French drain cost calculator

A French drain is a trench lined with fabric, filled with gravel around a perforated pipe, that collects groundwater and carries it somewhere it can drain away. It is priced by the linear foot, and the depth and location set the rate. We combined five cost guides. Where three or more give a range, the low is the middle of their lows, the high the middle of their highs, and the typical the middle of their midpoints.

The 100 ft column is the drain alone. HomeAdvisor's overall average is about $45 a foot, with most projects between $500 and $18,000 and an average of $9,250, a figure pulled up by basement systems. Fixr's typical basement job is about $5,000 for 100 ft.

Materials are cheap. LawnStarter and Bob Vila put perforated pipe at $0.50 to $3 a foot, and LawnStarter puts pea gravel at $25 to $53 a ton. The rest is digging, hauling soil and gravel, and putting the yard back.

By length, the guides' whole-job ranges look like this:

Fixr's narrower figures for 100 ft, $3,500 to $4,000 outside and $5,000 to $6,000 inside, sit near the middle of those ranges. The width of the ranges is mostly depth: a shallow trench a mini excavator can cut in a morning, against a deep one along a foundation that takes days.

• Shallow exterior drain. A trench 1 to 2 ft deep across a soggy part of the yard or along the house, carrying surface and shallow groundwater to a lower spot, the street or a dry well. The most common kind.
• Curtain drain. A shallow drain placed uphill of the area you want to keep dry, catching water before it gets there. HomeAdvisor puts it at $10 to $25 a foot, the cheapest of the types.
• Footing drain. A deep drain dug down to the bottom of the foundation, around the outside of the house, to relieve water pressure on basement walls. It means excavating along the foundation, often with a machine, so it costs much more. Best done when a house is built or when the foundation is being waterproofed from outside.
• Interior drain. Cut into the basement floor along the walls, it catches water coming through the walls or up from below and sends it to a sump pump. Fixr notes interior drains need a sump pump to work, so the calculator always includes one.

Bob Vila also lists rates by location: $20 to $30 a foot in the yard, $25 to $40 around a patio, $25 to $50 along a retaining wall, $25 to $35 in a crawl space, $50 to $80 around the house and $60 to $70 in a basement.

A drain needs somewhere to send the water. If the yard slopes to the street or a ditch, the pipe can daylight there. If it does not, the options are a dry well, a gravel pit or buried tank that lets water soak in slowly, or a sump pump that lifts it out. Bob Vila puts gravel or plastic dry wells at $50 to $700 and concrete ones up to $3,000.

Soil matters too. HomeAdvisor notes rocky or clay-heavy soil takes longer to dig, and the crew's hourly rate does not change when the shovel stops moving.

A backyard stays soggy for days after every storm and water pools against the back of the house. The fix is a 100 ft shallow French drain along the back of the yard, running downhill to the side of the lot.

• Drain. 100 ft × $10 / $30 / $50 = $1,000 / $3,000 / $5,000.
• Lawn repair. $100 / $150 / $200.
• Permit. $50 / $125 / $200.
• Total. $1,150 to $5,400, with $3,275 typical at the US average.

LawnStarter's 100 ft exterior range, $1,000 to $6,500, and Lawn Love's, $1,000 to $7,500, bracket it. Had the yard no downhill outlet, a dry well would add about $1,638 typical. Had the water been coming into the basement instead, a 100 ft interior drain with its sump pump would run about $4,625 to $12,000, $8,325 typical, before the permit, because the floor has to be cut, dug out and patched with new concrete. Enter a ZIP in the calculator to scale the labor share to your state's wages.

A shallow yard drain is one of the more doable drainage jobs for a fit homeowner. Lawn Love works out a 25 ft DIY drain at about $528 in materials, or $21.12 a foot, and points out that this can come close to a pro's price on short runs once you count your time. LawnStarter puts a trencher rental at about $85 a day.

• Slope. The trench needs a steady fall toward the outlet. Fixr gives the ideal as 1 in for every 8 ft of run, and never less than 1%. Check it with a string line or a level, because a drain with no slope just holds water.
• Fabric first. Line the trench with landscape fabric before the gravel, and wrap it over the top, so soil does not clog the stone.
• Pipe. Use perforated pipe, ideally with a fabric sock in fine soil, which Bob Vila notes helps keep silt out. The pipe runs on a bed of gravel and is covered with more.
• Clean outlet. Finish at a pop-up emitter, a dry well or open ground lower than the trench, never against your own foundation or onto a neighbor's lot.

• Standing water in the same part of the yard for a day or more after rain.
• A wet or damp basement, or water at the joint where the floor meets the wall.
• Soil washing away along the house or down a slope.
• Water running toward the house from a neighbor's higher yard.
• Mold or a musty smell in a crawl space.

Lawn Love notes a curtain drain is only 9 to 12 inches deep and suits sloped yards where water runs down toward the house. HomeAdvisor describes exterior perimeter drains as about 2 ft deep next to the foundation, sloping away from the house. Neither needs the heavy digging of a true footing drain, which is why they cost so much less. If the problem is water in the basement during long wet spells, rather than a soggy lawn, the deeper fix is usually the one that works.

Before you dig, check the easy fixes. Clogged gutters and downspouts that dump next to the house cause much of the water people blame on groundwater. Extend the downspouts and make sure the soil slopes away from the house. If that does not fix it after a season of rain, a French drain is usually the next step. For water already in a basement, see our basement waterproofing cost calculator, and for cracks and settling, the foundation repair cost calculator.

• Price per foot by depth. Shallow, curtain, footing and interior are different jobs. Quote the depth on the estimate.
• Price the outlet. Daylighting, a pop-up emitter, a dry well or a sump each go on their own line.
• Price access and restoration. Fences, patios, mature plantings and sod replacement all add time.
• Call 811 and note it on the job, and get the permit where it is needed.
• Mind the margin. Our profit margin calculator shows the price that keeps it.

The "Save as an estimate" button above turns the result into lines. Send it from Koira and the customer can sign and pay a deposit on their phone.