A French drain—sometimes called a perimeter drain, a rock drain, a weeping tile, an agricultural drain or a curtain drain—is an effective rainwater or water runoff management system for a home, business or commercial property. French drains protect the home or property by absorbing and redirecting excess water away from (or out of) the building and into appropriate channels such as city sewer mains or storm systems. French drains actually absorb excess water from the ground into their drains at one location and redirect it elsewhere. French drains can be installed inside of a home (such as in the basement floor), around the side of a home or building or behind an outdoor retaining wall. French drains are useful behind exterior retaining walls to prevent water from pooling and damaging a wall’s structural integrity over time.
Depending on the grade a house is sitting on, French drains are often installed between a hill and the house, says Chris Levins of CLC Contractors in Morrisville, Pennsylvania. French drains prevent water runoff from the hill from putting excess water strain on the house. French drains are not a method of waterproofing, Levins says. They are a method of water detouring—taking water from one location and putting it elsewhere via the drain.
Because installing a French drain often involves excavation, construction and plumbing, it’s typically handled by a general contractor. Several factors affect the overall cost of having a French drain installed in a house or on a property.
Cost per linear foot
Contractors often charge by the linear foot for French drain installation. The price per linear foot includes labor, materials and all other installation costs. Pricing can vary from region to region based on a variety of factors, such as the labor rates in an area and the accessibility of the job site. If workers have to hand dig the trenches, the job will take longer and the cost per linear foot will be higher than if they can drive a mini-excavator right to the site for the trench-digging process. Soil content also affects cost per linear foot, says Levins at CLC Contractors. Shale or hard-to-dig conditions increase work time and overall project costs. Here are some examples of cost per linear foot for French drain installation from CLC Contractors:
Base rate for outdoor French drain installation: $25 per linear foot
Soil content and accessibility could increase that base cost.
For example, 200 linear feet of French drain installed @ $25 per linear foot behind an exterior retaining wall using a mini-excavator: $5,000
The job took two full days and three workers.
- This property was absorbing all the runoff water from the uphill property. The new drains will discharge the uphill neighbor’s runoff into the storm system.
Basement French drain installation: ~ $45 per square foot
- Basement work is a lot more labor intensive, so costs more per square foot.
The French drains that CLC Contractors installs are a multilayer filtration system buried approximately 24 inches in the ground. CLC Contractors can excavate a trench (or trenches) in any location to absorb and redirect water. Generally, the drains are installed in a line below and directly horizontal to the water source (such as a hill). French drains can also run along a house or other site for protection from water. As water comes downhill, it will gather in the parallel-laying French drain, run through the French drain and then discharge out both sides of the drain—neatly avoiding the house or building.
When the crews at CLC Contractors dig a trench for a French drain, inside they lay a tubular drainage system wrapped in a geotextile fabric, which is water-permeable. Inside the geotextile fabric are clean stones for water to travel through, as well as a perforated pipe at the bottom, which absorbs any water coming through the multilayer filtration system. The drains are then covered back up so they are not visible above ground.
Installing French drains in a basement requires cutting into the concrete to lay the drains next to (not above) the footing of the foundation, says Levins of CLC Contractors. Contractors cut the perimeter, butt the French drains in against the foundation wall and run them to end in the home’s sump pump. The sump pump then does its job of getting the excess water out. French drains work well in basements prone to flooding as well as those with a porous foundation. Levins of CLC Contractors says that a French drain doesn’t water from a basement, but allows the homeowner to control it.
Let the contractors know about the physical accessibility of the project location. For example, can they drive their equipment right to the location? Or will they need to carry items in by hand? Hard-to-reach sites often cost more than easily accessible job sites.