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French Drain Installation in Seattle, WA

The gravel-and-pipe channel that gives trapped groundwater somewhere to go — before it reaches your foundation or pools in your yard.

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What a French Drain Actually Is

A French drain is simple in principle: a trench, a bed of gravel, and a perforated pipe wrapped in filter fabric, sloped so that water entering anywhere along its length runs to a low exit. Water follows the path of least resistance — the open gravel and pipe — instead of soaking into the ground next to your house. In Seattle's clay and glacial till, where the soil itself won't drain, that engineered path is the whole point.

The name covers several jobs that solve different versions of the same problem, and matching the right one to your situation is most of getting it right.

Exterior / footing French drain

Installed along the outside of the foundation at footing depth, it intercepts groundwater before it can bank up against the wall and push through. This is the classic fix for a basement that weeps at the base of the walls, and on older Seattle homes it often replaces a failed or root-clogged clay-tile system.

Yard French drain

A shallower run through the lawn or beds, collecting surface and near-surface water from a low spot, a spring, or a slope, and carrying it to daylight or the storm system. This is the fix for the corner of the yard that stays a swamp until May.

Curtain (interception) drain

Placed uphill of the house across the slope, it cuts off water coming down toward the foundation before it arrives. On Seattle's many hillside lots, a curtain drain often does more than any amount of work at the house itself.

Where the Water Goes — the Part That Sets the Price

A French drain only works if the water it collects has somewhere to exit, and that exit is the single biggest factor in cost and design:

A drainage specialist figures out the exit first, because it decides everything downstream. A contractor who quotes a French drain without telling you where the water ends up hasn't finished the design.

What Installation Looks Like

  1. Assess and locate. Walk the site, find the water source and the low exit, check grade and utilities, and settle on which drain type fits.
  2. Excavate. Trench to depth along the planned run — footing depth for a foundation drain, shallower for yard work.
  3. Bed and pipe. Filter fabric, drain rock, perforated pipe set to slope, then more rock — built so soil fines can't clog the pipe.
  4. Exit and connect. Run to daylight, storm tie-in, or sump; add cleanouts so the line can be serviced later.
  5. Backfill and restore. Cover, compact, and put the surface back — sod, gravel, or hardscape.

A straightforward yard drain can be a one-day job; a full exterior foundation drain on a hillside lot is several. Either way, ask to see the slope and the exit before backfill — that's the part you can't inspect once it's buried.

The Seattle detail that matters: filter fabric and clean drain rock aren't optional here. Our fine glacial soils will silt up a bare pipe within a few seasons. A properly sleeved and fabric-wrapped drain is the difference between a system that lasts decades and one that clogs in three winters.

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