- Residential drainage installation in the Seattle Metro Area runs from approximately $2,500 for a basic French drain to $8,000+ for a full-property catch basin network.
- Mid-range French drains (50-100 linear feet for a specific drainage problem) typically run $3,000-$6,000 — the most common installation tier.
- Six cost drivers: linear feet of drain pipe, trenching depth and complexity, catch basin count, exit point engineering, site access, and soil conditions.
- Simple solutions ($500-$2,000) solve some problems through downspout routing, surface regrading, and small interventions without needing full system installation.
- Full drainage systems are warranted when standing water persists across multiple areas, foundation moisture is evident, or slope conditions create destructive flow paths.
- The cost of unaddressed drainage problems (lawn dieback, perennial loss, foundation issues, hardscape damage) typically exceeds drainage installation cost over a 5-year horizon.
- Dry-season installation (late summer through October) costs less than wet-season installation because dewatering isn't required.
Residential drainage installation in the Seattle Metro Area runs from approximately $2,500 for a basic French drain serving a single problem area to $8,000+ for a full-property catch basin network with multiple connected drainage systems. Simple solutions — downspout extensions, surface regrading, small catch basins — typically run $500-$2,000. Mid-range French drains (50-100 linear feet serving a specific drainage problem) run $3,000-$6,000. Full-property drainage systems with multiple catch basins, connected French drains, and engineered exit points run $6,000-$15,000+ depending on scope. The cost reflects substantial trenching, gravel backfill, perforated pipe, geotextile fabric, and proper daylighting to drainage exit points. Pacific Northwest clay soils and significant residential slopes make drainage one of the more common enhancement categories — the cost is real but solves problems that compound for years if left unaddressed.
What does typical drainage pricing look like?
Common residential drainage projects fall into a few cost tiers:
Simple solutions ($500-$2,000):
- Downspout extensions and routing adjustments
- Surface regrading for low spots
- Single small catch basin installation
- Splash block additions and minor grade work
These often combine with broader landscape enhancement projects rather than standing alone.
Mid-range French drains ($3,000-$6,000):
- 50-100 linear feet of perforated drain pipe in gravel-backfilled trench
- Geotextile fabric wrapping
- 1-2 catch basins as collection points
- Daylighted exit point to acceptable drainage location
- Site restoration after trenching
This is the most common drainage installation tier — addresses a specific saturation problem (chronic standing water in a low area, foundation moisture, slope-driven runoff) with focused infrastructure.
Full-property drainage systems ($6,000-$15,000+):
- Multiple connected French drains across the property
- Network of catch basins at key collection points
- Engineered exit point (storm drain connection where allowed, dry well, or daylighted exit)
- Integrated downspout management
- Substantial trenching and site work
This tier addresses properties with multiple drainage problems or properties where comprehensive drainage redesign is part of broader landscape work.
The drainage prep approach covers diagnostics that determine which tier of solution a property actually needs.
What drives the cost difference between drainage projects?
Six factors shape drainage installation pricing:
Linear feet of drain pipe. The most predictable cost driver. Each additional linear foot of French drain adds trenching, gravel, pipe, and labor. Drains routed under hardscape, around tree roots, or through tight site access cost more per linear foot than drains in open accessible areas.
Trenching depth and complexity. Standard drainage trenching runs 18-24 inches deep. Deeper installations (frost line considerations on higher elevations, deeper soil saturation issues) require more excavation. Hand-trenching where machine access is limited adds substantial cost.
Catch basin count. Each catch basin adds material plus installation labor. Simple drainage might use 1-2 catch basins; complex networks use 5-10+. Catch basin specifications (depth, grate type, connection complexity) also affect per-unit cost.
Exit point engineering. Connecting to municipal storm drains (where permitted) costs differently than installing a dry well; both differ from daylighting to a natural drainage route. Exit point selection depends on site conditions and local code requirements.
Site access and excavation conditions. Properties with truck-accessible drainage routes cost less than properties requiring hand-trenching around mature trees, through tight spaces, or under existing landscape installations.
Soil conditions and dewatering. Working in already-saturated soils (winter drainage work) requires dewatering and adds substantial cost. Dry-season drainage installation (late summer through October) costs less than wet-season work.
When does simple drainage solve the problem versus needing a system?
Many residential drainage problems can be solved with simple interventions rather than full system installation. The honest diagnostic:
Simple solutions work when:
- The problem traces to a single source (clogged grate, misrouted downspout, low spot in lawn)
- Surface flow patterns can be redirected through grading
- Saturation is seasonal but soil drains adequately between rain events
- The property has clear drainage exit potential through grading alone
Full drainage systems are needed when:
- Standing water persists for days after rain events
- Multiple problem areas across the property
- Soil clearly has poor drainage despite surface management
- Foundation moisture problems indicate subsurface saturation issues
- Slope conditions create destructive water flow paths
The right professional assessment distinguishes the two — many drainage consultations result in simple-solution recommendations rather than full system installation when the diagnosis supports the simpler approach. The drainage contractor selection guide covers how to evaluate the diagnostic conversation.
What's the cost of letting drainage problems continue?
Drainage problems left unaddressed in Pacific Northwest yards typically compound over time. Common downstream costs:
Lawn dieback and remediation. Standing water kills turf in patches; remediation typically runs $1,000-$3,000 per season for affected lawn areas. Repeat cost annually until drainage is addressed.
Perennial and shrub loss. Saturated soil kills plants over multiple seasons. Replacement cost varies but typically runs $500-$2,000 per affected bed area.
Foundation moisture and crawl space issues. Persistent foundation moisture leads to crawl space humidity, potential structural concerns, and possible mold remediation costs. These problems can run substantially higher than drainage installation cost.
Hardscape settling and damage. Patios and walkways installed on saturated subsoil settle and crack. Remediation typically costs more than original installation.
Tree health decline. Mature trees in chronically saturated soil decline over years. Tree removal and replacement costs run substantially higher than drainage prevention.
The honest math: drainage installation at $3,000-$8,000 usually costs less over a 5-year horizon than the cumulative remediation cost of leaving the underlying problem unaddressed. The broader costs and planning context covers how this long-horizon math applies across other landscape categories.
