Types of French Drains

Original French Drain Design

• The French drain was originally developed by Henry French, and popularized by his book in 1859. French improved upon existing drainage systems by eliminating the main problem with other drains: clogging. French added crushed rock to a channel to prevent it from clogging with debris. The rock acts as a natural filter, allowing the water to move through the channel, but preventing soil, leaves and other organic matter from clogging the water's path. This most basic design simply involved a dug trench, crushed rock and perhaps a layer of sand on top of the rock. The trench should be sloped to channel the water to whatever point has been designated to handle the water collection, be it a sump pit, a dry well or simply a more appropriate water accumulation point.

French Drain with Drainage Pipe

• Most modern French drain designs, particularly those intended to move water from around building foundations, utilize plastic drainage pipe to move the water to the designated area. Older buildings may have the same system using clay pipes; however, clay pipes degrade with age, causing the French drain to fail. The pipe is usually wrapped with filter cloth, which prevents the pipe inlets from being clogged with silt. The pipe is then covered with crushed rock, which is covered with a layer of sand. Soil and landscaping may then cover the trench to hide it from view.

Interior versus Exterior Foundation Drains

• French drains are often used to manage water around building foundations. When buildings are being constructed, French drains are commonly placed around the exterior of the foundation to remove water from the area. Standing water around the foundation can cause structural damage, and French drains are an important tool to maintain structural integrity. In existing buildings, when exterior systems fail, interior French drain systems may be installed. These systems are placed around the perimeter of the foundation on the inside of the building.