French Drains: When You Need Them
If you have a soggy yard or a wet basement, the solution may be an exterior or interior French drain (weeping tile), a channel that collects water and diverts it safely away.
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 perforated pipe that's used to divert underground water away from your house. The name does't come from the country. It's from Henry French, a judge and farmer in Concord, Massachusetts, who promoted the idea in an 1859 book about farm drainage. French made his drains with clay tiles, but installers today usually use 4-inch-diameter plastic pipes. If you live on a slope and have a persistently wet basement or soggy lawn, a French drain (weeping tile) could be the solution.
How a French drain works
French drains work by providing an easy channel for water to flow. Surface and subsurface water runs through the spaces between the round gravel and into the perforated pipe at the bottom of the trench. Water then travels freely through the pipe, which empties a safe distance from the house. The trench bottom should be sloped about 1 inch for every 8 feet in the direction you want water to flow. Depending on the situation, the water can be diverted to a low-lying area of the property, a drainage ditch, a dry well, or the street.
Build a French drain into a retaining wall
If you're building a retaining wall on a hillside, incorporate a French drain (weeping tile) behind the first course of stones or blocks. Otherwise water moving down the hill will build up behind the wall and undermine or even tip it. The pipe should rest on the same compacted gravel base or concrete footing that supports the wall. To protect the drain from clogging with silt, drape landscape cloth across the base or footing and up the slope before you add the pipe and drain gravel. As you near the top of the wall, fold the cloth over the top of the gravel, and top with several inches of soil.
Interior French Drain (Weeping Tile) System
Add an interior French drain (Weeping Tile) to remove water where it enters
If you can't keep water out of your basement, you can build an interior French drain (weeping tile) to intercept the water where it comes in. Crews cut a channel around the perimeter of the basement floor, chip out the concrete, and install perforated pipe all the way around. Solid pipe then carries the water to a collection tank sunk into the floor, and a sump pump sends it out to the yard or a storm drain. The channel is patched with a thin layer of concrete, except for a small gap at the edge to catch any water that dribbles down the wall.