How a french drain install actually goes
A french drain job starts with finding where the water actually comes from. A good crew watches how the yard drains, checks downspouts, and looks for the low, wet spots. That diagnosis sets the whole plan, because an exterior yard drain and an interior basement drain are very different jobs.
The core of the work is a trench cut on a steady slope so water flows by gravity. The crew lines the trench with filter fabric, sets a perforated pipe, and surrounds it with washed gravel. The fabric wraps the gravel to keep silt out, and the pipe runs downhill to a discharge point.
An exterior curtain drain daylights to a lower spot or a catch basin, then the crew backfills the trench. An interior perimeter drain runs along the footing, ties into a sump pump and basin, and ends with new concrete poured over the slab. That concrete cutting and re-pour is why interior work takes longer and costs several times more per foot.
What really moves your price
The biggest line is interior versus exterior. An exterior drain is trenched in open soil, but an interior drain means breaking out the basement slab, laying pipe, and pouring the concrete back. Cutting and restoring that slab is slow, dusty work, and it drives the per-foot rate far higher.
Length scales the whole job, since a french drain is priced per linear foot. Trench depth matters too, because a deeper trench moves more soil and may hit hard clay, rock, or utilities. A long run to a legal discharge point adds pipe, digging, and time.
Restoring the site adds real cost that is easy to miss in a quote. Trenching across a lawn, patio, driveway, or garden bed means you pay to put that surface back. The calculator above lets you test how length, depth, and interior versus exterior change the total.
Drainage done right so it lasts
A french drain lives or dies on slope. The pipe must fall steadily toward the outlet, or water sits, silt settles, and the drain clogs. A careful installer checks the pitch along the whole run, not just the ends.
Filter fabric is not optional on a drain meant to last. It wraps the gravel and pipe so fine soil cannot wash in and choke the flow. Skipping fabric saves a little now and silts the pipe shut in a few seasons.
Where the water goes is a legal question, not just a technical one. A drain cannot dump onto a neighbor, into a septic field, or back against your own foundation. The outlet should daylight to a safe low spot, tie into a sump, or reach an approved storm connection, and downspouts should stay separate from the footing drain.
How to hire and vet the contractor
Hire a contractor who does drainage and waterproofing as core work, not as a side job. Ask what they installed on similar lots and how they decided where the water starts. The person who diagnoses the water source should be the person who stands behind the fix.
Insist on an itemized quote that separates the parts of the job. Exterior trenching, gravel, pipe, and fabric should be listed apart from any concrete cutting and re-pour. A blended per-foot number hides where your money goes and makes bids impossible to compare.
Get the warranty in writing and read what it actually covers. A real wet-basement warranty promises a dry result, not just sound workmanship. Confirm it covers the exact problem you hired them to solve, and ask how long the coverage runs.
Red flags and ways to avoid overpaying
Be careful when a contractor wants to ring your entire yard or full basement perimeter. If only one area is wet, draining the whole property can double the length you pay for. Ask why each foot is needed and what problem it solves.
Watch for pressure to go interior when an exterior fix would work. Interior slab drains are the right answer for some basements, but they cost far more than trenching outside. A crew that reaches for the expensive option first, without checking outside, is a warning sign.
Reject shortcuts on the details that make a drain last. No fabric, no measured slope, and a vague per-foot bid all point to a drain that will silt up and fail. Get clear pricing, a real discharge plan, and a warranty that does not exclude the water you are trying to stop.