Residential Drainage Design · Snohomish County
Residential drainage plans for Snohomish County building permits.
It's one of the most common calls the Arlington office gets: a homeowner's RBP — residential building permit — comes back conditioned on an engineered drainage plan, and nobody warned them a civil engineer would be part of building a house.
AXE packages residential drainage as a defined scope: confirm what the county actually requires, design the smallest system that passes, stamp it, and support the permit through review. Lake Stevens, Marysville, Stanwood, Snohomish, Camano-adjacent parcels — this bench works the county weekly.
Who this page is for
- Homeowners whose Snohomish County RBP requires a drainage plan
- Owner-builders on county acreage juggling LDA and building permits together
- Buyers evaluating lots in Lake Stevens, Marysville, or Stanwood where drainage feasibility matters
- Anyone with a wet, flat, or till-soil lot wondering what approval will take
What AXE handles
- Targeted drainage plans for single-family RBPs — the right scope for most homes
- Drainage design coordinated with LDA permits when county earthwork review applies
- Dispersion, infiltration, and detention solutions matched to county soils
- ADU and DADU drainage on existing developed lots
- Plain-English walkthroughs of county drainage letters
The local picture
Snohomish County frequently conditions residential permits on drainage when projects add hard surface, sit near critical areas, or shed water toward neighboring parcels. The county's targeted-plan scope covers most single-family situations — full plans are the exception, not the default.
Glacial till is everywhere in the county, which often rules out simple infiltration. The county's reviewers know it, and designs that pretend otherwise stall. We soil-check first and design what the ground can actually do.
Commonly served ZIP codes in this area: 98223 · 98258 · 98270 · 98290 · 98292
How it works, start to stamp.
01 · Read the requirement
Send us the county's correction letter or condition — we'll translate exactly what's being asked and what scope satisfies it.
02 · Lot assessment
Soils, slope, discharge path. Ten minutes of the right questions often saves thousands in over-design.
03 · Stamped plan
A residential-scale drainage plan formatted for the county's RBP file.
04 · Review handled
County questions route to us until the permit clears.
PE-licensed. Founded 2017. One engineer of record from feasibility through approval.
Questions we hear about residential drainage design in Snohomish County.
The county conditioned my building permit on a drainage plan. How long does this take?
Design typically runs a couple of weeks once soils information is in hand, and we issue a written proposal within one business day of your call so you know cost and schedule up front.
Do I need both an LDA permit and a drainage plan?
If your site work crosses the county's land-disturbance thresholds, yes — and they review together. We engineer both as one package so the grading and drainage never contradict each other.
My lot doesn't perk. Does that kill the project?
No — it moves the design from infiltration to dispersion or detention. Till lots get approved every week in this county; they just need the system designed for the soil that's actually there.
County letter in hand?
Forward it with your parcel number. We'll tell you exactly what it means and what it costs to clear — written proposal within one business day.
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