What Is a French Drain System?

A French drain can be used to remove water from low lying areas.

A French drain, also known as a drain tile, is a method of draining water from low lying areas. A low spot in a yard, for example, can be drained into a nearby ditch by force of gravity alone. French drains are also commonly used to drain water from around foundations of buildings and into a sump pit.

History

The French drain was invented by a Concord, Massachusetts farmer named Henry French. Described in his book "Farm Drainage," French drains were first used in the mid-1800s. French's original invention used roofing tile in a trench and covered with soil to drain water away from buildings.

Construction and Function

Modern French drains consist of a sloping trench filled with rock or gravel, allowing water to drain into the trench and occupy the space between the rock or gravel as it drains out the low end of the trench, without having an open trench. Most French drains include a perforated plastic pipe to allow water to move through the trench faster. A French drain installed around the foundation of a house, for example, uses pea-sized rock surrounding a perforated pipe to allow ground water to drain into a sump pit where it can be pumped outside and away from the house.

Advantages

A French drain is a relatively inexpensive and low maintenance method for removing water from an area. Used to drain a low area of a yard or park, the French drain can be covered with filter fabric, topsoil and grass so that the drain goes entirely unnoticed. A French drain is also one of the only reliable ways to drain water from around a building's foundation.

Disadvantages

The biggest threat to a French drain is clogging. Fine sediment can seep into the rock and pipe over time and reduce the drain's capacity or plug it entirely. Without access to the perforated pipe, this can be difficult if not impossible to fix. Badly plugged French drains usually need to be dug up and reconstructed, which can be quite expensive. Filter fabric is commonly used on top of the gravel and around the perforated pipe to prevent this, but the fabric itself can become clogged if fine sediment builds up around it.

Legal Considerations

While there is rarely an issue with a French drain used around a building's foundation, large scale french drains can introduce a legal issue. Draining water onto a neighbor's land, for example, or into a ditch or municipal storm drain may require a permit from local authorities. French drains are also used in the United States to drain farm land, and some of these wetlands may be protected by the federal government.

References

• Concord Magazine: What's So French About French Drains? And Other Musings on Concord Agriculture
• Ask The Builder: A Simple Trench Drain