How to Install a French Drain

A French drain redirects water away from your foundation by creating a gravel-filled trench with a perforated pipe that carries water to a safe drainage area.

1. Map Water Flow First. Walk your property during heavy rain to identify where water pools and flows naturally. Mark the starting point where water accumulates and trace the best path to a safe discharge area like a storm drain, dry well, or slope away from all structures. Check local codes for discharge requirements and call 811 to mark underground utilities before digging.
2. Get the Slope Right. Measure the total length of your planned drain route. You'll need a minimum slope of 1 inch per 8 feet of length for proper water flow. Calculate the depth at each end - if your drain starts 2 feet deep, a 40-foot run needs to end at least 5 inches deeper. Order 4-inch perforated drain pipe, landscape fabric, and gravel - about 1.5 tons of gravel per 100 feet of drain.
3. Break Ground with Purpose. Dig a trench 6 inches wide and 8-24 inches deep, depending on your drainage needs. Keep the bottom of the trench smooth and maintain your calculated slope using a string line and level. Pile excavated soil on a tarp to make backfilling easier. The trench should be about 3 inches wider than your pipe on each side.
4. Layer Protection and Gravel. Line the entire trench with landscape fabric, leaving enough excess to wrap over the top later. This prevents soil from clogging your drain while allowing water to pass through. Add 2-3 inches of clean gravel to the bottom and level it, maintaining your slope. Use pea gravel or 3/4-inch crushed stone.
5. Position Pipe Holes Down. Lay the perforated pipe in the trench with holes facing down. This seems backwards, but water enters from below and sides more than from above. Connect pipe sections with couplers and ensure the pipe maintains the proper slope. The pipe should sit firmly on the gravel base without rocking or shifting.
6. Wrap It Like a Burrito. Cover the pipe with more gravel until you have 2-3 inches above the pipe. The gravel layer should be at least 6 inches total thickness. Fold the landscape fabric over the top of the gravel, overlapping the edges by several inches. This creates a burrito-like wrap that keeps soil out while letting water in.
7. Finish and Mark Location. Fill the remaining trench with excavated soil, tamping gently every 6 inches to prevent settling. Leave the final surface slightly crowned to account for future settling. Restore grass, mulch, or other surface materials. Mark the drain location for future reference and maintenance.