Building permits, zoning and land rules in Snohomish County, Washington

Yes. Most residential structures in unincorporated Snohomish County require a building permit¹. Listed exceptions include non-habitable structures smaller than 400 square feet in rural zones, non-habitable structures smaller than 200 square feet in urban zones, and uncovered decks no more than 30 inches above grade; exempt work must still meet property-line and environmental rules¹. Snohomish County uses the 2021 building-code editions as amended and adopted by Washington¹¹. Residential permit fees start with a $150 base application fee, plus a $6.50 state surcharge and a 3% technology surcharge; plan-check and permit fees depend on county valuation, and new single-family homes and duplexes add 11% for mechanical and plumbing inspections⁸. Washington's owner-builder and agricultural exemptions concern contractor registration, not county building, land-use, septic or trade permits⁹.

Snohomish County Planning and Development Services (PDS) is the building department for unincorporated areas, and its main line is 425-388-3311¹². PDS's office is at 3000 Rockefeller Avenue, 2nd Floor, Admin Building, Everett, Washington¹². PDS runs the online PDS Permit Portal for applications and status tracking¹². PDS also handles inspections for permits in unincorporated Snohomish County². Before a residential final inspection can be scheduled, all conditions must be met, outstanding fees paid and applicable related permits completed¹³. For a residential permit, the signed final inspection card is the Certificate of Occupancy¹⁴.

Yes. Snohomish County's Unified Development Code regulates building and land development in unincorporated Snohomish County; incorporated cities administer their own zoning^3,15. The county's use matrix identifies permitted, conditional and prohibited uses by district¹⁵. Its bulk matrix sets district-specific minimum lot area, lot width, road and property-line setbacks, maximum building height and maximum lot coverage, with notes and exceptions that can change the answer for a parcel^15,16. A code-compliant tiny house used as a single-family dwelling is permitted in the SA-1, RC, RU, R-20,000, R-12,500 and WFB zones, but this does not answer siting in other zones or cover an RV or park model¹⁷. PDS also lists attached and detached accessory dwelling units, manufactured homes and temporary dwellings among its residential permit categories¹. We could not confirm a countywide minimum dwelling size, so ask PDS about the parcel and proposed unit¹².

The Snohomish County Health Department reviews residential and small-business septic systems with design flows below 3,500 gallons per day; the Washington State Department of Health handles systems at or above 3,500 gallons per day⁴. The county office is reachable at 425-339-5250 or SHD-EHQ@snoco.org⁴. A rural residence or building with plumbing needs an approved well and approved on-site septic system, and an existing septic system needs Health Department approval before the county issues the building permit⁶. Every residential permit application in unincorporated Snohomish County must include Health Department water-and-sewer approval documentation, but that requirement does not mean every parcel must connect to public utilities¹. The installer must leave the septic system uncovered while the designer reviews the work and submits the as-built record; the Health Department then performs the final inspection and, if the as-built record is accurate, signs the permit so the installer can cover it¹⁸. Septic permit fees vary by application and system and are listed in the Health Department's online fee schedule¹⁸. Only 0.4% of Snohomish County soils have no severe limitation for a conventional drainfield, so obtain a site evaluation before relying on a standard system¹⁰.

A recreational vehicle cannot be your primary residence in unincorporated Snohomish County, but the county allows temporary living quarters in the RD, RRT-10, R-5, F, F&R, A-10, SA-1, RC and RU zones^5,7. Outside the floodway, primary RV use is limited to one fully licensed, highway-ready RV per property for up to 180 days in any 12-month period; guest occupancy has the same duration and one-RV limit⁷. During flood season, RV use in a floodway is generally limited to day use, with narrow exceptions⁵. A tiny house is different: a dwelling of no more than 400 square feet, excluding sleeping lofts, may be used as a single-family dwelling in the SA-1, RC, RU, R-20,000, R-12,500 and WFB zones if it meets state-code standards, including ceiling-height and ventilation requirements¹⁷. That rule does not establish permission in other zones or apply to an RV or park model, so confirm the unit's legal classification and parcel zoning with PDS^12,17.

1. Confirm the parcel's zoning district, setbacks, height and lot-coverage limits, plus any critical-area, floodplain or shoreline constraints, with PDS^3,15,16.
2. Secure Health Department water-and-sewer approval documentation; a rural home with plumbing needs an approved well and approved septic system^1,6.
3. For an individual well, obtain Health Department site review before construction, then follow state well-construction requirements and use a licensed driller¹⁹.
4. Resolve access: PDS handles the Type D right-of-way permit for a driveway to a new home, while a state-highway approach requires state permission^20,21.
5. Submit the residential checklist, structural plan, site plan, drainage plan and water-and-sewer approval; final inspection also requires associated permits to be complete and outstanding fees paid².
6. Request inspections as work proceeds. Complete applicable driveway, access, culvert and Flood Hazard permits before final approval, then retain the signed residential final-inspection card as the Certificate of Occupancy^2,13,14.

Check the parcel's zoning district with PDS first, because district rules control uses and dimensional standards^12,22. Get an on-site sewage evaluation before making an offer: only 0.4% of county soils have no severe limitation for a conventional drainfield, and a residential permit application needs Health Department water-and-sewer approval documentation^1,10. If the parcel needs a private well, the Health Department reviews whether the proposed site is suitable before construction; that approval is not permission to start drilling or draw water¹⁹. If the home requires a Flood Hazard permit, that permit must be completed before final residential approval, and RV rules tighten inside a floodway^2,5. Confirm driveway access early: a county-road approach requires county permission, while a state-highway approach needs separate state permission^21,23. Snohomish County's effective property tax rate is about 0.8%, with a median annual bill near $5,121¹⁰.