Drainage contractor —
Seattle & Puget Sound.
Most basement moisture problems are drainage problems. We grade away from foundations, install perimeter drains, and route stormwater to legal discharge points.
Most basement moisture problems are drainage problems, not waterproofing problems. We grade away from foundations, install perimeter drains, and route stormwater to legal discharge points (street, dry well, or detention). When drainage is right, waterproofing rarely fails.
Seattle gets 38 inches of rain annually, concentrated October through April. Roof, surface, and subsurface drainage need to handle that volume continuously — a single backed-up downspout can saturate a foundation in one storm.
What we build
SCOPE- 01French + foundation drains
- 02Sump pump installation
- 03Stormwater retention
- 04Grading + swales
- 05Downspout extension
- 06Permeable pavement options
Phased process
PROCESS- 01
Assessment
Identify water sources: roof, surface, groundwater. Test soil percolation. Map grades and discharge points.
- 02
Permit
Permit required for new stormwater connections, dry wells, or discharge to street.
- 03
Excavation
Trench for French drains, foundation perimeter drains, or storm pipe runs.
- 04
Pipe + filter
Perforated PVC drain tile wrapped in filter fabric and drain rock; solid PVC discharge lines to legal outfall.
- 05
Backfill + finish grade
Drain rock backfill, regraded surface to drain 6" in first 10 ft from foundation.
Spec sheet
SPEC- +4" perforated PVC drain tile (smooth interior, not corrugated black flex)
- +Filter fabric (Mirafi 140N or equivalent) wrapped around drain rock
- +Drain rock (1.25" minus) backfill
- +4" solid PVC discharge lines to legal outfall
- +Sump pump (Zoeller, Liberty) where gravity discharge isn't possible
- +Catch basins and trench drains for surface water
- +Dry well (StormChamber, Cultec) for stormwater retention
Cost drivers
COST- Linear footage$60–$120/lf for perimeter foundation drain installed
- Discharge type (gravity → pump → dry well)$0 gravity → $1,500 sump pump → $8K dry well
- Excavation depthFoundation drains require excavating to footing depth — $80–$200/lf for deep walls
- Hardscape demo + replacementDrainage under existing patio/driveway adds significant cost
Codes & permits
COMPLIANCE- Seattle SPU stormwater code
New impervious surface and drainage modifications often require stormwater permit and on-site retention.
- IRC R401.3
Foundation grading must drain 6" in first 10 ft away from house.
- Discharge points
Discharge to street, storm sewer, or approved dry well — never to neighbor's property or sidewalk surface.
Is drainage the right call?
- →Basement or crawlspace moisture — water on floor, efflorescence on walls
- →Surface ponding in yard after rain
- →Downspout discharge causing erosion or basement leaks
- →Pre-emptive on hillside lots before basement finish
Drainage questions
FAQQ.01
French drain vs foundation perimeter drain — what's the difference?
Foundation perimeter drain runs along the footing at the building exterior, captures subsurface water before it reaches the foundation. French drain is a generic term for any drain field collecting surface or subsurface water elsewhere on the property.Q.02
Do I need a sump pump?
Only when gravity discharge isn't possible — typically basements below street level or lots without slope to a legal outfall. Where gravity works, it's more reliable and zero-energy.Q.03
Can I tie my drainage to the city storm sewer?
Sometimes — depends on city, capacity, and your service connection. Seattle SPU has specific rules; we coordinate with the utility during permit.Q.04
Will drainage fix my wet basement?
Usually, yes — 80%+ of wet basements are exterior drainage problems, not foundation cracks. Fix grading, downspouts, and perimeter drain first; address foundation waterproofing only if water persists.
Official resources & sources
- Source ↗WA DOE Stormwater Manual for Western WA
- Source ↗WSEC 2021 Residential Energy CodeEnvelope, HVAC, hot-water and air-sealing requirements
- Source ↗WA HB 1110 — Middle housing lawStatewide middle-housing zoning preemption
- Source ↗WA HB 1337 — ADU statewide rulesTwo-ADU baseline, no owner occupancy, parking limits
- Source ↗WA Dept. of Commerce — ADU resources
- Source ↗WA L&I contractor license lookupVerify Golden State ADU Builders Inc · GOLDESA747LZ
- Source ↗Washington State Building Code CouncilStatewide adopted codes (IRC, IBC, WSEC)
Ready to scope your drainage project?
Send a paragraph and the address. A licensed PM replies within one business day with next steps.
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