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

At a glance

Building permit

Required for most residential construction, issued by PDS¹

Zoning

Yes, unincorporated areas are zoned under the county's Unified Development Code (Title 30)²⁶

Septic permit

Snohomish County Health Department does design approval, permits and inspections³

Owner-builder

Exempt from contractor registration when building on your own property⁷

RV as primary residence

Prohibited; allowed only as temporary living quarters in specific zones, with day limits⁵⁸

Residential permit fees

$150 base application fee plus a 3% technology surcharge, $6.50 state surcharge and valuation-based plan-check fees⁹

Federal land

48.5% of the county is federal land (national forest and wilderness)¹⁰

Septic-friendly soils

Only 0.4% of soils have no severe limits for a conventional drainfield⁴

Who to call

Contact details are copied from each office’s official page and were checked against it on September 25, 2026.

Do you need a building permit in Snohomish County, Washington?

Yes. Unincorporated Snohomish County requires a building permit for most residential construction, and Planning and Development Services (PDS) reviews and issues it¹. Washington's state building code, which PDS enforces locally, is built on the 2021 International Building Code with state amendments¹¹. State law does let a county opt in to a small exemption for minor Group R-3 or M-1 work worth $1,500 or less in any 12 months, but adoption is up to each county and this guide could not confirm whether Snohomish has adopted it, so assume a permit applies until PDS tells you otherwise¹². Residential permit fees in unincorporated Snohomish County start with a $150 base application fee, plus a $6.50 state surcharge and a 3% technology surcharge on top of plan-check and permit fees calculated from the county's valuation of the structure, and new single-family homes and duplexes add an 11% increase for mechanical and plumbing inspections⁹. One narrow statewide exemption is confirmed: temporary structures used solely to grow horticultural plants, such as hoop houses, are not treated as a building under the state building-code chapter¹³.

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 425-388-3311¹⁴. PDS's office is at 3000 Rockefeller Avenue, 2nd Floor, Admin Building, Everett, Washington¹⁴. PDS also runs the online PDS Permit Portal for applying and tracking permit status, and for zoning or land-use questions the staff directory routes inquiries through its AskPermitTech intake so the right planner responds¹⁴. The same department, not a separate zoning office, enforces the county's Unified Development Code (Title 30) in unincorporated Snohomish County²⁶.

Does Snohomish County have zoning?

Yes. Snohomish County zones all unincorporated land under its Unified Development Code, Title 30, adopted under the state Growth Management Act²⁶. The county's use matrix lists every zoning designation along with its permitted, conditionally permitted and non-permitted uses, and both minimum lot area and setback requirements from roads and other properties vary by zone, so PDS can tell you your parcel's district and its specific standards⁶¹⁵¹⁶. Cities within the county administer their own zoning inside city limits, so if your parcel falls within an incorporated city's boundary you'll need to contact that city rather than the county¹⁷. A wheeled tiny house up to 400 square feet is allowed statewide if it is built to the Washington State Building Code, but approval still depends on where it is sited, so PDS's local requirements for foundation, utilities and location control on your parcel¹⁸. Washington requires cities and counties to allow at least two accessory dwelling units on qualifying lots, but only inside a designated urban growth area; most rural land in unincorporated Snohomish County sits outside those boundaries, so that statewide ADU mandate does not reach it, and any ADU on rural land follows the county's own Title 30 rules instead¹⁹²⁶. Any dwelling built under the state building code must have at least 190 square feet of habitable space and at least one room of 120 square feet or more²⁰.

How do septic permits work in Snohomish County?

Septic is not a PDS function here: the Snohomish County Health Department's Environmental Health Division designs, permits and inspects on-site sewage systems (OSS), reachable at 425-339-5250 or [email protected]²¹³. Every residential building permit application in unincorporated Snohomish County must include Water and Sewer Approval from the Health Department, so line up your septic (or public sewer) approval before you submit your building permit application, not after²². Once your septic fee is paid and other requirements are met, the Health Department issues the installation permit, and your installer must have that permit in hand before starting any work²³. The system must stay uncovered until the Health Department completes a final inspection confirming the as-built matches the design, after which it signs off and the installer can cover it²⁴. Statewide, an OSS permit (other than a minor repair) must be obtained before construction begins, and the local health officer has up to 30 days to respond and can issue a permit valid for up to 5 years²⁵. Soils are the real constraint in this county: only 0.4% of Snohomish County's soils carry no severe limitation for a conventional septic drainfield, so most sites need a certified designer and likely an engineered or alternative system rather than a standard gravity drainfield⁴.

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 does allow one as temporary living quarters, and only in specific zones: RD, RRT-10, R-5, F, F&R, A-10, SA-1, RC and RU⁵⁸. Outside the floodway, a primary RV use is limited to one fully licensed, highway-ready RV per property for up to 180 days in any 12-month period, while an incidental use, meaning every RV on the property is owned by someone who already occupies a legally occupied dwelling there, has no limit on number or duration⁸. If a guest rather than a resident occupies the RV, that use is capped at 180 days in any 12-month period and one RV per lot, and RV storage itself is allowed only on a property permitted as an RV park⁸. Inside the floodway, rules tighten further: during flood season, October 1 through March 30, RV use is limited to day use only, from dawn to dusk, with narrow exceptions for incidental use, overnight guests of a legally occupied dwelling for 21 days or less, one farm-worker RV on the farm where they work for up to 180 days, and temporary overnight use of up to 180 days in a qualifying mobile home park that has operated continuously since at least 1970 with septic or sewer, water and other utilities and an approved RV flood evacuation plan on file²⁶. A wheeled tiny house up to 400 square feet can be built to the Washington State Building Code, but whether and where you can place one on a specific parcel is a local zoning and building question that PDS's district-by-district rules decide, and this guide could not confirm a Snohomish County-specific tiny-home occupancy rule beyond that state baseline¹⁸. Confirm your parcel's zoning district with PDS before you buy with an RV or tiny home in mind¹⁴.

Building a home in Snohomish County: the steps, in order

1. Confirm your parcel's zoning district and any critical-area, floodplain or shoreline overlays with PDS before you buy¹⁴².
2. Get a septic site evaluation, design and Water and Sewer Approval from the Snohomish County Health Department, since your building permit application must include that approval and a permit must be issued before installation begins²¹²²²³.
3. If your driveway will be new, PDS administers the Type D right-of-way permit for creating a driveway to a new home, currently listed at $350 per connection, while a separate Washington State Department of Transportation permit applies instead if the parcel fronts a state highway²⁷⁹²⁸.
4. Submit your building permit application, site plan and structural plans to PDS along with the $150 base application fee; projects over $5,000 must include the parcel's legal description or tax parcel number and contractor information¹⁴⁹²⁹.
5. If you are creating a new parcel rather than building on an existing one, know that any subdivision or short subdivision must meet chapter 58.17 RCW and the county's local subdivision regulations before PDS or the county can approve it³⁰.
6. Schedule inspections through PDS as construction proceeds, and keep your septic system uncovered until the Health Department's final inspection signs off on it¹⁴²⁴.

What to check before you buy land in Snohomish County

Check the parcel's zoning district with PDS first, since it decides what you can build, minimum lot standards, whether RV or tiny-home living is realistic and whether an ADU is possible on that specific lot¹⁴²⁸. Get an on-site sewage evaluation before you make an offer: across the county only 0.4% of soils carry no severe limitation for a conventional drainfield, so a raw-looking parcel can still need an expensive engineered septic system, and your building permit application will need Health Department water-and-sewer approval either way⁴²¹²². If any part of the property sits in a mapped floodplain, contact your local government, in this case PDS, for a floodplain development permit before you build, and know that RV rules tighten substantially inside a floodway³¹²⁶. Confirm driveway access early: a new approach onto a county road needs county board permission and currently runs $350 per connection, while one onto a state highway needs a separate WSDOT permit³²⁹²⁸. Snohomish County's effective property tax rate runs about 0.8%, with a median annual bill near $5,121, so budget property taxes into your holding costs³³³⁴. Finally, 48.5% of the county is federal land concentrated in the Cascades, and 83.1% of the county is wooded, so confirm your specific parcel's private, buildable acreage rather than assuming county-wide averages apply to it¹⁰³⁵.

Watch-outs

• This guide could not confirm whether Snohomish County has adopted Washington's optional $1,500 minor-work building-permit exemption (WAC 51-16-080); call PDS at 425-388-3311 before assuming a small project is exempt¹⁴¹².
• 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 PDS⁵⁸.
• This guide could not confirm Snohomish County's own tiny-home or manufactured-home occupancy rule beyond the statewide building-code baseline; confirm with PDS before you buy land planning for either¹⁴¹⁸.

Sources

1. Snohomish County PDS – Residential Building Permits (2026 county census)
2. Codes & Regulations (2026 county census)
3. Snohomish County Health Department – Septic Permitting (2026 county census)
4. Share of soils without severe limits for a conventional septic drain field (USDA SSURGO): Bolthole Index county data
5. Assistance Bulletin #53 — Recreational Vehicles, quoted and re-checked
6. Planning & Development Services FAQs, quoted and re-checked
7. Washington State Legislature - RCW 18.27.090 Exemptions (2026 county census)
8. Assistance Bulletin #53 — Recreational Vehicles, quoted and re-checked
9. Residential Building Permit Fees (New Construction & Remodels), Assistance Bulletin #18, quoted and re-checked
10. Federal land share: Bolthole Index county data
11. RCW 19.27.031 — State building code—Adoption—Conflicts—Opinions (Washington statewide rule), quoted and re-checked
12. WAC 51-16-080 — Permit exemptions guideline (Washington statewide rule), quoted and re-checked
13. RCW 19.27.065 — Exemption—Temporary growing structures used for production of horticultural plants (Washington statewide rule), quoted and re-checked
14. Snohomish County Planning and Development Services (PDS) (snohomishcountywa.gov)
15. Planning & Development Services FAQs, quoted and re-checked
16. Planning & Development Services FAQs, quoted and re-checked
17. Planning & Development Services FAQs, quoted and re-checked
18. Tiny Houses (Washington statewide rule), quoted and re-checked
19. RCW 36.70A.680 — Accessory dwelling units—Local regulation (Washington statewide rule), quoted and re-checked
20. WAC 51-50-1208 — Section 1208—Interior space dimensions (Washington statewide rule), quoted and re-checked
21. Snohomish County Health Department – Environmental Health Division (snohd.org)
22. Residential Building Permits, quoted and re-checked
23. Septic Permit Steps, quoted and re-checked
24. Septic Permit Steps, quoted and re-checked
25. WAC 246-272A-0200 Permit requirements (Washington statewide rule), quoted and re-checked
26. Assistance Bulletin #53 — Recreational Vehicles, quoted and re-checked
27. Snohomish County right-of-way permits (Public Works Customer Service Center / PDS) (snohomishcountywa.gov)
28. RCW 47.32.150 — Approach roads, other appurtenances—Permit (Washington statewide rule), quoted and re-checked
29. RCW 19.27.095 — Building permit application—Consideration—Requirements (Washington statewide rule), quoted and re-checked
30. RCW 58.17.030 — Subdivisions to comply with chapter, local regulations (Washington statewide rule), quoted and re-checked
31. Planning & regulation — Washington State Department of Ecology (Washington statewide rule), quoted and re-checked
32. RCW 36.75.130 — Approaches to county roads—Rules regarding construction—Penalty (Washington statewide rule), quoted and re-checked
33. Effective property tax rate: Bolthole Index county data
34. Median property tax bill: Bolthole Index county data
35. Wooded share of land: Bolthole Index county data

Written September 25, 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.