What Are French Drains?

French drains are a simple system of providing drainage for homes, septic tanks and areas that need protection from minor flooding. This type of drainage system was popularized by Henry French in the 1800's. The systems are also called perimeter drains, land drains, rubble drains or drain tile.

Purpose:

French drains are used to move ground or surface water from one area to another. They can be as simple as trenches dug in the ground and covered by rock and gravel or more elaborate systems of perforated piping. They can prevent a build of water around foundations and help relieve water pressure on retaining walls. French drains have grown over the years from gravel trenches to tile and pipe systems to more elaborate PVC assemblies with valves and clean outs.

Exterior French drains:

French drains or gravel systems are commonly used on the exterior of foundation walls when a home is being built. Trenches will be left around the footer and filled with gravel or tile before soil is placed for backfill. A protective fabric membrane should be used over the gravel to keep sand and dirt from clogging the system. Perforated pipe may also be used and may be clay or PVC. Pipes will also be subject to clogs from sediment and should be covered as well.

Interior French drains:

French drain systems may also be found along the interior walls of a basement. These can be installed when the home is built or done afterwards as a solution to a wet basement problem. A trench will be placed at the base of the basement walls to drain water that enters the area. Interior systems should direct the water to a sump pump as the best means for removing the water from the home. Without a sump pump the water will remain standing creating more problems. For basements that only have occasional problems, with small amounts of water entering at the wall base, a French drain should provide all the assistance that is needed.

French drain systems are not the most reliable method for preventing flood damage. They can clog easily and clay tile can deteriorate over time. When used as an additional method to relieve water pressure and drain water away from foundations they can be effective. In areas that are prone to heavy rain and flooding they should not be relied on without the use of a sump pump.