How long does it take to install a french drain?

A 50-foot residential french drain takes one full weekend for two people with hand tools — roughly 12–16 person-hours. A rental mini-excavator cuts that to a single day. Foundation drains at 36–48 inches of depth run two to three days with machines and a spotter.

Do I need a permit to install a french drain?

Most yard drains do not require a permit, but outlets that discharge onto a neighbor's property, into a storm drain, or near a septic field usually do. Foundation drains that tie into a sump or interior drainage system typically need a plumbing permit. Call your local building department before digging.

What is the biggest mistake when installing a french drain?

Skipping the filter fabric, or using the wrong kind. Soil migrates into the rock voids within a few years and clogs the pipe perforations, and a drain without fabric usually fails in 5–10 years. Use non-woven geotextile (4–8 oz/yd²) with a 6-inch overlap at the top seam.

When should I hire a contractor instead of DIY?

Hire a contractor when the trench runs deeper than 4 feet, crosses buried utilities, passes under a driveway or patio, or requires a sump pump or dry well outlet. Foundation drains on a finished basement also usually warrant a pro — the cost of fixing a bad install after backfill is far higher than the install itself.

How to Install a French Drain — Step-by-Step Guide

A seven-step install guide covering planning, excavation, slope, pipe, rock, fabric, and outlet — for yard and foundation drains.

A french drain is one of the few drainage fixes a reasonably handy homeowner can do in a weekend. The work is physical but not complicated: dig a sloped trench, line it with filter fabric, lay perforated pipe on a bed of washed rock, surround it with more rock, wrap the fabric closed, and backfill. Get the slope and the fabric right and the drain will outlast most of the yard. Use the French Drain Calculator first to size your rock, pipe, and fabric, then work through the steps below.

Tools & Materials

Tools: round-point shovel, mattock or pickaxe, 4-foot level, hand tamper or plate compactor, utility knife, wheelbarrow, string line and stakes. A rental mini-excavator turns a weekend job into an afternoon for trenches over 40 feet or deeper than 3 feet.

Materials (size with the calculators below):

Washed #57 drainage rock — size with the French Drain Calculator or Drainage Rock Calculator
4-inch corrugated perforated pipe (6-inch for runs over 150 ft or heavy roof runoff)
Non-woven filter fabric (4–8 oz/yd² geotextile) — not woven landscape fabric
Pipe couplings and an outlet fitting (daylight, pop-up emitter, or dry well)
Topsoil or decorative gravel for the top 2–4 inches — size gravel with the Gravel Calculator

Step 1: Plan the Route and Outlet

Walk the problem area after a heavy rain. The trench should intercept water upslope of the wet zone and carry it to the lowest point you can reach. Outlets come in three flavors: daylight (trench exits on a downhill slope), pop-up emitter (spring-loaded cap in a lower lawn area), and dry well (buried perforated barrel or gravel pit where daylight is not possible).

Call 811 before you dig.Utility locates are free and take 2–3 business days. Mark your trench with spray paint and plan a minimum 1% grade — 1 inch of fall per 10 feet of run — from the upstream end to the outlet. Less slope and water sits in the pipe; a lot more is fine but wastes depth.

Step 2: Excavate the Trench

Depth:18–24 inches for yard drainage; 36–48 inches for foundation drains (always below the footing). Width:12 inches for a 4-inch pipe, 14–16 inches for a 6-inch pipe. The width leaves roughly 4 inches of rock on each side of the pipe, which is what the hydraulic math wants.

Pile spoils on a tarp along one side of the trench. On yard jobs the topsoil layer usually goes back in as the final cap; subsoil is typically hauled off or spread elsewhere since the trench is now filled with rock, not dirt. A mattock speeds up clay and root-bound sections; a plate compactor rented with the excavator is worth it on longer runs for the base prep in Step 3.

Step 3: Prep the Base to Slope

Tamp the trench bottom to firm up loose excavation. Pull a string line between two stakes from the high end to the outlet and check that every point along the bottom drops consistently — a 4-foot level laid on a straight board works for shorter runs. Correct any flat or reverse-pitched sections now. After the rock goes in, fixing slope means pulling it all back out.

Step 4: Lay Filter Fabric and Starter Rock

Roll non-woven filter fabric into the trench so that the fabric covers the bottom and both walls with enough left over to overlap across the top by at least 6 inches. Staple or pin the edges to the trench lip to keep dirt out while you work. Shovel in a 2-inch starter layer of washed #57 stone on top of the fabric and rake it smooth, maintaining the slope you set in Step 3.

Step 5: Place the Perforated Pipe

Set the perforated pipe on the starter rock with perforations facing down. This is counterintuitive — it looks backwards — but it is correct: water fills the rock envelope from the sides, and perforations-down means the pipe starts carrying water the moment it reaches the pipe bottom rather than only after it rises to the top half. Connect sections with couplings, tape joints if the manufacturer specifies, and recheck slope with a level on the pipe itself.

Step 6: Build the Rock Envelope

Backfill washed drainage rock around and over the pipe, stopping 2–4 inches below finished grade so the cap has room. Keep the rock clean — no soil mixed in, no fines, no crushed concrete. Work in 6-inch lifts and avoid dropping rock directly on the pipe from height. The goal is a uniform envelope of free-draining aggregate that lets water reach the pipe from every direction.

Step 7: Close the Fabric and Backfill

Fold the filter fabric over the top of the rock with at least a 6-inch overlap along the seam. Trim excess with a utility knife. Cap with 2–4 inches of topsoil for yards (so grass can grow) or decorative gravel for driveway edges and planting beds. Walk out to the outlet and confirm it is clear and draining — run a hose for a few minutes upstream to watch water come through.

Common Mistakes

Skipping filter fabric, or using woven landscape fabric. Soil migrates into the rock voids and clogs the perforations within 5–10 years. Non-woven geotextile is cheap insurance against the one failure mode that kills french drains.
Wrong rock. Pea gravel packs too tight and passes through pipe perforations; crushed concrete almost always carries fines that wash into the pipe. Pay the small premium for washed #57 or #67 stone.
Flat or reverse slope. Without a consistent 1% downhill grade, water sits in the pipe and the drain becomes a very expensive hole full of rock.
Perforations up. Looks right, drains wrong. Perforations face down.
Skipping the compacted base. Loose soil settles unevenly and creates low spots in the pipe that trap water and silt.
No outlet cleanout. A short stub of solid (non-perforated) pipe with a screened cap at the downstream end lets you flush the system with a hose every few years. Leave it off and you have no way to maintain the drain.

Cost: DIY vs. Contractor

DIY materialsfor a 50-foot residential french drain run roughly $300–500: rock $150–200 delivered, perforated pipe $60–100, non-woven fabric $40–80, plus fittings and an outlet. Add $150–250 for an afternoon’s mini-excavator rental if you do not want to hand-dig.

Contractor-installedfrench drains run $25–50 per linear foot on straightforward yard jobs — $1,250–2,500 for the same 50-foot run. Foundation drains, driveway crossings, sump-pump outlets, and dry wells push the number higher. Hire a pro when the trench runs deeper than 4 feet, crosses utilities you cannot safely work around, or when the drain serves a finished basement. The cost of fixing a bad install after the trench is backfilled and the slab is repoured is far higher than the install itself.

Related Calculators

French Drain Calculator— Size rock, pipe, and fabric for this install
Drainage Rock Calculator— Estimate rock for footing drains, dry wells, and under-slab drainage
Gravel Calculator— Estimate gravel for sub-bases, driveway caps, and surface layers

Written by Daniel McCarney — AceCalc