What is a French Drain?

French drains, also called weeping tiles or sub-surface drains, are a type of outdoor drainage system used to remove excess water from the soil around foundations or other areas. These drains consist of a perforated pipe installed in a trench and covered with gravel or other porous material. The perforations in the pipe allow water to enter and be carried away by the drain, while the gravel or other material helps filter out debris. French drains are often used to prevent water accumulation near building foundations, which can cause damage over time. They can also be used to prevent erosion, reduce the risk of flooding, and improve overall drainage in various settings including residential, commercial, and agricultural properties.

How is a French Drain Installed?

Installing a French drain involves the following steps:

1. Determine the location: Assess flood-prone areas in your yard to determine the best location and route for the drain. It is important to determine where the water should go and ensure that the exit or drainage end of the trench is in a suitable location. Consider the practical effects of an exposed gravel channel on traffic routes, views, or recreation areas.

2. Check the slope: A French drain must be sloped to carry water to its destination. A minimum slope of 1% (a drop of 1 foot for every 100 feet in length) is recommended. Keep in mind that steepness increases water velocity and can lead to more erosion in the discharge area. To check the natural slope, drive a stake at the beginning and end of the planned trench route, tie a mason’s line tightly to one stake, and run it over to the other stake. Attach a line level to the line, adjust it so it is level, and measure the slope at regular intervals. Adjust the depth of the trench as needed to create the desired slope.

3. Dig the trench: Begin by cutting a straight line through the sod 3 inches to one side of the line using a square garden spade. Repeat on the other side for a total trench width of 6 inches. Remove the sod and dig the trench, creating vertical sides and a smooth, sloped bottom. Measure down from the line frequently to check the slope of the trench bottom. Make the trench as deep as desired. Compact and smooth the bottom of the trench as you go.

4. Line the trench with fabric: Line the trench with landscape fabric, overlapping pieces by at least 12 inches and securing the ends with fabric staples. Fold back excess fabric to both sides of the trench and trim it to fit later.

5. Fill the trench: Fill the trench with course drainage gravel, such as crushed granite, so it is flush with the surrounding ground or sod. Rake the top of the gravel so it is smooth and even with the top of the trench. Alternatively, you can overfill the trench slightly and rake the gravel into a mound (highest in the center) so the trench is more visible. Trim excess landscape fabric along the edges of the trench using a utility knife.

How Long Does it Take to Install a French Drain?

Installing a French drain typically takes a professional team six (6) to eight (8) hours to complete from start to finish. This time may be increased if there are obstacles that need to be worked around or concrete that needs to be broken and replaced. During the process of foundation repair, earth will be removed from around the home to gain access underneath the foundation. If you have a French drain installed while having your home foundation repaired, you will save yourself both time and money.

How Much Does it Cost to Install a French Drain?

The cost of installing a French drain can vary widely due to various factors that can impact prices. Labor is typically the biggest expense for a French drain installation, and the cost may increase if your property also requires a catch basin drain or a pop-up emitter installation. Connecting your gutter system to another landscape drainage system may also increase the cost. In some cases, the cost may be higher if concrete needs to be cut or removed and machinery is required.

Factors that can impact the cost of a French drain include the presence of pool equipment, utility lines, lawn sprinkler systems, patios, driveways, trees, shrubbery, fences, and the size, length, and depth of the drain. The cost of a French drain can start at around $3500 and go up from there, and the cost may also include the cost of any necessary permits.

If you are having your foundation repaired and having a French drain installed during that time, the overall cost is significantly reduced and in some cases can be as little as an additional $1000.