What Is a French Drain? Find Out If One Is Right for Your Yard

Additionally, a French drain must be able to take the water to a location where it no longer poses a threat. This can be a storm drain, retention pond, or simply a safe spot away from your home.

What Is a French Drain?

Move standing water away from your yard by installing a French drain system.

Timothy Dale is a home repair expert and writer with over a decade of hands-on construction and home improvement experience. He is skilled in residential, commercial, industrial and institutional plumbing, electrical, carpentry, installation, renovations, and project management.

Richard Epstein is a licensed master plumber with over 40 years experience in residential and commercial plumbing. He specializes in estimating as well as design and engineering for plumbing systems, and he works for one of New York’s largest union plumbing construction companies.

Heavy rain and melting snow can lead to water accumulating in the yard, where it forms puddles and creates large areas of mud and standing water. In addition, when the water cannot drain away from the yard, it may flow towards the home, resulting in flooding and water damage. To help protect the foundation of the home from ongoing damage and to prevent flooding, a French drain can be installed to redirect the flow of water away from the home. By drawing water in from the saturated ground, the French drain system also reduces standing water in the yard, so your kids and pets can enjoy the lawn without worrying about huge puddles.

So, what is a French drain, and how does it work? Basically, a French drain is a simple trench dug in the ground in the most problematic areas of the yard. The trench is filled with a perforated pipe wrapped in water-permeable fabric, and the pipe is covered with several layers of stone or gravel. French drain systems work because gravity causes the water to flow downhill, and water will always follow the path of least resistance, so it is naturally drawn down through the stones into the hollow pipe where the water can flow freely on a downward slope towards a municipal drain, a rain barrel, or any other suitable location for water drainage.

French Drain Systems

The French drain was detailed in an 1859 book written by Henry French, a judge and farmer who lived in Concord, Massachusetts. He helped to popularize the idea specifically to drain excess water away from crop fields in order to improve the crop yield and prevent flooding. The system was named for Henry French and has been used since his time to improve crop field drainage, reduce yard saturation, and help protect housing foundations.

It’s a basic design that takes advantage of scientific laws to quickly and effectively drain excess water away from a given location. Gravity acts on the water to draw it down into the soil, but the water will always take the path of least resistance, so you can install a French drain, which creates an ideal path for the water to take through a hollow, perforated pipe under several layers of stone or gravel.

For instance, during a heavy rainstorm, water can accumulate around the foundation of the home and eventually seep into the basement because it doesn’t have a drainage path. However, installing a French drain around the foundation helps to pull water away from the home and into the hollow drainage pipe, making use of water’s tendency to follow the path of least resistance.

How French Drains Work

The basic principle of a French drain is to provide a path of least resistance for water to follow instead of building up and flooding the soil. This is achieved with a hollow, perforated drainage pipe that can collect and carry the water from the yard to a designated drainage location, like a municipal wastewater drain or a rain bucket. The drainage pipe is wrapped in water-permeable fabric to prevent weeds, dirt, and other debris from obstructing the perforations in the pipe. Additionally, the pipe is covered in several layers of stones or gravel. By replacing soil with stones or gravel, you help the water flow down into the drainage pipe because it’s much easier for water to move through the larger gaps provided by packed stone than it is for the water to flow through densely packed soil.

Each aspect of a French drain is designed to make it easier for the water to move down from the surface, through the stones, through the unobstructed perforations, into the hollow drainage pipe. The drainage pipe should be set at an angle so that when the water enters the pipe it immediately begins flowing away from the home to prevent water build-up and flooding.

Just keep in mind that if you do not use a water-permeable fabric to wrap the drainage pipe, the water cannot enter the drainage pipe, so the flooding issues will continue. Every material used in the installation needs to improve the flow of the water, otherwise, the French drain becomes ineffective.

When to Use French Drain Systems

Before deciding to start trenching the yard, it’s important to understand when a French drain system is beneficial and how it can help to improve common problems caused by heavy rain, excess groundwater, and melting ice or snow.

Recurring Flooding and Foundation Damage

A weeping tile or interior French drain can be used to protect the basement from recurring floods and to prevent further damage to the foundation. Weeping tiles are a type of exterior French drain that can be installed around the perimeter of the home to draw water away from the foundation. This reduces the hydrostatic pressure on the foundation, giving the water an alternate path to follow instead of being forced through cracks in the foundation wall.

What Is Weeping Tile?

Weeping tile is a term that is often used when discussing French drain systems. This is because weeping tile is a type of French drain that is specifically used to protect a structure against hydrostatic pressure. This means that weeping tile is typically installed at a deeper point than a standard French drain for the purpose of preventing flooding and damage to the foundation of the home.

However, if the water is already seeping through the foundation and into the home, it may be better to invest in an interior French drain. These systems typically consist of a drainage board that sits between the foundation wall and the interior wall of the home. The drainage board collects any water that seeps through cracks in the foundation and redirects it to a French drain buried under the concrete floor of the home.

Pooling Surface Water

One of the most common uses of a French drain is to draw in water that has formed puddles or large pools on the surface. The drain pulls in water from the saturated soil by providing an easy path for the water to follow. It’s then redirected to a more suitable drainage location, like a municipal wastewater drain. You can also direct the water to a catch basin, like a rain barrel, so the collected water can be used during the warmer months of the year to water the garden or lawn.

Retaining Walls Under Pressure

Retaining walls help to hold soil in place and prevent erosion, but when the soil becomes overly saturated, this can exert increased pressure on the retaining walls, causing them to fail. Installing a French drain to help draw in excess water and redirect the flow away from the retaining wall is a great way to help protect the integrity of the structure during heavy rainfall.

Cost of Installing a French Drain

Another factor to keep in mind before installing a French drain is the cost of materials, as well as any costs associated with hiring a professional to complete this work. While this task can be handled by an experienced DIYer, many people may prefer to have the system professionally installed to ensure that it will work effectively. Additionally, hiring a professional can give you better peace of mind because most companies will guarantee their work, so if there are any problems with the French drain or if any other electrical or plumbing lines are damaged during the installation, you can contact the company to resolve the issue.

The average cost to have a French drain professionally installed is about $5,000, though it can climb to $18,000 for an interior French drain installation. Keep in mind that the longer the drainage trench, the higher the cost of materials. In general, you can expect to pay about $10 to $50 per linear foot for an exterior French drain and about $40 to $100 per linear foot for an interior French drain due to the specialized membranes and additional work required to install this type of system.

What Is a French Drain? Find Out If One Is Right for Your Yard

Learn how this drainage solution could save you thousands in home repairs.

In a perfect world, every home would be situated on top of a hill. This way, all the rain and snow melt would effortlessly drain away from the home along with all the worries of water damage, flooded basements, foundation issues, and mud-covered lawns. Unfortunately, this isn’t the case for most homes, leaving homeowners in search of an alternative drainage solution. Enter the French drain.

Despite their name, French drains aren’t actually from France. In fact, they’re named for a Massachusetts judge and farmer, Henry French, who first wrote about them in 1859. The idea was simple: Get water away from the places it tends to collect by carving out an easy path for it. However, unlike a ditch, this drainage path is totally underground.

What is a French Drain?

A French drain is a trench that houses a perforated pipe buried beneath layers of gravel. When water pools on the ground above, gravity pulls it through the gravel and into the pipe, where it drains out the end.

How a French Drain Works

Water will always follow the path of least resistance. While a steep hill is the ideal solution for draining water, flatter areas pose drainage problems. French drains circumvent these issues by creating a path that transfers the water to a spot where it no longer poses a problem, such as a storm drain or rainwater collection system.

The French drain works by encouraging groundwater to seep into the drain with layers of gravel. Water travels through gravel much more efficiently than soil, so once water soaks into the soil, it quickly enters the pipe. A permeable fabric prevents the gravel or other foreign objects from entering the pipe, leaving it free of debris and ensuring maximum drainage potential.

Requirements for a French Drain

The most crucial requirement for a French drain is the slope. If you’re unable to install the French drain with at least a 1% grade drop (a 1-inch drop over 10 feet), the drain will not function as intended. Installing a French drain without enough slope will result in standing water in the drain and improper drainage.

Additionally, a French drain must be able to take the water to a location where it no longer poses a threat. This can be a storm drain, retention pond, or simply a safe spot away from your home.

When to Consider Installing a French Drain

Think a French drain might be the right solution for your water woes? Here are a few common problems that can be solved with a French drain.

1. Foundation Damage Due to Poor Drainage

If your home experiences flooding or foundational damage due to groundwater, rain, or snowmelt, a French drain may take care of the problem for good. A properly installed exterior French drain will completely circle your home’s foundation, exiting at the lowest point to drain the water away from the home. To do this, the entire drain must be installed at an angle that promotes drainage. This type of French drain is often called a weeping tile system and is intended to relieve hydrostatic pressure on the walls of the foundation.

If water has become an interior issue, it might be more beneficial to install an interior weeping tile. This entails installing a moisture barrier called a drainage board along the outer walls to deflect water into a French drain that circles the entire interior circumference of the foundation. The drain then redirects the water out of the home via an exterior drain or sump pump.

2. Hydrostatic Pressure on Retaining Walls

Like foundation walls, retaining walls can be compromised by hydrostatic pressure. A French drain installed on the upper side of a retaining wall and routed to drain away from the wall will pull water out of the ground and remove hydrostatic pressure.

3. Flooding or Excess Surface Water

Does your lawn or garden hold an excessive amount of surface water after wet weather? Installing a French drain might be what it takes to reclaim your lawn. While French drains are designed to remove groundwater along the pipe via perforations, you can install drains in the ground anywhere water tends to collect. This way, the drains immediately remove any water before it has a chance to enter the ground, as well as any water that’s already in the ground.

How Much Does a French Drain Cost?

French drain installations are very labor intensive, which can add up to high costs if you choose not to do the labor yourself. Even if you do opt to do the job yourself, keep in mind that the materials are not cheap. A 10-foot section of perforated corrugated pipe with aggregate and mesh fabric will cost around $80. If you choose to rent digging equipment to save your back, you can expect to pay around $300/day for a 1-ton mini excavator.

Many homeowners opt to hire professionals to ensure the installed French drain operates as intended. Additionally, a professional will have the tools and know-how required to tie the drain into a municipal storm drain, should it be necessary. For professional exterior French drain installation, you should plan on paying around $5,000, though this number will vary depending on your drainage requirements. Interior weeping tile installations are much pricier, falling between $10,000 and $20,000.

Frequently Asked Questions

As long as they’re installed properly where there’s enough of a slope, French drains work very well, and can last for many years.

What drainage solution is better than a French drain?

For some homeowners, a sump pump is better than a French drain. Other choices are concrete stairs which add architectural interest to deep slopes as they direct water to a drain, or a drainage swale in your landscape to move water away from your home.

How is a French drain different than a regular drain?

A French drain captures and removes water below the ground, while trench drains remove surface water.

French drains should be cleaned out at least once a year or more if needed. The easiest way to clean them is with a pressure washer. If your drain still seems clogged, use a snake made for heavy-duty clogs. It’s a good idea to check the French drain when you clean it for any cracks or separations in the pipes.