Growth Management Act.
The Growth Management Act (GMA) is the state's comprehensive land use planning framework for counties and cities.  Eighteen counties and the cities within them are required by population-based criteria to fully plan under the GMA, while other counties and cities can opt to fully plan.  The GMA establishes land use designation and environmental protection requirements for all Washington counties and cities, and a much wider array of planning duties for the fully planning 29 counties.
 
Fully planning jurisdictions are directed to adopt internally consistent comprehensive plans that are generalized, coordinated land use policy statements.  Comprehensive plans must include specific planning elements, each of which is a subset of a comprehensive plan.  Examples include a capital facilities plan, a rural element, and a land use element.  The comprehensive plan must be updated every eight years.  Planning jurisdictions must implement comprehensive plans through locally adopted development regulations that conform to the plan.
 
Urban Growth Areas.
Counties that fully plan under the GMA are required to designate, in consultation with cities, urban growth areas (UGAs) within their boundaries sufficient to accommodate a planned 20-year population projection range.  Each city located within a planning county must be included within a UGA.  Urban growth must be encouraged within the UGAs, and only growth that is not urban in nature can occur outside of UGAs.  Counties and cities must permit urban densities and provide sufficient land capacity suitable for development within UGAs.  Urban governmental services cannot generally be extended to rural areas except in limited circumstances necessary to protect basic public health and safety and the environment.
 
Accessory Dwelling Units.
An accessory dwelling unit (ADU) is a separate living unit located on the same lot as a housing unit that provides complete independent living facilities and includes permanent provisions for living, sleeping, eating, cooking, and sanitation.  A detached accessory dwelling unit is separate and detached from another housing unit.
 
Certain units of local government, including counties planning under the GMA, counties with a population over 125,000, and cities with a population over 20,000, are required to adopt ordinances encouraging the development of ADUs in single-family zones.  The ordinances must incorporate in their development regulations, zoning regulations, or official controls model ordinance recommendations prepared by the Department of Community, Trade, and Economic Development, the predecessor to the Department of Commerce.  The recommendations include standards and criteria regarding size, parking, design, and quantity of ADUs.
 
By July 1, 2021, any city within a county planning under the GMA that has not adopted or substantively amended its ADU regulations within the previous four years must adopt or amend ordinances, regulations, or other official controls that do not require the provision of off-street parking for ADUs within 0.25 mile of a major transit stop, with exceptions.

Detached ADUs that are located outside UGAs will not be included in the calculation of housing density in that area if such ADUs are subject to local development regulations imposing the following limitations:

• no parcel may have more than one ADU;
• the location, size, and appearance of the ADU must be consistent with rural character and may not interfere with any agriculture or other natural resource use of the property;
• detached ADUs must be in close proximity to the primary dwelling unit; and
• the square footage of an ADU may not exceed 50 percent of the square footage of the primary dwelling unit.

 
This change does not apply to detached ADUs in existence as of the effective date of the act.