Growth Management Act.

The Growth Management Act (GMA) is the comprehensive land-use planning framework for counties and cities in Washington.  The GMA establishes land-use designation and environmental protection requirements for all Washington counties and cities.  The GMA also establishes a significantly wider array of planning duties for 28 counties, and the cities within those counties, that are required or have chosen to plan under the GMA.  These jurisdictions are sometimes said to be "fully planning" under the GMA. 

Fully planning cities and counties must adopt internally consistent comprehensive land-use plans that are generalized, coordinated land-use policy statements of the governing body.  When developing comprehensive plans, cities and counties must consider specific planning goals related to certain subjects, such as urban growth, reduction of sprawl, transportation, and housing.  Each comprehensive plan must include certain mandatory elements, including land use, housing, capital facilities, utilities, rural areas, transportation, economic development, parks and recreation, and climate change and resiliency.  The housing element must ensure the vitality and character of established residential neighborhoods and, among other requirements, consider the role of accessory dwelling units (ADUs) in meeting housing needs. 

Fully planning counties must designate urban growth areas (UGAs), within which urban growth must be encouraged and outside of which growth may occur only if it is not urban in nature.  Each city in a fully planning county must be included in a UGA, and UGAs must include sufficient areas and densities to accommodate projected urban growth for the succeeding 20-year period. 

A comprehensive plan and any locally adopted development regulations must be reviewed and, if necessary, revised every 10 years to ensure compliance with the GMA.  Certain cities and counties are also required to provide implementation progress reports detailing the progress they have achieved in implementing their comprehensive plans five years after the required 10-year review and revision.  Comprehensive plan update deadlines for each county, and the cities within those counties, are specified in the GMA.  Amendments to a comprehensive plan may occur no more frequently than once per year, with certain exceptions. 

Accessory Dwelling Units.

Under the GMA, an ADU is defined as a dwelling unit located on the same lot as a single-family housing unit, duplex, triplex, townhome, or other housing unit, which is referred to as the principal unit.  A dwelling unit means a residential living unit that provides complete independent living facilities for one or more persons and permanent provisions for living, sleeping, eating, cooking, and sanitation.

An attached accessory dwelling unit (AADU) is defined as an ADU located within or attached to the principal unit, and a detached accessory dwelling unit (DADU) is defined as an ADU that consists partly or entirely of a building that is separate and detached from the principal unit and is on the same property. 

Requirements for Development of Accessory Dwelling Units within Urban Growth Areas.

As of July 23, 2023, beginning six months after its next periodic comprehensive plan update, a fully planning city or county must ensure local development regulations allow ADU construction within UGAs and comply with certain policies related to siting and permitting of ADUs.  A city or county may impose a limit of two ADUs, in addition to the principal unit, on a residential lot of 2,000 square feet or less.

A city or county may not authorize the construction of an ADU in a location where development is restricted under other laws, rules, or ordinances as a result of physical proximity to on-site sewage system infrastructure, critical areas, or other unsuitable physical characteristics of a property.  Certain provisions related to off-street parking for ADUs are also specified.

None of these ADU requirements apply to lots designated with critical areas, critical area buffers, or a watershed serving as a reservoir for potable water if that watershed is or was listed as impaired or threatened under the United States Clean Water Act.  Cities and counties are not prohibited from enforcing certain development regulations on ADUs.

Requirements for Development of Detached Accessory Dwelling Units Outside of Urban Growth Areas.

Fully planning counties may allow DADUs outside of UGAs if the DADUs are subject to certain development regulations, the county has certain code enforcement measures in place, and the county takes certain actions to account for DADU development.  

Development Regulations.

Any DADUs allowed outside of UGAs must be subject to development regulations that include the following limitations:

• no parcel may have more than one ADU, whether attached or detached;
• the DADU must be subject to certain water supply requirements specified in the State Building Code and any groundwater mitigation requirements adopted by the county or the Department of Ecology;
• the combined water withdrawal for the DADU, the principal unit, and any other domestic uses on the parcel may not exceed certain use limitations for domestic use specified in the state laws regulating public groundwaters;
• withdrawals of water by each dwelling unit on the parcel must be metered;
• the applicant must provide documentation that the sewage or septic system can handle the additional demand from the DADU;
• the gross floor area of the DADU may not be greater than 1,296 square feet and may not exceed the area that could be authorized by the county as an expansion of the principal unit to create an AADU.  Floor areas exclude garages, porches, and unfinished basements;
• the DADU must use the same driveway or other means of ingress and egress as the principal unit;
• the DADU must be sited within 150 feet of the principal unit;
• the DADU may be the existing principal unit if the existing principal unit meets these requirements, is a single-family dwelling, and a new principal unit that is a single-family dwelling unit is constructed on the same parcel;
• the DADU must not be allowed on nonconforming lots under one acre; and
• a parcel may not be subdivided for the purposes of avoiding these requirements.

Code Enforcement Measures.

Counties that allow DADUs outside of UGAs must have certain code enforcement measures in place, including a voluntary code compliance process for the owner of an unpermitted DADU to bring the DADU into compliance with applicable regulations.  When the owner of an unpermitted DADU seeks to bring the DADU into compliance, a permit penalty of at least double the normal permit fee must be applied.

Owners who do not seek voluntary compliance and are found to have a DADU without the required permits must be subject to a civil infraction of at least $1,000 and must be required to remove the DADU or ensure that it meets all existing development regulations.  A penalty of at least triple the normal permit fee must be applied if the DADU remains.

Any owner who does not seek voluntary compliance and has received a civil infraction for having an unpermitted ADU must be prohibited from receiving any permits for construction or placement of new ADUs for a period of at least three years.

Accounting for Detached Accessory Dwelling Unit Development.

Any county that allows DADUs outside of UGAs must also take certain actions to account for DADU development, including tracking and annually reporting the number of completed DADU permits to the Department of Commerce (Commerce).  During its next required comprehensive plan review and all subsequent reviews, a county must use this data to update its comprehensive plan to properly account for the actual and projected development of DADUs so that the housing units will not exceed the underlying densities for the comprehensive plan designations and zones outside of UGAs.  The county must limit the frequency of these future comprehensive plan amendments to occur no more than once every five years.

Limits on Population Growth Targets.

Counties that allow DADUs outside of UGAs must include the following limits on population growth targets in their comprehensive plans:

• rural counties may allocate no more than 10 percent of their rural population target to DADUs; and
• counties that are not rural may allocate no more than 7 percent of their rural population target to DADUs.

A "rural county" is defined by cross-reference as a county with a population density of fewer than 100 persons per square mile or a county smaller than 225 square miles, as determined by the Office of Financial Management and published each year by Commerce for the period from July 1 to June 30.

Other Provisions.

The act does not affect or modify the validity of any county ordinance authorizing ADUs adopted before the effective date of the act; exclude other means of authorizing ADUs in urban or rural areas, if consistent with the act; or exclude certain other innovative techniques allowed under the GMA, if consistent with the act.