DRAINAGE

French Drain Systems: When You Need Them

If you have a soggy yard or a wet basement, then a French drain is your cure. Here’s how they work, when to use them, the different types and cost.

Water always flows downhill, and by the easiest route possible. That’s the basic concept behind a French drain, a slightly sloped trench filled with round gravel and a pipe that diverts water away from your house.

By the way, the name doesn’t come from the country. It’s from Henry French, a judge and farmer in Concord, Mass., who promoted the idea in an 1859 book about farm drainage.

How a French Drain Works

French drains provide an easy channel for water to flow through. Water runs into a gravel-filled trench, then into perforated pipe at the bottom of the trench.

Water travels freely through the pipe, which empties a safe distance from the house.

The trench bottom should be sloped about one inch for every eight feet in the direction you want water to flow. Depending on your situation, the water can be diverted to:

• A low-lying area of your property
• A drainage ditch
• A dry well
• The street

When You Need a French Drain

• When you have a problem with surface water, such as a soggy lawn or a driveway that washes out
• If water is getting into your basement
• If you’re building a retaining wall on a hillside

If Your Problem is Surface Water

Install a shallow French drain. Also called a curtain drain, it extends horizontally across your property, directly uphill of the area you want to dry out. It intercepts water and channels it around the soggy spot.

This type of drain doesn’t have to be very deep. A common size is two feet deep and 1.5 feet across. Where the drain passes through areas with trees or shrubs, switch to solid pipe (not perforated) to reduce the risk of roots growing into the piping and clogging it.