How to Install a French Drain

Figure out where the excess water is pooling and where you want it to go.

• When choosing an outlet for runoff water, look for retention ponds or other bodies of water. Or you can tap into existing drainage. You can also divert the runoff water to the road curbside, if that's easiest.
• Do not drain onto a neighbor's property.
• Use striping spray paint, stakes, flags or another method to mark the trench's direction and length.
• For proper drainage, the trench and pipe system should always drain from a higher elevation and let out water at a lower elevation.
• Always direct the water away from your home.
• Before the French drain installation, make sure your neighborhood has no zoning restrictions and get necessary permissions.

Tip: Confirm that your water issue is not caused by leakage from underground pipes that need repair.

Dig a trench from the place in your yard that needs drainage to your chosen outlet.

• Check for underground utility lines and pipes before digging.
• The trench should be about 18 inches deep and 9-12 inches wide.
• French drains need to have a slope of at least 1 percent, so the force of gravity will work for you. This means that the drain should slope down a total of at least one inch for every 10 feet of pipe.

Depending on your trench's size, you can dig with shovels and other hand tools. Or you may consider a trencher, a machine that quickly makes even, straight trenches. Typically, their holes are smooth at the sides, flat at the bottom and deeper than they are wide. Trenchers are recommended over shovels for holes more than 100 feet long. They're also preferred for use in dense, rocky terrain.

Safety Tip: Call 811 a few days before starting any outdoor digging project. A nationwide practice, it alerts utility companies about excavation plans. Locators will paint the ground or plant flags at your site. This marks and prevents accidental damage to underground line locations, including electric, water, gas and cable.

• Lay water-permeable filter fabric or a weed barrier over the gravel bedding in the trench. This keeps the French drain free of dirt, silt and tree roots.
• Leave the filter fabric open with at least 10 inches of excess fabric at the sides.

Pour and compact about 3 inches of gravel or landscaping stone along the bottom of the trench. This will act as bedding for the drainage piping.

• Install an inlet grate at the point where the water pools the most.
• Secure as many fittings as necessary for your pipe system to extend from the inlet grate to the water outlet point.
• You can use an inexpensive, flexible drainage hose if you need a curved drain. Or, for a more durable system, use longer-lasting PVC pipe. If you choose the latter, drill holes about 6 inches apart along the length of the pipe.

• Lay the connected pipe structure in the trench on top of the layer of crushed stone. Make sure the drainage holes in the perforated pipe are pointed downward.
• Test the flow of the drain by pouring water into the inlet grate.

• Cover the pipe with about 3 inches of gravel or crushed stone, but not enough to cross above ground level.
• Wrap the excess filter fabric over it for another layer of protection.

• Fill the trench with topsoil and compact to completely cover the entire French drain system.
• When filling the area around the inlet grate, temporarily cover the grate to prevent any stones or soil from falling in after installing the French drain.

• Reseed the surface if necessary or cover with landscaping stone.
• Regularly inspect and clean the inlet grate and outlet point.
• Flush debris when needed to keep the water flowing freely.
• If your French drain breaks or gets clogged, you may have to dig up part of it for inspection or repair. This is easier if it’s covered with landscaping stone and not grass.

Looking to save some steps in the process of French drain installation? Consider purchasing an alternative gravel-free drainage pipe system. This system uses a corrugated pipe surrounded by polystyrene aggregate that is then wrapped in filter fabric.

If you choose this approach instead of manually building a French drain, skip the filter fabric and crushed stones steps listed above. Just place the product in the trench following the manufacturer's instructions and cover with soil.

Whether a French drain trench or another digging project, you may choose to rent a trencher. The Home Depot Rental has a large selection of trencher rentals. Before renting, you should estimate future trenches' length, width and depth.

• Walk-behind trenchers are pulled from behind, with users walking backwards, rather than pushing. Easy to maneuver, with user-friendly controls, they work better with softer terrain or more precise needs.
• Ride-on trenchers are motorized and ridden. They’re designed for long, deep trenches, rocky terrain or pavement.
• Chain trenchers have chains or digging belts, like chainsaws. They can cut deep, narrow trenches well-suited for drainage.
• Wheel trenchers have metal wheels with teeth (rockwheels). They can handle rocky soil, pavement or concrete, as well as softer soil.
• Excavators, a type of heavy equipment, dig ditches wider at the top than the bottom. Able to dig to greater depths than trenchers, they work with all terrains.