What Drainage Work Costs in Seattle, WA
Planning ranges for every drainage job, what pushes them up or down, and how to tell a fair quote from an inflated one — written for homeowners staring at a wet basement.
The Short Version
| Job | Typical range* | When it applies |
|---|---|---|
| Downspout tie-in / redirect | $300 – $2,000 | Roof water dumping at the foundation — cheapest high-impact fix |
| Yard French drain | $2,500 – $8,000 | Standing water, soggy lawn, a wet low spot |
| Exterior footing drain | $6,000 – $15,000+ | Failed clay tile; water at the foundation, yard accessible |
| Interior perimeter drain + sump | $6,000 – $15,000 | Wet finished basement — the standard Seattle fix |
| Sump pump (install / replace) | $1,200 – $4,000 | New basin + pump; battery backup adds ~$600–1,500 |
| Curtain / interception drain | $4,000 – $12,000 | Hillside lot, water arriving from uphill |
| Full basement waterproofing system | $10,000 – $20,000+ | Perimeter drain, sump, backup, wall treatment together |
*Planning ranges from regional drainage-industry norms — not a quote. Seattle jobs vary with length, depth, access, exit point, and what an assessment finds. Every real number starts with someone looking at your property.
What Moves the Number in Seattle Specifically
Where the water can exit
The single biggest driver. A lot that falls away to a daylight exit is the cheap case — gravity does the work. A flat lot with no downhill needs a sump, and a storm-system tie-in (where the city allows it) adds permit and connection cost. Same drain, very different price, decided by grade.
Length and depth of the run
Drainage is priced heavily per foot, and depth compounds it. A footing drain around a full foundation on a deep Seattle basement is a different project than a 30-foot yard drain.
What's on top of the dig
A run under open lawn is cheap to reach and restore. The same run under a driveway, a patio, mature landscaping, or a retaining wall costs more to excavate and much more to put back. Interior systems avoid this — one reason they're often chosen for finished Seattle basements over exterior digs.
Access for equipment
Seattle's narrow lots, alley-only access, and steep driveways can force hand-digging where a machine can't reach — slower and costlier. It's a real factor here that flatter, more open markets don't face.
What the old system left behind
Failed clay tile, roots, and buried surprises add time. Homes from the pre-1980 stock often hide an abandoned drain or an unexpected footing depth that the assessment catches and the quote should account for.
How to Read a Fair Quote
- It names the exit. A quote that doesn't say where the water ends up — daylight, storm, or sump — isn't a finished design. Ask.
- It checks the cheap fixes first. A contractor who looks at your downspouts and grade before quoting a $12,000 dig is thinking about your problem, not their invoice.
- It specifies materials. Filter fabric, clean drain rock, and pipe size matter enormously in our silty soils. "We'll put in a drain" is not a spec.
- It includes any needed permit. Storm tie-ins and work near Seattle's regulated steep-slope and critical areas can require permits. A bid that quietly skips one isn't cheaper — it's incomplete.
- It survives a second opinion. On any job over a few thousand dollars, a second assessment is worth the short wait. Good contractors expect it.