How to Install a French Drain

Intermediate · 1–2 days

A French drain is a gravel-filled trench with a perforated pipe that gives water an easy path away from where you don't want it — a soggy yard, a wet basement wall, or a low spot that never dries. The whole thing works on gravity, so the one number that matters most is slope: a consistent fall from the inlet to the outlet. Get the slope right and wrap the gravel in filter fabric, and the drain runs silently for decades. Get it flat and it becomes a buried puddle.

What you'll need

• Drainage gravel (use the calculator to size cubic yards and tons for the trench)
• Perforated drain pipe (rigid is better than corrugated for flow and cleaning)
• Non-woven filter / landscape fabric to wrap the gravel
• A shovel or trenching tool, and a wheelbarrow for spoil
• A line level, string, and a tape measure to set and check the slope
• A drain outlet (daylight, dry well, or pop-up emitter)

Steps

1. 1

   Plan the route and outlet

   Identify where water collects and where it can safely go — downhill to daylight, a dry well, or a storm drain (check local rules). Call 811 to locate utilities before digging.

2. 2

   Dig the trench to slope

   Dig the trench about 12 in wide and deep enough to carry water below the problem, maintaining at least a 1% fall (about 1 in per 8 ft) from inlet to outlet. Check the grade with a string and line level as you go.

3. 3

   Line the trench with fabric

   Lay non-woven filter fabric in the trench with plenty of overlap up the sides — you'll fold it over the top later. The fabric keeps silt out of the gravel so the drain doesn't clog.

4. 4

   Add a gravel base

   Pour a few inches of gravel along the bottom and rake it to follow the slope. This bedding cradles the pipe and keeps it draining freely.

5. 5

   Lay the perforated pipe

   Set the perforated pipe on the gravel bed with the holes facing down (so water enters from below and the pipe carries it out). Confirm it falls continuously toward the outlet.

6. 6

   Backfill with gravel

   Fill around and over the pipe with gravel, leaving a few inches below the surface. Keep the gravel clean — fines and dirt are what clog a drain over time.

7. 7

   Wrap, cap, and restore the surface

   Fold the fabric over the top of the gravel to fully wrap it, then top with a few inches of soil and sod or a decorative stone strip. Confirm the outlet daylights cleanly so water exits.

Pro tips

• Slope is everything. A continuous fall of at least 1% (1 in per 8 ft) is what makes a French drain work — a flat trench just stores water underground.
• Always wrap the gravel in non-woven filter fabric. Silt washing into bare gravel is the number-one reason French drains clog and fail.
• Point the pipe perforations down. Water rises into the pipe from the saturated soil below and the pipe carries it away — holes up lets sediment settle in.
• Use rigid perforated pipe over flimsy corrugated where you can; it flows better and can be snaked out if it ever clogs.

FAQ

Ready to estimate materials? Use the French Drain Gravel Calculator →