ADU Pass
Arlington
ADU Pass helps homeowners in Arlington, Snohomish County, Washington navigate the permit paperwork for building an accessory dwelling unit. This area covers 1 ZIP code.
Map
ADU details
ADU legality: allowed
Washington preempts most local ADU restrictions. Arlington permits ADUs by right in single-family zones per its zoning ordinance.
Cost scenarios
| Scenario | Sq ft | Permit | Build | Total |
|---|---|---|---|---|
| minimum | 150 | $2,900 | $48,750 | $51,650 |
| 600 | 600 | $2,900 | $195,000 | $197,900 |
| midpoint | 675 | $2,900 | $219,375 | $222,275 |
| maximum | 1,200 | $2,900 | $390,000 | $392,900 |
Fee breakdown (as of 2026-04)
Permitting process
- Pre-application zoning and overlay verification (~5d)
Confirm zoning eligibility under updated AMC residential chapters (post-EHB 1337). Critical: verify Arlington Municipal Airport (KAWO / AWO) AICUZ overlay - parcels in APZ-1, APZ-2, or 65+ DNL noise contours have additional restrictions. Check Stillaguamish River floodway and critical areas. - Pre-application meeting with Community & Economic Development (~14d)
Optional but recommended pre-application meeting with CED staff. Review SEPA threshold (typically below threshold for single ADU), critical area consultation if Stillaguamish floodway proximity, and zoning permit pathway selection. - Submit through Arlington Citizen Portal (CivicGov) (~1d)
Apply online at civicgov4.com/wa_arlington/portal. Choose Building and Fire Permits track for the ADU. Upload site plan, floor plans, elevations, structural calcs, WSEC 2021 energy compliance, SEPA checklist if required, and Zoning Permit Application Packet. - Intake completeness check (~7d)
CED reviews submittal for completeness; routes to Planning, Building, Public Works, and Arlington Fire concurrent review. - Concurrent plan review (planning, building, public works, fire) (~28d)
Planning reviews zoning conformance and AICUZ overlay if applicable. Building reviews IRC 2021 with Washington amendments. Public Works reviews stormwater (Ecology Western WA Manual), driveway, water/sewer connections. Arlington Fire reviews access. Typical 2 cycles. - Permit issuance and fee payment (~3d)
Pay building permit fees, plan-review fees, water/sewer system development charges, Snohomish County PUD electrical service charges (separate utility), and Washington State Building Code Council surcharge. - Construction inspections via Citizen Portal
Footing, foundation, framing, mechanical/plumbing/electrical rough, insulation, drywall, final. Schedule via portal or call CED inspections line. - Certificate of occupancy (~5d)
Final inspection sign-off triggers CO; ADU eligible for occupancy and rental.
Viability (permitted uses)
- Long-term rental: yes Long-term rental of ADU explicitly permitted; Washington owner-occupancy preemption (where applicable) makes ADU eligible for full landlord-tenant treatment.
- Short-term rental: with-restrictions STR rules vary by city. Arlington regulates STRs separately from ADU permitting; check local STR ordinance and HOA covenants.
- Office rental: with-restrictions Detached office rental requires home occupation permit or rezoning.
- Home office: yes Home occupation permitted with restrictions on signage and customer traffic.
- Studio / workshop: yes Personal artist studio is a permitted accessory use.
- Agriculture: with-restrictions Limited urban agriculture permitted in residential zones; livestock varies by district.
- Relative support: yes Family-occupancy ADU explicitly permitted in single-family zones.
Contacts
Staff: Building Services Division (Building permit intake and inspections), Snohomish County PUD No. 1 - New Service (Electrical service for ADUs (separate utility)), Arlington Fire Department (Fire access and Knox box review)
Utilities
- Water: Arlington Water Utility · 21d connect · $4,500
- Sewer: Arlington Sewer / Wastewater · 21d connect · $5,500
- Electric: Arlington Electric Utility · 14d connect · $1,800
- Gas: Arlington Gas Utility · 21d connect · $1,500
Property values & taxes
Construction timeline
Realistic total: best 7mo · typical 11mo · worst 17mo
Financing
State ADU loans:
Insurance impact
HOA prevalence & preemption
Washington enacted HOA preemption of ADU bans in Substitute House Bill 1337 (2023), which amended the Washington Uniform Common Interest Ownership Act and the Washington Horizontal Property Regimes Act to prohibit common-interest communities from banning ADUs on lots in GMA-planning jurisdictions. A homeowners' association may impose reasonable aesthetic or architectural standards, but may not categorically prohibit ADUs.
Regulatory overlays (1)
- seismic-zone
Seismic Design Category D1 per ASCE 7; soft-story and unreinforced-masonry seismic considerations may apply.
Technical envelope (climate & building code)
Climate & energy code
Building code
Amendments:
- Amendment
- Amendment
Legal history (timeline)
Current ordinance: Arlington Municipal Code residential chapters - Accessory Dwelling Units (post-EHB 1337 conformance), adopted 2018-04-02, last amended 2025-06-30
- 2018-04-02 — Arlington Comprehensive Plan periodic update with ADU provisions (city-ordinance)
Periodic GMA-mandated comprehensive plan update incorporating ADU framework into Arlington Municipal Code residential chapters.
Effect: Established 900 sqft maximum ADU size, one ADU per residential lot, and dimensional requirements tied to existing residential zone setbacks. - 2023-05-08 — Washington EHB 1337 statewide ADU enabling act (state-law)
Required GMA-planning cities >= 2,500 population to allow two ADUs per single-family lot, drop owner-occupancy, drop parking minimum within 1/2 mile of major transit, and allow up to 1,000 sqft.
Effect: Arlington (population ~21,000, GMA-planning) subject to mandate; preempts Arlington's prior 900 sqft cap and one-ADU-per-lot rule for compliance by June 30, 2025. - 2025-03-18 — Snohomish County Ordinance 25-014 - ADU Reform (county-ordinance)
Snohomish County reformed its ADU code (SCC 30.28) to comply with EHB 1337: 1,200 sqft maximum, 5 ft side/rear setbacks, 30 ft height, allowing condo-conversion of ADUs and removing same-ownership requirement.
Effect: Sets the regional baseline for unincorporated Snohomish County and shapes Arlington's local update. Arlington Council adopted matching code amendments in mid-2025. - 2025-06-30 — Arlington EHB 1337 / HB 1110 compliance amendments (city-ordinance)
AMC residential chapter amendments adopting two ADUs per lot, removing owner-occupancy, raising size cap to 1,000 sqft, and aligning middle-housing types with HB 1110.
Effect: Arlington's local code now conforms to the state floor; Arlington Municipal Airport (KAWO) AICUZ overlay continues to apply additional constraints inside accident potential zones.
Snohomish County — county ADU rules and overlays
County ADU ordinance
Snohomish County, WA (841,000 residents north of Seattle) administers a county code for unincorporated territory under the Washington Growth Management Act (RCW Ch. 36.70A) and the 2023 statewide ADU preemption (HB 1337, codified at RCW 36.70A.681 et seq.). HB 1337 requires Washington counties planning under GMA to permit two ADUs (one attached, one detached, or two attached) on each lot in residential zones, with no owner-occupancy requirement, no minimum lot-size impositions exceeding the underlying district, no off-street parking required for ADUs within 1/2 mile of major transit, and ministerial review for code-compliant applications.
State-floor overlay: Washington HB 1337 preemption is comprehensive; the county ordinance must conform.
County regulatory overlays
Snohomish County administers flood-hazard, and (where mapped) coastal, wildland-fire, historic, and airport overlays that shape ADU project feasibility. The most consistent overlay across the county is FEMA NFIP floodplain regulation; other overlays apply to specific geographies inside the county.
- FEMA NFIP Special Flood Hazard Areas in Snohomish County — A new ADU in a mapped SFHA must be elevated to or above the Base Flood Elevation; cost impact on the project is often material.
- Coastal / hurricane wind exposure — Confirm design wind speed and exposure category at the building department.
- Wildland-Urban Interface (WUI) hazard areas
- Historic districts and individually-listed historic resources
County permitting (unincorporated parcels)
Snohomish County issues building permits for parcels in unincorporated territory through its development services / planning department, with separate review tracks for zoning conformance, building-code compliance, on-site sewage where applicable, floodplain compliance, and addressing. Inside incorporated municipalities, city departments handle their own permits; the county's authority is geographically limited to unincorporated territory. An ADU permit application is typically processed as a residential building permit with a zoning verification step against the county's ordinance for the parcel's zoning district.
Washington state — ADU law and programs
State ADU law
Washington preempts local ADU regulation in urban growth areas of cities and counties subject to the Growth Management Act through Engrossed Second Substitute House Bill 1337 (2023), codified principally at RCW 36.70A.680-.681. Cities and counties planning under the GMA must allow at least two ADUs per lot in urban growth areas, must not require owner-occupancy, must not impose minimum-lot-size or setback rules stricter than those for the primary residence, and must allow ADUs to be sold separately as condominiums. Related House Bill 1110 (2023), codified at RCW 36.70A.635, requires 'middle housing' (duplexes, triplexes, fourplexes) in most residential zones of large cities.
- RCW 36.70A.680 — Accessory dwelling units — Requirements for cities and counties planning under this chapter — Sets the minimum entitlement floor for ADUs in GMA-planning jurisdictions: at least two ADUs per lot in urban growth areas, no owner-occupancy requirement, no stricter setback or lot-coverage rules than for the primary residence, no parking requirements within a half-mile of major transit stops, and no prohibition on selling an ADU separately as a condominium.
- RCW 36.70A.681 — Accessory dwelling units — Design, size, and aesthetic standards — Caps what local governments may require in ADU design and size standards. Maximum ADU size must be at least 1,000 square feet in most zones. Street-facing facades and aesthetic review may not be used to categorically prohibit ADUs.
- RCW 36.70A.696 — Accessory dwelling units — Definitions — Statutory definitions of 'accessory dwelling unit,' 'attached accessory dwelling unit,' 'detached accessory dwelling unit,' 'owner,' and 'urban growth area' used by RCW 36.70A.680-.681.
- RCW 36.70A.635 — Middle housing — Cities planning under this chapter — HB 1110 (2023). Requires cities over specified population thresholds to allow duplexes, triplexes, fourplexes, townhouses, cottage housing, and stacked flats in most residential zones. Interacts with ADU law because ADUs and middle housing both contribute to the state's response to the GMA's housing element.
State HOA preemption
Washington enacted HOA preemption of ADU bans in Substitute House Bill 1337 (2023), which amended the Washington Uniform Common Interest Ownership Act and the Washington Horizontal Property Regimes Act to prohibit common-interest communities from banning ADUs on lots in GMA-planning jurisdictions. A homeowners' association may impose reasonable aesthetic or architectural standards, but may not categorically prohibit ADUs.
- RCW 64.38.057 — Homeowners' associations — Accessory dwelling units — Prohibits a homeowners' association governing a plat within a GMA-planning city or county from recording or enforcing a provision that prohibits the construction, use, or rental of an accessory dwelling unit on a lot. Reasonable design guidelines consistent with RCW 36.70A.681 remain enforceable.
State financing programs
The Washington State Housing Finance Commission (WSHFC) administers state-level housing finance programs. Washington does not currently operate an ADU-specific statewide grant or forgivable-loan program comparable to California's CalHFA ADU Grant, but several state programs can be used for ADU construction when program criteria are met.
State housing programs
Washington supports ADU implementation through Department of Commerce technical assistance and grant programs rather than through a single statewide pre-approved-plan catalog. The state provides model ADU code under the GMA, distributes GMA update grants to help jurisdictions comply with RCW 36.70A.680-.681, and has produced ADU guidance documents for local governments.
Federal (United States) — ADU-relevant rules and programs
Federal ADU law
The United States has no federal statute that directly regulates accessory dwelling unit entitlement or design. Land-use authority over ADUs resides with states and local governments under the traditional police power. Federal engagement is limited to financing (Fannie/Freddie/FHA/VA/USDA), flood insurance (FEMA/NFIP), and discretionary housing programs (HUD), which are recorded in sibling sections of this file.
Federal financing programs
Federal housing-finance agencies and GSEs set nationwide underwriting rules that govern whether an ADU can be financed, appraised, and counted toward mortgage qualifying income. The relevant actors are Fannie Mae, Freddie Mac, FHA (HUD), VA, and USDA Rural Development.
Federal tax credits
There is no ADU-specific federal tax credit. ADUs may incidentally qualify for existing federal energy-efficiency and clean-energy tax credits when the ADU construction includes qualifying measures.
Federal housing programs
HUD administers several discretionary programs that can fund ADU-related activity at the grantee's election, but none is an ADU-specific program.
ZIP Code
- 98223
Post Office
- 3609 168th St NE, 98223
- 524 N Olympic Ave, 98223
Locale Names
- Smokey Point