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

At a glance

Building permit

Required unless the project fits a listed exemption; issued by PDS¹

Zoning

Yes, the Unified Development Code governs building and land development in unincorporated areas³

Septic permit

Health Department reviews most residential systems; state review starts at 3,500 gallons per day⁴

Rural water and sanitation

An approved well and approved on-site septic system may serve a rural home⁶

RV as primary residence

Prohibited; allowed only as temporary living quarters in specific zones, with day limits⁵⁷

Residential permit fees

$150 base application fee plus a 3% technology surcharge, $6.50 state surcharge and valuation-based plan-check fees⁸

Owner-builder

An owner may qualify for a contractor-registration exemption, but building and trade permits still apply⁹

Septic-friendly soils

Only 0.4% of soils have no severe limits for a conventional drainfield¹⁰

Who to call

Contact details are copied from each office’s official page and were checked against it on October 10, 2026.

Do you need a building permit 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 permits⁹¹².

Who is the Snohomish County building department, and how do you reach them?

Snohomish County Planning and Development Services (PDS) is the building department for unincorporated areas, and its main line is 425-388-3311¹³. PDS's office is at 3000 Rockefeller Avenue, 2nd Floor, Admin Building, Everett, Washington¹³. PDS runs the online PDS Permit Portal for applications and status tracking¹³. 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 completed¹⁴. For a residential permit, the signed final inspection card is the Certificate of Occupancy¹⁵.

Does Snohomish County have zoning?

Yes. Snohomish County's Unified Development Code regulates building and land development in unincorporated Snohomish County; incorporated cities administer their own zoning³¹⁶. The county's use matrix identifies permitted, conditional and prohibited uses by district¹⁷. 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^18192021. 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 model²². PDS also lists attached and detached accessory dwelling units, manufactured homes and temporary dwellings among its residential permit categories²³. We could not confirm a countywide minimum dwelling size, so ask PDS about the parcel and proposed unit¹³.

How do septic permits work in Snohomish County?

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.org²⁴. 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 permit²⁵. 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 utilities²⁶. 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 it²⁷²⁸. Septic permit fees vary by application and system and are listed in the Health Department's online fee schedule²⁹. 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.

Can you live in an RV or tiny home on your land in Snohomish County?

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 zones⁵⁷. 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 exceptions³⁰. 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 requirements²². 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 PDS²²¹³.

How do you build a home in Snohomish County, step by step?

1. Confirm the parcel's zoning district, setbacks, height and lot-coverage limits, plus any critical-area, floodplain or shoreline constraints, with PDS^3192021.
2. Secure Health Department water-and-sewer approval documentation; a rural home with plumbing needs an approved well and approved septic system²⁶²⁵.
3. For an individual well, obtain Health Department site review before construction, then follow state well-construction requirements and use a licensed driller³¹.
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 permission³²³³.
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 paid³⁴.
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^14353615.

What should you check before buying land in Snohomish County?

Check the parcel's zoning district with PDS first, because district rules control uses and dimensional standards¹³³⁷. 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 documentation¹⁰²⁶. 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 water³¹. If the home requires a Flood Hazard permit, that permit must be completed before final residential approval, and RV rules tighten inside a floodway³⁶³⁰. Confirm driveway access early: a county-road approach requires county permission, while a state-highway approach needs separate state permission³⁸³³. Snohomish County's effective property tax rate is about 0.8%, with a median annual bill near $5,121³⁹⁴⁰.

Watch-outs

• Do not assume a small structure is permit-free: Snohomish County's listed exemptions depend on the structure's use, zoning and dimensions, and property-line and environmental rules still apply¹.
• A recreational vehicle cannot be a primary residence in unincorporated Snohomish County, and even as temporary living quarters it's allowed only in specific zones with strict day limits and tighter floodway rules, so don't assume you can live in an RV on a parcel until you've confirmed its zone and use with PDS⁵⁷.
• A code-compliant tiny house is permitted as a single-family dwelling in six named unincorporated zones, but that rule does not cover other zones, RVs or park models; confirm the parcel and unit classification with PDS²²¹³.

Sources

1. Residential Building Permits, quoted and re-checked
2. Inspections, quoted and re-checked
3. Codes & Regulations, quoted and re-checked
4. Septic Permitting, quoted and re-checked
5. Assistance Bulletin #53 — Recreational Vehicles, quoted and re-checked
6. Sewer & Water Requirements, quoted and re-checked
7. Assistance Bulletin #53 — Recreational Vehicles, quoted and re-checked
8. Residential Building Permit Fees (New Construction & Remodels), Assistance Bulletin #18, quoted and re-checked
9. RCW 18.27.090 Exemptions, quoted and re-checked
10. Share of soils USDA rates "not limited" for a conventional septic drain field (SSURGO). A strict rating: the median county is about 6% and a tenth of counties are 0%, so a low figure means most lots need a site evaluation or an engineered system, not that septic is impossible. Cite it only with that caveat: Bolthole Index county data
11. Building Construction Codes, quoted and re-checked
12. RCW 18.27.090 Exemptions, quoted and re-checked
13. Snohomish County Planning and Development Services (PDS) (snohomishcountywa.gov)
14. Inspections, quoted and re-checked
15. PDS Building Inspection FAQs, quoted and re-checked
16. Planning & Development Services FAQs, quoted and re-checked
17. Planning and Development Services FAQs, quoted and re-checked
18. SCC Title 30, quoted and re-checked
19. SCC Title 30, quoted and re-checked
20. SCC Title 30, quoted and re-checked
21. SCC Title 30, quoted and re-checked
22. 30.22.120 Other Zone Categories Use Matrix, quoted and re-checked
23. Residential Building Permits, quoted and re-checked
24. Snohomish County Health Department – Environmental Health Division (snohd.org)
25. Sewer & Water Requirements, quoted and re-checked
26. Residential Building Permits, quoted and re-checked
27. Septic Permit Steps, quoted and re-checked
28. Septic Permit Steps, quoted and re-checked
29. Septic Permit Steps, quoted and re-checked
30. Assistance Bulletin #53 — Recreational Vehicles, quoted and re-checked
31. Well Site Applications & Review, quoted and re-checked
32. Snohomish County right-of-way permits (Public Works Customer Service Center / PDS) (snohomishcountywa.gov)
33. RCW 47.32.150 — Approach roads, other appurtenances—Permit (Washington statewide rule), quoted and re-checked
34. Residential Building Permits, quoted and re-checked
35. Inspections, quoted and re-checked
36. Inspections, quoted and re-checked
37. Snohomish County Code Title 30, quoted and re-checked
38. RCW 36.75.130 — Approaches to county roads—Rules regarding construction—Penalty (Washington statewide rule), quoted and re-checked
39. Effective property tax rate: Bolthole Index county data
40. Median property tax bill: Bolthole Index county data

Written October 10, 2026 from the rules quoted below, each taken from an official source and re-checked by an independent reviewer. This is research, not legal advice: rules change, so confirm with the office before you buy or build.