What it actually is
A French drain is a perforated pipe, buried in a trench, surrounded by gravel, wrapped in fabric, and graded to move water from one place to another by gravity.
That's it. The name doesn't refer to France. It comes from Henry French, a Massachusetts farmer and judge who wrote a book about agricultural drainage in 1859. The technique he popularized hasn't changed much in 150 years because it works.
What problem it solves
A French drain solves one specific problem: there's water somewhere it shouldn't be, and it needs to go somewhere else.
That sounds obvious, but the reason it matters is that most water problems around a home aren't really gutter problems. Gutters move water off the roof. Once water hits the ground, gutters can't help.
If you have:
- Standing water against the foundation after a storm
- A wet basement or crawlspace
- A soggy yard that takes days to dry out
- Water seeping into a garage from the driveway side
- A retaining wall that's getting hydrostatic pressure on the back side
You don't have a gutter problem, you have a ground-water problem. A French drain is the most reliable way to fix it.
How it works
The trench is dug to a depth that depends on the job. Typically 18 to 24 inches for foundation drainage, deeper for some applications.
The trench is graded with a continuous slope toward an outlet. Standard practice is at least 1 inch of fall per 10 feet of run. Less than that and the system stops moving water reliably.
Non-woven filter fabric goes in the trench first, lining the sides and bottom. Then a layer of washed gravel. Then the perforated pipe, holes pointing down. More gravel on top, fabric folded over to seal it, and soil on top of that.
Surface water and shallow groundwater move through the soil into the gravel. From the gravel, it enters the pipe through the perforations. From the pipe, it travels by gravity to the outlet.
Where the water actually goes
This is the part most DIY French drain articles skip, and it's the part that matters.
The outlet has to be lower than the input. The outlet has to be somewhere the water can actually go. And the outlet has to stay clear of debris.
Common outlets:
- Daylight, meaning the pipe surfaces at a low spot in the yard, the curb, or the back fence line
- A pop-up emitter, which is a spring-loaded cap that opens under water pressure
- A municipal storm tie-in, where allowed by code
Outlets that don't work:
- Dry wells in our heavy Oklahoma clay almost always fail within a few years
- Blind ends are not real outlets, full stop
- Tying into a sanitary sewer is illegal in most jurisdictions, including OKC
Sizing the outlet correctly is at least as important as sizing the trench.
When you don't need one
A French drain is a real piece of infrastructure with real cost. It's not the answer to every water problem.
Sometimes the fix is simpler:
- Downspout extensions: a lot of foundation puddling is just from the downspout dumping water two feet from the house. A 6 to 10 foot extension to a splash block solves the problem for $50 in materials.
- Regrading: if the soil slopes toward the foundation, no drain in the world will fully fix that. Sometimes the fix is to bring in dirt and reslope the bed.
- Yard drains: if the issue is a single low spot in the lawn that holds water, a small basin and a 4-inch line out to daylight is faster and cheaper than a full French drain.
When we walk a property, we're trying to solve the cheapest possible problem first. A real French drain comes in when the simpler fixes won't get there.
What a real install looks like
Some details that separate a French drain that lasts 30 years from one that fails in 3:
Washed gravel, not native fill. Native soil clogs the pipe perforations within months. Washed gravel keeps the system permeable forever.
Non-woven filter fabric. Woven fabric clogs faster. Non-woven keeps fines out without restricting flow.
Sized pipe. 4-inch is the residential default. We size up to 6-inch on jobs with a lot of contributing area.
Continuous slope. Sounds basic. We've inspected dozens of failed French drains where the slope was reversed mid-run because nobody verified it with a level. The drain becomes a buried bathtub.
Outlet to daylight. If we can't get to daylight, we use a pop-up. We don't terminate to a dry well in OKC clay unless we're confident the soil will actually accept the volume.
If you're seeing standing water around your home and you've already tried downspout extensions, have us walk the property. We'll tell you whether a French drain is the right fix and what it'll cost.
