ADU Rules in Marysville, Washington

Marysville (population ~70,000) is one of the fastest-growing cities in Snohomish County, located north of Everett along the I-5 corridor on the edge of the Puget Sound lowlands. The city has grown dramatically as a bedroom community for the greater Seattle-Everett metro area, with rapid residential development over the past two decades. Marysville is adjacent to the Tulalip Tribes reservation to the west — home to one of Washington's most successful tribal nations, known for the Tulalip Resort Casino and extensive natural resource management. Ebey Slough and the Snohomish River delta form part of Marysville's western boundary. The city is subject to Washington's statewide ADU reform laws.

Washington State ADU Law: HB 1337 (2023)

Washington HB 1337 (2023) is the foundational statewide ADU law that applies to Marysville. Key requirements:

• Cities must allow up to 2 ADUs per lot — one attached/internal + one detached — by right on any lot with a single-family home
• No owner-occupancy requirement permitted
• No ADU-specific impact fees allowed
• Cities may not require ADUs smaller than 1,000 square feet
• State law limits how restrictive local setback, lot coverage, and height standards for ADUs can be

Washington HB 1110 (2023) accompanies HB 1337, requiring Marysville to allow duplexes and middle housing in residential zones.

Marysville is subject to the Washington Growth Management Act (GMA) and has a comprehensive plan with an Urban Growth Area coordinated with Snohomish County. Given Marysville's rapid growth, GMA planning for adequate housing and infrastructure is particularly important.

Marysville Local ADU Code

Marysville's Community Development Department administers local zoning and building permits. Local ADU regulations must comply with HB 1337.

Permitted ADU Types

• Detached ADU: A standalone structure in the rear or side yard
• Attached ADU: An addition to the primary home sharing at least one wall
• Internal/Converted ADU: Conversion of existing garage, basement, or other space

Up to 2 ADUs per lot are permitted (one attached/internal + one detached).

Size Limits

State law prohibits Marysville from requiring ADUs smaller than 1,000 square feet. Confirm current maximum size limits for your zone with Marysville's Community Development Department.

Setbacks

HB 1337 limits Marysville's ability to impose setbacks that would prevent reasonable ADU construction. Setback requirements vary by zoning district. Verify current standards with the city before designing.

No Owner-Occupancy Requirement

State law prohibits owner-occupancy mandates. Marysville cannot require property owners to live on-site to rent an ADU.

Tulalip Tribes — Tribal Land Distinction

Marysville is directly adjacent to the Tulalip Indian Reservation — the home of the Tulalip Tribes (comprising Snohomish, Snoqualmie, Skykomish, and allied tribes). The Tulalip Tribal government has sovereign jurisdiction over tribal trust lands. Marysville city zoning applies only to properties within Marysville's incorporated city limits. If your property is on the Tulalip Reservation, contact the Tulalip Tribes Planning Department for applicable land use regulations, as they differ from state and city standards.

Critical Areas Ordinance (CAO)

Marysville's CAO protects Ebey Slough (a tidal slough and salmon habitat corridor), the Snohomish River delta wetlands, freshwater wetlands, frequently flooded areas (significant given the low-lying river delta terrain), steep slopes, and critical aquifer recharge areas. Many parts of Marysville's western and northern areas have extensive wetland systems. FEMA-mapped floodplains are widespread in the delta areas. CAO buffers can significantly restrict ADU siting on wetland-adjacent properties. Review Marysville's GIS mapping carefully before designing an ADU.

Seismic Hazard

Marysville and Snohomish County face seismic risk from the Cascadia Subduction Zone (CSZ). Low-lying delta areas near Ebey Slough and the Snohomish River have soft marine and alluvial sediments susceptible to liquefaction. All ADU construction must meet Washington State Building Code seismic requirements. Geotechnical review is recommended for properties on soft or fill soils.

Permit Process

1. Check your property's zoning, flood zone, and CAO constraints using Marysville's GIS portal
2. Contact Marysville's Community Development Department for pre-application guidance
3. Prepare construction plans meeting Washington State Building Code requirements
4. Submit permit application at marysvillewa.gov or in person at 80 Columbia Avenue
5. Plan review and permit issuance
6. Construction inspections
7. Final inspection and Certificate of Occupancy

Contact Marysville Community Development: (360) 363-8100 | marysvillewa.gov

Disclaimer: This guide provides general information based on Washington HB 1337 (2023) and Marysville's municipal code as of April 2026. Zoning regulations change frequently. Properties on the Tulalip Indian Reservation are not subject to city zoning — contact the Tulalip Tribes Planning Department for tribal land use information. Always verify current requirements with Marysville Community Development before making development decisions. This is not legal advice.