumber

It is highly advisable to hire an experienced professional plumber for backwater valve installation in most cases. Here are some tips when hiring a plumber:

• Find a licensed, bonded, and insured plumber.
• Look for extensive experience with sewer and drainage systems.
• Ask about their backwater valve installation experience.
• Get at least 3 project quotes to compare.
• Check reviews and references.
• Avoid paying 100% upfront.

Having a qualified plumber install the backwater valve properly ensures it will work right when needed. Trying to save a little money on a DIY job could risk thousands in flood damages later.

How to Maintain a Backwater Valve on a Floor Drain

Like any valve, backwater valves need periodic inspection and maintenance to keep them working properly. This preventive maintenance helps avoid failure during a sewer backup event. Follow these backwater valve maintenance tips:

• Visually inspect valves annually in clean, dry conditions.
• Check flap valves for any debris, mineral buildup, or corrosion.
• Clean flap valves can be sprayed with lubricant.
• Ensure flaps move freely through their full range of motion.
• Inline gate valves should be fully opened and closed to keep them operating smoothly.
• Repair or replace any backwater valve that is not functioning properly.

Annual inspection and cleaning takes just a few minutes. This minor maintenance can prevent a valve failure leading to a disastrous sewer backup flooding event. Consider having your plumber add backwater valve maintenance when they service other plumbing each year.

Signs Your Backwater Valve Needs Replacement

Backwater valves normally last 5 to 10 years before needing replacement. Check for these signs that indicate it’s time for a new valve:

• Extreme corrosion and mineral buildup
• Cracked or warped body
• Missing or broken internal parts
• Flap is warped or has holes
• Gate is very hard to open or close
• Water leaks past the closed valve
• Valve is older than 10 years

Catching a failing backwater valve early and replacing it can prevent it from getting stuck open during a sewer backup. It’s smart to be proactive if you notice any issues during inspections.

Why Trust a Backwater Valve Over a Plug?

Some homeowners think they can simply insert an expandable rubber plug into floor drains instead of installing a true backwater valve. Here are the disadvantages of plugs:

• Easy to forget or fail to insert in time
• Can pop out under pressure
• Allow seepage past the seal
• Must be removed to use drain again
• No protection if you’re away

Backwater valves cost about the same as a good plug but remain in place to provide automatic, reliable backup prevention without any manual intervention required.

Conclusion

Installing backwater valves on your home’s floor drains provides critical protection against sewage and flooding damage. A few hundred dollars now can save many thousands of dollars in repairs and replacements if a backup occurs. Contact a professional plumber to have suitable backwater valves installed on your at-risk floor drains per code requirements. Then be diligent about having the valves inspected and serviced annually to ensure they function properly for long-term defense against sewer backups.