The essentials in 30 seconds
A French drain is a trench lined with filter fabric, filled with gravel and fitted with a perforated pipe. It collects water from soggy ground and carries it, by gravity, to somewhere lower: a swale, a ditch, a dry well, a storm sewer or a slope where it can spill out safely. It is the right fix when water collects below the surface or in a strip of yard you cannot regrade. It is the wrong fix when the real problem is a gutter, a short downspout or soil sloping toward the house, which are cheaper to solve first. Shallow yard drains of 8 to 24 inches are a reasonable DIY job; deeper drains, or drains close to the foundation, are work for a drainage contractor.
- Call 811 a few business days before you dig; the line-marking service is free.
- The pipe needs a continuous fall to the outlet; a drain with no lower outlet is just a buried pond.
- Check your plan will not send water onto a neighbor's property; rules vary by town, county and state.
What a French drain is and how it works
Gravel lets water through far faster than soil, so a gravel-filled trench becomes the easiest path for water in the ground around it. The perforated pipe speeds it to the outlet, and the fabric keeps fine soil from washing in and clogging the gravel.
Delaware's flood adaptation program describes French drains as trenches with filter fabric, gravel and a plastic perforated pipe that route water away from a pooling area and the foundation to a natural drainage point such as a stream, swale, ditch or slope. In the UK the term is the same; a gravel pit that lets water soak away underground is called a soakaway there, and a dry well in the US.
Interior French drains
An "interior French drain" is a different job: a perforated pipe laid around the inside edge of a basement, under or at the edge of the slab, that drains to a sump pump. It deals with groundwater pushing up into a basement, and it involves breaking concrete. Delaware notes that a yard French drain may not stop seepage into a basement or crawl space, so if your problem is a wet basement, read our basement waterproofing and sump pump guides first.
French drain, swale, dry well or regrading: which one you need
Start with the cheapest fixes. Many "drainage problems" are roof water landing in the wrong place.
| What you see | Likely cause | Best first fix |
|---|---|---|
| Puddles or erosion right under a downspout | Roof water dumped next to the house | Extend the downspout at least 5 feet from the foundation onto a splash block; see gutter cleaning |
| Water pooling against the foundation all along one side | Soil sloping toward the house, or settled backfill | Regrade so the soil falls away from the wall |
| Surface water sheeting across the yard from uphill | Runoff from a slope or a neighbor's lot | A grassed swale to intercept and redirect it |
| Ground that stays soggy for days, even without sheeting water | Water trapped below the surface, often in clay | A French drain to a lower outlet |
| A low spot with nowhere lower to drain to | No outlet on the lot | A dry well or rain garden, if the soil absorbs water |
| Water coming up through the basement floor | High groundwater | Interior drainage to a sump pump |
| Option | How it works | Best for | Limits |
|---|---|---|---|
| Regrading | Reshapes the soil so water runs away from the house | Water pooling at the foundation | Needs room; landscaping and paving settle over time and need rechecking |
| Downspout extension | Moves roof water at least 5 feet from the wall | Wet spots under downspouts | Must discharge onto your own land, not across a path or a neighbor's lot |
| Swale | A shallow, grassed channel that carries surface water | Runoff crossing the yard | Needs space and a gentle, even fall |
| French drain | Buried gravel trench and pipe that collect water underground | Soggy ground; narrow side yards | Needs a lower outlet; can clog over the years |
| Dry well (soakaway) | Buried gravel pit that stores water and lets it soak in | Small volumes with no outlet available | Fails in clay or where groundwater is high |
| Rain garden | Planted hollow that holds water briefly | Downspout water and lawn runoff | Needs soil that drains within about two days |
Get the grading right first
The DOE Building America Solution Center, citing ENERGY STAR, asks for planted ground to slope away from the house at least 0.5 inch per foot for 10 feet, and the International Residential Code asks for paved surfaces within 10 feet of the foundation to fall 2 % away from it. Where there is less than 10 feet of space, the same guide suggests a swale or a drain to carry water away. The University of Nebraska–Lincoln Extension advises extending downspouts at least 5 feet from the foundation.
When a swale beats a drain
A swale is open, cheap and easy to inspect. Building America describes a good one as trapezoidal or bowl-shaped, with side slopes no steeper than 3 to 1 and a steady fall of 2 to 4 % along its length: below 2 % water pools, above 4 % it starts to erode the channel. Keep it free of leaves and sticks, which compost and fill it. Where space is tight, or water comes from below the surface, a French drain is the better choice, and the two are often combined: a swale with a drain at its base.
How to install a French drain
These steps follow the specification in DOE's Building America Solution Center for a drain that protects a house. Simple yard drains can be shallower: Delaware puts them at 8 to 24 inches deep.
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01
Find the outlet first
Decide where the water will go: a drywell, a storm sewer where your town allows it, a ditch or swale, or a lower part of your lot. The outlet must be lower than every point of the drain.
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02
Call 811 and check the rules
Request line marking, then ask your city or county about permits and stormwater rules. Many places require you to keep runoff on your own lot.
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03
Mark the route
Run a string line from the high end to the outlet and check that it falls all the way. Keep trees and shrubs away from the line, since roots seek out drain pipes.
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04
Dig the trench
Building America calls for a trench at least 22 inches deep and 14 inches wide, with the pipe 18 inches or more below the surface. Trenchers often cut too narrow, so widen by hand where needed.
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05
Line it with fabric
Lay 8-ounce landscape filter fabric wide enough to lap over both sides of the trench once it is filled.
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06
Add the base rock
Spread 4 inches of clean rock, 3/4 inch to 2 inches in size, and shape it so the pipe will keep a steady fall.
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07
Lay the pipe holes down
Use 4-inch perforated pipe with the holes facing down. Smooth, non-corrugated pipe is preferred because corrugated pipe collects sediment and clogs; a pipe with a factory filter sock is an alternative.
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08
Cover the pipe
Add 4 to 6 inches of clean rock over the pipe, then fold the fabric over the top and lap the edges.
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09
Finish the surface
Cover with 9 inches or more of rock, stone, topsoil or mulch. Avoid planting shrubs or trees over the line.
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10
Protect the outlet
Where the pipe daylights, end it on sloping ground with a splash block or stones to stop erosion.
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11
Test it
Run a garden hose into the high end and watch the outlet. Water should arrive steadily, with no pooling along the way.
If you have nowhere to drain to
Building America describes a basic dry well as a pit about 4 by 4 feet and 4 to 6 feet deep, lined with filter fabric and filled with clean 3/4 to 1 1/2 inch rock, with the drain pipe entering at half height or higher and at least 8 inches of soil on top. Check first that your soil can take the water: Nebraska Extension recommends a soil percolation test and warns against infiltration features where groundwater is shallow. A dry well in heavy clay simply fills up and stays full.
Drainage, neighbors and local rules
Moving water is regulated, and the rules differ widely between states, counties, towns and homeowners associations. Before you build:
- Check the outlet is legal. Most municipalities prohibit draining stormwater into the sanitary sewer, and connecting to a storm sewer or street gutter may need a permit.
- Keep the water on your side. Delaware's guidance asks owners to make sure a French drain will not cause flooding or pooling on neighboring properties, and Nebraska Extension advises checking that changes do not direct runoff toward neighbors.
- Ask about retention. Many jurisdictions require stormwater to be held or soaked in on your own lot.
- Deep or complex drains need a pro. Delaware notes that deeper, more complex drains and drains close to the foundation need a drainage contractor.
Delaware also warns that a French drain is not meant for serious flooding, is not recommended for yards that flood often because they lack slope, and, if poorly designed, can even raise the risk of floodwater reaching the foundation.
French drain maintenance and signs it is failing
Delaware suggests a monthly check to clear debris, leaf litter and rodent nests from the outlet, and a yearly check that the drain still works. The best test is free: watch the outlet during a heavy rain.
| What you notice | Likely cause | What to do |
|---|---|---|
| Outlet dry during a downpour while the yard is soggy | Pipe clogged with silt or roots, or a blocked outlet | Clear the outlet, then flush the pipe with a hose from the high end |
| Wet strip or puddles along the trench line | Gravel clogged with soil, or the fabric missing or torn | The top section may need digging out and rebuilding with clean rock |
| Water backing up at a low point | A sag in the pipe | Re-lay that section with a steady fall |
| Sinkholes or dips over the trench | Soil washing into the drain | Dig out, check the fabric and rebuild |
| Mud fan or gully at the outlet | Erosion where the pipe daylights | Add a splash block or stones |
| Roots in the outlet | Trees or shrubs planted too close | Clear the roots; move plants away from the line |
Before digging anything up, a drainage contractor can run a camera through the pipe to find the clog or sag. When you hire one, ask where the outlet will be and whether it is allowed, what pipe, fabric and rock they will use, and whether they will test the fall with water before backfilling.
French drain: frequently asked questions
What is a French drain?
A trench lined with filter fabric, filled with gravel and fitted with a perforated pipe. It collects water from wet ground and carries it to a lower outlet.
How deep should a French drain be?
Simple yard drains run about 8 to 24 inches deep. DOE's specification for drains protecting a house is a trench at least 22 inches deep, with the pipe 18 inches or more below the surface.
Which way do the holes go in a French drain?
Holes face down. Water rises into the pipe from the gravel below and flows away along the bottom.
Does a French drain need fabric?
Yes. Filter fabric around the gravel keeps soil out, and without it the gravel and pipe slowly clog.
Where should a French drain empty?
Somewhere lower than the whole drain: a swale, ditch, dry well, a lower part of your lot or a storm sewer where your town allows it.
Is a swale better than a French drain?
For surface runoff crossing a yard, a swale is simpler and easier to maintain. For soggy ground or tight side yards, a French drain works better.
Will a French drain fix a wet basement?
Often not on its own. Fix gutters, downspouts and grading first; water coming through the basement floor needs interior drainage to a sump pump.
Sources
Official and university guidance, checked on 27 October 2026.
- US DOE Building America Solution Center · Stormwater control: swales, drains and site grading ↗French drain trench size, fabric, rock, pipe and cover; swale shape and slopes; dry well construction; outlets; local ordinances.
- US DOE Building America Solution Center · Final grade slopes away from foundation ↗ENERGY STAR and IRC grading slopes within 10 feet of the house.
- Delaware DNREC I-ADAPT · French drain for yard ↗Definition, 8 to 24 inch DIY depth, limits for basements and floods, neighbors, permits, 811, monthly and yearly maintenance.
- University of Nebraska–Lincoln Extension · Disconnecting downspouts and impervious surfaces (G2186) ↗5-foot downspout extensions, rain gardens, dry wells, neighbors, sanitary sewer, septic setback, soil testing, calling 811.
- Common Ground Alliance · 811 for homeowners ↗Notice a few days before digging, waiting for all utilities, 18 to 24 inch clearance from marks, re-marks.
Puddles after every storm?
Walk the yard in the next heavy rain, note where water comes from and where it could go, and call 811 before you pick up a shovel.