French Drain Installation Cost: What Changes a Bid
A french drain installation cost is built from six things: how many linear feet of trench, how deep that trench has to go, whether the drain runs outside in the yard or inside along a basement footing, what the trench has to cross to get there, where the water is allowed to go at the far end, and how much surface has to be put back afterward. Depth and discharge are the two that move the number most, and they are also the two that homeowners never ask about.
Length is the number everyone fixates on, and it matters least per foot. A 40 foot shallow curtain drain across a lawn and a 40 foot interior drain tile system under a basement slab share a name and nothing else.
Updated September 2026
A note on numbers. No dollar figures on this page. Excavation, stone, pipe, disposal and restoration pricing swing hard by region, by soil and by season, and a printed range would be wrong for most readers and out of date for the rest. What follows is the specification, the math you can run yourself, the line items that belong on a written bid, and the questions that keep three quotes honestly comparable.
Stone is the single biggest material on the ticket, and you can price it yourself. Take your trench length, width and depth and get the volume and tonnage from our free Gravel Calculator. Walking into a bid conversation knowing the job needs about six tons of washed stone rather than two changes the whole tone of the meeting.
The four things people call a french drain
Get the type right first, because bids for different types are not comparable at all.
| Type | Where it sits | Typical depth | What it solves |
|---|---|---|---|
| Surface or yard drain | Shallow trench in the lawn, often with grates | 12 to 24 inches | Standing water, soggy low spots, roof runoff |
| Curtain drain | Uphill of a structure, cutting off flow | 18 to 36 inches | Water sheeting toward the house from a slope |
| Exterior footing drain | Against the foundation, at footing level | Often 6 to 8 feet | Hydrostatic pressure on the foundation wall |
| Interior drain tile | Inside the footing, under the basement slab | Slab plus footing depth | Water already entering the basement |
An exterior footing drain means excavating the full depth of the foundation, which usually means moving the deck, the AC condenser, the shrubs and sometimes the driveway. Interior drain tile means saw cutting and removing a perimeter strip of the basement floor and hauling the concrete out through the house. Neither is a weekend project, and the difference between them is enormous in both scope and disruption. Our basement waterproofing cost breakdown compares the two systems in more depth.
What drives a french drain installation cost
Read a bid in this order.
1. Depth. A 24 inch trench can often be dug with a small machine or a trencher in a single pass. A 7 foot excavation against a foundation needs a real excavator, sloped or shored walls for safety, somewhere to stack a lot of spoil, and care not to undermine the footing. Depth changes both the machine and the risk.
2. Interior or exterior. Interior work adds concrete saw cutting, jackhammering, hauling broken slab out through a finished house, dust containment, and a new concrete pour at the end. Exterior work adds landscaping, hardscape and access problems.
3. Discharge point. This is the hidden fork. If the ground falls away and the drain can daylight to open air, gravity does the work and the job ends at the trench. If there is no fall, the system needs a basin, a pump, a check valve, a buried discharge line, and a dedicated electrical circuit. That is a completely different scope. Some jurisdictions also prohibit discharging to the street or a neighbor's property, and connecting a foundation drain to the sanitary sewer is illegal in most places.
4. What the trench crosses. Lawn is easy. Then plantings, then a paver patio, then a concrete walk, then a driveway, then a utility corridor. Every crossing adds saw cutting, hand digging and restoration.
5. Stone and pipe volume. Washed angular stone is heavy, and every ton has to be moved from the truck to the trench, sometimes by wheelbarrow if the machine cannot reach.
6. Spoil disposal. Ten cubic yards of clay has to go somewhere. On site spreading is cheap. Hauling off is not.
7. Restoration. Sod, seed, mulch beds, concrete, pavers, interior slab patch and floor finish. Ask exactly what is included.
The anatomy of a drain that actually works
A quote should describe all of this. If it does not, the bidder either assumes you do not care or is planning to skip something.
- Trench width of roughly 10 to 18 inches for a residential drain, wide enough to place stone around the pipe on all sides.
- Filter fabric lining the trench, wrapped up the sides and lapped over the top of the stone. This is the part that keeps silt out and keeps the drain working in year ten. Non woven geotextile is the usual choice.
- Perforated pipe, commonly 4 inch. Rigid slotted PVC or SDR-35 cleans out better and holds grade better than corrugated flex pipe. Corrugated is cheaper and faster and is fine in easy applications.
- Washed angular stone, typically a #57 or #67 crushed stone around 3/4 inch. Rounded pea gravel packs tighter and drains worse. Unwashed stone brings its own silt to the party.
- A minimum slope of 1 percent, which is 1/8 inch of fall per foot of run. Less than that and solids settle in the pipe.
- Stone cover over the pipe, generally at least 6 inches before the fabric closes over the top.
- Cleanouts at the ends and at any change of direction, so the line can be jetted later.
- A defined outlet, either a daylight discharge with a rodent grate or a basin with a pump.
The debate about which way the pipe holes face is settled by physics: holes down. Water enters the pipe at the bottom, and the drain starts working before the trench fills. Some installers still lay them up out of habit.
Worked example: stone and slope for a 60 foot drain
Say you need 60 feet of curtain drain along the uphill side of the house, 12 inches wide, starting 24 inches deep and daylighting at the low corner.
- Trench volume: 60 ft x 1 ft wide x 2 ft deep = 120 cubic feet.
- Subtract the pipe: a 4 inch pipe has an outside diameter near 4.5 inches, so its cross section is about 0.11 sq ft. Across 60 ft that is roughly 7 cubic feet.
- Stone volume: 120 minus 7 = 113 cubic feet, which is 113 / 27 = about 4.2 cubic yards.
- Tonnage: washed 3/4 inch stone runs near 1.4 tons per cubic yard, so 4.2 x 1.4 = about 5.9 tons. Order 6 tons and expect to be short if you spread any of it as a driveway repair while the truck is there.
- Slope: at 1 percent, 60 feet needs 60 x 0.01 = 0.6 ft of fall, which is about 7.2 inches. So the trench bottom starts at 24 inches and finishes near 31 inches at the outlet.
- Backfill on top: if you want 4 inches of topsoil and sod over the fabric, that comes out of the 24 inches, so the stone bed is really about 20 inches deep at the shallow end.
That last item is the one people miss. A drain built to daylight has to keep falling the entire way, so the deep end of a long run gets deep fast. On a 100 foot run at 1 percent you have gained a full foot of depth by the outlet, and that is often what pushes a simple job into machine work.
The line items that belong on a written bid
| Line item | What the bid should specify |
|---|---|
| System type | Yard drain, curtain drain, exterior footing drain, or interior drain tile |
| Length | Linear feet, and where the run starts and ends |
| Trench | Width and depth at both ends, and the slope percentage |
| Fabric | Non woven geotextile, and that it wraps the stone completely |
| Pipe | Diameter, rigid slotted or corrugated, and perforation orientation |
| Stone | Type and size, washed, and the tonnage or yardage |
| Cleanouts | How many and where |
| Discharge | Daylight outlet with a grate, or basin, pump, check valve, discharge line and freeze protection |
| Electrical | Whether a dedicated circuit and outlet for the pump are included, or excluded |
| Spoil | Spread on site or hauled away |
| Utility locate | That 811 was called before digging, with the ticket number |
| Restoration | Sod or seed, mulch, concrete thickness and finish, paver reset, interior slab patch |
| Permits | Whether one is required and who pulls it |
| Warranty | Workmanship term, and whether it promises a dry basement or only the installation |
That last row deserves attention. A workmanship warranty on the installation and a performance warranty that the basement stays dry are different promises. Ask which one you are buying, and read what voids it.
Interior versus exterior, decided honestly
| Factor | Interior drain tile | Exterior footing drain |
|---|---|---|
| Disruption | Inside the house, dust, noise, a week of mess | Outside, but landscaping and hardscape suffer |
| Excavation | Saw cut and remove a perimeter strip of slab | Full foundation depth excavation |
| Waterproofing benefit | Manages water after it reaches the footing | Keeps water off the wall in the first place |
| Wall treatment | Often paired with a dimple board on the inside face | Allows exterior membrane and drainage board |
| Weather | Can be done in winter | Weather dependent |
| Access | Needs interior clearance along the walls | Needs machine access around the house |
| Typical use | Retrofit on an existing finished or partly finished basement | New construction, or a full exterior restoration |
Contractors tend to sell whichever one they do. That is not dishonest, it is specialization, but it means you should get at least one bid from each camp so you hear both arguments. If the water is already coming through a specific crack rather than across the whole floor, read our basement leak repair guide before committing to a whole perimeter system, because a single injected crack is a much smaller job.
What changes the number after work starts
- Rock or ledge. Hitting shale, cobbles or hardpan two feet down turns a trencher job into a hammer job.
- A high water table. A trench that fills as fast as you dig needs a pump running the whole time and unstable walls need shoring.
- Buried utilities. Public lines get marked by 811. Private ones do not: irrigation, invisible fence, gas to a fire pit, landscape lighting, a well line, or an old water service. If the crew finds one, everything stops. Our guide to water line repair covers what happens when a buried water service is nicked.
- No gravity outlet after all. Sometimes the survey looks fine and the actual grade does not cooperate. That adds a basin, a pump and a circuit.
- Existing crushed drain tile. Old clay tile or a collapsed corrugated line found in the trench usually gets replaced rather than tied into.
- Slab thickness. Interior work priced on a 4 inch slab meets a 6 inch slab with wire mesh and takes far longer to cut and break out.
- Footing depth surprises. A stepped footing, a bump out or an old addition on a different footing changes the trench profile.
- Tree roots. Cutting structural roots is slow and risks the tree, and homeowners often change the route once they hear that.
- Discharge restrictions. A city rule against discharging to the street or the storm sewer can force a dry well or a long buried run to a legal outlet.
- Radon. Opening a slab is a good moment to add a sub slab depressurization stub, and it is much cheaper now than later.
Ask every bidder to price the pump scenario as a named alternate, even if they expect a gravity outlet. Then a mid job discovery is a line you already agreed to rather than a negotiation in your driveway.
How to compare bids apples to apples
- Match the system type. An interior bid and an exterior bid are not two prices for the same thing.
- Match the length and the depth. Ask each bidder for the trench depth at both ends and the slope they plan.
- Match the stone. Washed #57 and a screening or bank run gravel are very different materials, and one of them fails in five years.
- Match the pipe. Rigid slotted with cleanouts against corrugated flex with none.
- Force the discharge line into the open. Gravity or pump. If pump, is the electrical included or excluded?
- Force restoration into the open. Sod, seed or bare dirt. Concrete replaced or not.
- Read the warranty terms side by side, and ask what voids each one. Gutters that dump at the foundation void more warranties than anything else.
The bid comparison discipline in our how to get contractor bids walkthrough applies directly. So does the advice in contractor red flags, because basement water is a fear driven purchase and the sales pressure around it is real.
Do the cheap fixes first
A surprising share of wet basements are gutter and grading problems wearing a drainage costume. Before you buy a perimeter system, spend a weekend on this.
- Clean and extend the gutters. A single downspout dumping at the foundation can deliver hundreds of gallons in one storm. Our gutter cleaning guide covers the routine, and extensions should carry water at least 6 feet from the wall, further on clay.
- Fix the grade. You want roughly 6 inches of fall in the first 10 feet away from the foundation. Settled backfill against a house sends every roof gallon straight down the wall.
- Check the window wells. A well with no drain and no cover is a bucket sitting against your basement.
- Test the sump pump you already have. Half the "the system failed" calls are a stuck float or a dead check valve. Walk through our sump pump test before assuming the drain is the problem.
- Chase the smell, not just the water. A basement that smells damp without visible water is often a humidity and vapor problem, which is a different fix. Our guide to musty basement smell sorts those out.
Doing these first is not a way to avoid the drain. It is how you find out whether you need one, and it makes any drain you do install last longer.
Frequently asked questions
How deep does a french drain need to be?
Deep enough to intercept the water you are trying to catch, and no deeper. A yard drain collecting surface water works at 12 to 24 inches. A curtain drain cutting off flow from a slope usually wants 18 to 36 inches, ideally into the first dense soil layer. A footing drain has to reach the bottom of the foundation footing, which is whatever your frost depth and construction dictate.
What slope does the pipe need?
A minimum of 1 percent, which is 1/8 inch of drop per foot. Steeper is fine and drains faster. Flatter lets sediment settle in the pipe and eventually blocks it. On long runs, remember that the slope compounds: 100 feet at 1 percent means the outlet end sits a full foot deeper than the start.
Should the holes in the pipe face up or down?
Down. Water enters through the lowest openings, so the pipe starts carrying water before the surrounding stone floods. Holes up means the trench has to fill to the top of the pipe before anything moves, which is the opposite of what you want.
Can I use pea gravel instead of crushed stone?
You can, but crushed angular stone drains better. Rounded pea gravel nests tightly and leaves less void space for water to move through. Whatever you use, it has to be washed, because unwashed stone carries its own fines that silt the fabric from the inside.
Do I need filter fabric?
Yes, in almost every soil. Fabric keeps silt out of the stone bed, and silt is what kills these systems. Line the trench, place stone and pipe, then fold the fabric over the top before backfilling. A pipe sock alone is not a substitute in fine or silty soils, because the sock clogs and the pipe is then sealed off.
How long does a french drain last?
A properly built system with washed stone, a wrapped fabric envelope, correct slope and cleanouts can run for decades. The ones that fail early almost always failed on materials or slope: unwashed stone, no fabric, a flat run, or a discharge that backs up. Cleanouts are what let you jet the line and buy another decade.
Will a drain alone keep my basement dry?
Not on its own. A drain manages the water that reaches it. Gutters, downspout extensions, grading and window well drainage all decide how much water shows up in the first place. The homes that stay dry after a system goes in are the ones where those surface issues got fixed at the same time.
