How to Build an Underground Drain System to Protect Your Foundation

underground drain system
  • 4-8 hours
  • Intermediate
  • 50-500
What You'll Need
Landscape cloth

A good underground drain keeps your foundation secure by channeling water away from the foundation area where it can cause thousands of dollars worth of damage and requires a great deal of labor to repair. Also known as a French drain, underground drains involve piping. The work involved in installing them is offset by the amount it can save you on home repair bills.

Where to Place It

Your underground drain should begin near the foundation so that it can remove water from that area. You need a slope of 1-foot for every 100 feet in length. The slope should end away from the house. Start by putting a stake at the starting point and then another at the finishing point. Tie a piece of twine to both ends to show you where to dig.


You don’t need to use a wide pipe for the underground drain. two inches will be more than adequate. Begin to dig the trench following the line of the twine. It should be six inches wide, and the depth should be about four times the diameter of the pipe.


Before you lay the pipe in the trench, you need to set the slope. To do so, take two longer stakes that are both the same length. Hammer one in the trench where it begins so that the top of the stake is level with the ground. Do the same at the other end. Now measure the length of each stake.

You need to adjust the depth of the trench according to the slope you need. Measure the distance of the trench. From that, you’ll be able to calculate the depth at the end of the trench. Do the necessary digging and measure again. Continue until you have the correct slope. It is vital to making the underground drain conduct water away from the foundation of the house.


Don’t lay the pipe directly into the trench. It needs to sit on a bed of gravel. Lay coarse gravel to a depth of two inches along the length of the trench. It shouldn’t be packed down; it should just sit loosely on the earth.

After that, put the pipe in the drain. The slots in the underground pipe should face downward. Cover the pipe with landscape cloth before putting a layer of gravel (about one inch) on top of it.

Top that with about the same thickness of sand. Doing so will help water drain into the trench where it can be carried away from the foundation of the house. To finish the trench, use the soil you have dug out, patting it flat. Instead of a line across the lawn, plant grass seed to fill the bare area.