How to Build a French Rock Drain


If you have leaky walls or a damp basement in your house, a French drain may be just what you need. Also known as a trench drain, the French drain is a simple system to channel water away from your house, preventing it from leaking through the foundation. When it rains, water trickles through a layer of gravel into an underground drainage pipe, which then flows downhill, draining out at a lower point on your property.

Things You'll Need

  • Shovel
  • Tamping tool
  • Gravel
  • Pipe
  • Sod
  • Contact the utility companies and have them mark out all utility lines on your property.

  • Plan the route of your French drain. The French drain should surround three or four sides of your house at about four to six feet from the foundation. It should then flow downhill and emerge at a low spot in your property where the water won't do any damage. Mark out the path of the drain with rope, stakes or some other marking.

  • Dig a trench half a foot wide and between 10 inches and two feet deep. The trench around your house should slope down slightly so that the low point is where it connects to the downhill spout. The downhill spout should slope down at a continuous rate, ideally lowering six inches every 50 feet or more. At the bottom, the pipe should emerge from the drain. If you need to, remove dirt from your property around the bottom end of the pipe so that it clears the ground. This will allow the water to flow out of the pipe more freely after it drains down, making it operate much more efficiently.

  • Use a tamping tool such as a 4-by-4 to compact and even out the soil at the bottom of the trench. Place one to two inches of washed, round gravel at the bottom of the trench.

  • Install a four-inch perforated plastic drainage pipe at the bottom of the trench with the holes facing down. Connect the pipe so that it forms an unbroken channel from the top of the drain to the bottom, where is should stick out of the ground

  • Fill in the trench with washed gravel all the way to the surface. Alternately, leave one to two inches at the very top and install a thin strip of sod on top of the gravel.

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