WSDC: Guidance for Accessory Dwelling Units in Washington State

From the Washington State Department of Commerce: Guidance for Accessory Dwelling Units in Washington State: Allowing more accessory dwelling units (ADUs) encourages housing construction and increases the overall supply and variety of housing options, helping address the challenges posed statewide by insufficient housing.

HB 1337, passed in 2023, requires jurisdictions to allow two ADUs per lot within urban growth areas (UGAs)by six months after the next periodic update due date. The Washington State Department of Commerce (Commerce) presents this publication as an update to the agency's 1994 guidance to assist local governments in implementing this requirement. The objective is to provide information on the requirements, local policy choices, and examples of approaches for consideration by cities, towns, and counties, in accordance with the bill. This guidance is structured into the following sections:

• Requirements for cities and other urban areas.

• Recommendations for cities and other urban areas.

• Key considerations for counties (rural and resource lands).

• Other programmatic elements to consider.

Benefits of ADUs

Construction of new ADUs has many benefits, including to:

• Add to the diversity of housing options.

• Provide a housing type that blends in well with existing low density residential neighborhoods.

• Cater to our state’s changing demographics, including more seniors and smaller household sizes.

• Provide housing that is typically more affordable than traditional detached single-family homes.

• Add housing units without expanding urban growth areas.

• Correct historic economic and racial exclusion by opening up single-family neighborhoods to more diverse housing and household types.

• Reduce climate impacts because ADUs tend to be smaller and use less energy than traditional single-family homes.

• Use existing infrastructure such as sewer, water and streets.

For these reasons, ADUs can be an effective and “gentle” way of helping to accommodate the state’s growing population.