State Preemption of Local Zoning in Washington
How Washington state law overrides local zoning ordinances. ADU preemption, lot split preemption, and impact on city-level regulations.
What Is State Preemption?
State preemption occurs when a state law overrides local government ordinances in a specific area. In land use, preemption means a city or county cannot adopt zoning rules that are more restrictive than the state standard. If a city tries to prohibit something the state law permits, the state law wins.
Washington actively uses preemption in housing law. The state has enacted legislation that prohibits local governments from blocking certain types of housing development — most notably accessory dwelling units (ADUs) and lot splits.
ADU Preemption
Washington House Bill 1337 (HB 1337) — Expanding Housing Options Through ADUs
This law preempts local ordinances — cities cannot impose rules stricter than the state ADU standard. Effective 2023-07-23.
What local governments cannot restrict:
- Requires all Washington cities and counties planning under the Growth Management Act (GMA) to allow at least 2 ADUs per single-family residential lot by-right
- Prohibits local owner-occupancy requirements for ADUs — neither the primary dwelling nor the ADU must be owner-occupied
- Prohibits local ordinances that cap ADU floor area below 1,000 sqft or 60% of primary dwelling size
- Requires ministerial (administrative) ADU approval — no discretionary design review for ADUs meeting objective standards
- Local jurisdictions had until July 1, 2024 to update their codes to comply
How Preemption Affects Washington Cities
State preemption applies to every incorporated city and unincorporated area in Washington. Select a city below to see how state preemption interacts with local zoning rules.
Source: Washington House Bill 1337 (HB 1337) — Expanding Housing Options Through ADUs. Last verified April 5, 2026. View source