How to Install a French Drain System

A French drain system diverts water below the surface to dry out wet areas in the yard.

A French drain system is a way to control water flow on a property. The system is comprised of a trench filled with a liner, gravel and a corrugated pipe. The trench slopes down and away from the area being drained so the water can discharge freely out the end of the pipe. A properly installed French drain will divert water without problems for many years. Do not install a French drain so it discharges into the yard of a neighbor or close to a building.

Things You'll Need

• Shovel
• Garden rake
• Stakes
• String
• Line level
• Tape measure
• Tamper
• Landscaping fabric
• Gravel
• 4- to 6-inch perforated pipe

Instructions

1. Dig a 2-foot wide trench that is 2 feet deeper than the frost line. Place the excavated sod and soil on one side of the trench.

2. Place stakes at 4-foot intervals in the trench. Use a hammer to insert the stakes so they do not shift.

3. Tie a string to the stake at the beginning of the trench. Wrap the string around each consecutive stake. Use a line level to ensure that the string is level between each stake. After leveling the string, push the string down ½ inch on the stake to create a slope of 1 inch for each 8 feet of trench. This is the minimum slope required for adequate drainage. If it is possible to increase the slope, increase the slope consistently through the trench. Tie the string securely to the last stake in the trench.

4. Refine the slope of the trench by creating a consistent grade throughout the length of the trench. Starting from the beginning of the trench, use a tape measure to measure the distance from the string to the bottom of the trench. Add or remove soil to maintain this space along the entire length of the trench.

5. Use a hand tamper to compact the soil at the base of the trench. Use a tape measure to double check the grade and add or remove soil to follow the grade. Remove the string and stakes.

6. Line the trench with landscaping fabric.

7. Fill the trench with 2 inches of gravel.

8. Place perforated pipe in the trench with the holes on the gravel bed. Connect as many sections as needed to line the entire trench.

9. Fill the trench about 4 inches from ground level with gravel.

10. Cover the gravel with landscaping fabric.

11. Replace with as much soil and sod to level the area with the surrounding ground level. Water the area to nourish the sod so the area will quickly blend with the surrounding landscape.

Tips & Warnings

• Monitor the French drain for possible bush or tree roots that may penetrate the perforated pipe and cause blockages. Use a spade shovel to cut roots on each side of the trench as needed. Simply press the blade all the way into the soil on each side of the trench annually to cut any possible roots.

• Wear eye protection when tamping the soil and stone to protect your eyes from flying debris.

References

• Ask the Builder: A Simple Trench Drain
• French drain line drainage advice and tips