How to Build a French Drain
The classic residential French drain — a step-by-step from trench to daylight.
1. Excavate
Dig a trench roughly 12" wide and 12"–24" deep, sloped 1% minimum toward daylight or a collection point.
2. Wrap with fabric
Line the trench with non-woven filter fabric, leaving enough overhang on both sides to wrap over the top after the rock is placed. This is the most-skipped step and the biggest cause of failure.
3. Bed with drain rock
Add 3"–4" of 3/4" washed drain rock at the bottom to seat the pipe.
4. Place perforated pipe
Lay 4" perforated pipe with perforations facing DOWN, sloped toward daylight.
5. Cover with drain rock
Backfill with drain rock to within 4" of grade.
6. Close the fabric and cap
Fold the fabric over the top, then top with soil or sod as needed.
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