How to Install a French Drain in Your Yard

Pools of water in the yard, seepage into the basement and excessive runoff from patios, walkways and driveways are all problems that can be solved by installing a French drain. This type of drain isn't really French, so you don't have to worry about ordering one from overseas, and it isn't exotic either. Named after its Massachusetts-based inventor, Henry French, who came up with the simple and useful idea in the mid-1800s, the French drain system was first popularized in his book Farm Drainage, available online at Project Gutenberg, and it has been a landscaping staple in North America and elsewhere since the book was published in 1859.

The concept of a French drain is simple, and any homeowner with a shovel can install one in the yard. It's basically a gravel-filled trench dug with a slight slope toward a catchment or runoff point. Inside the trench is a length of perforated drain pipe that is covered with landscape fabric to prevent clogging, and because the trench is ultimately covered with topsoil and possibly sod, it disappears. Some French drain systems, particularly those around foundations or in basements, do require professional installation, but a simple yard drainage system can easily be a DIY project.

In an ideal world, a property is graded away from the house with a slope gentle enough to allow rainwater to seep into well-draining ground, and where slopes do create streams, the streams flow harmlessly toward a natural catchment or runoff point. The world and its properties are seldom ideal, however, and any one of the following conditions can create drainage problems:

• Poorly draining soil
• Low spots and depressions
• Streams caused by abrupt changes in slope or man-made obstructions
• High water table and springs

A French drain system can improve drainage in any of these situations by collecting water at ground level and directing it to a suitable place. In an effort to conserve water and protect water quality, many communities place restrictions on directing water off the property. Where no natural runoff point exists or directing the water to a municipal drainage network is impractical or illegal, the drain pipe can terminate in a dry well on the property.

French drains can also resolve drainage problems around the foundation and in the basement. Footing drains catch water that would otherwise seep through the foundation walls, and channel drains covered by drain tile in the basement floor direct excess water to a central point where a sump pump can transfer it outside. Installation of footing and channel drains is usually a job for professional contractors because of the amount of digging involved and can cost from $50 to $100 per linear foot, according to data from Fixr.

It isn't difficult to tell where a French drain would be of most use in your yard. Just look for low-lying areas with standing water or soggy soil that stay that way for days after a heavy rain. These areas might have clay-like soil or be receiving water from areas of higher elevation that surround them, and they are perfect candidates for a French drain installation. Other likely places include the edges of impermeable surfaces, such as a concrete patio or asphalt driveway, where runoff is heavy and water pools.

Because a French drain is permeable, it absorbs water from the surfaces as well as from deep in the ground, and the water flows in the direction of the trench slope, which should be 1 inch for every 8 feet (a 1 percent grade) at a minimum, according to Mr. Rooter. A gentle slope allows some of the water to drip through the holes in the perforated drain pipe and sink into the soil, eventually returning to the water table.

Because the end of a French drain system has to be at a lower elevation than the beginning, it makes sense to install it on ground that follows a downward slope if at all possible. That way, you can keep the trench a uniform depth. When you can't avoid installing one on flat ground or ground that slopes in the opposite direction of the drain, you have to plan for extra depth at the end, and this can be considerable. For example, if you install a 100-foot drain on flat ground, the trench has to be more than 12 inches deeper at the end than it is at the beginning, so it's best to keep the drain as short as possible to limit the amount of digging you have to do.

Locating the exit of the drain also takes careful planning. According to Houselogic, the best exit is on a grassy slope with good sun exposure or on the street if allowed by your community. The drain should never direct water onto a neighboring property or anywhere it could cause erosion or cover sidewalks and public thoroughfares with water that could turn into ice. Once the drain has been installed, you can cover it with turf, soil or, if it suits the landscape design, tiles or gravel.

If your best option is to drain the water onto the street, be sure to check with the local planning office to determine whether you need a permit and what regulations apply. In cases where no suitable natural runoff point is available, the only other option is to terminate the drain in a dry well, which is a gravel-filled pit that holds water and allows it to percolate slowly into the ground. If the drain has to handle large amounts of water, it may be a good idea to dig several smaller dry wells along the course of the drain.