SENATE BILL REPORT
SB 5470
As of January 30, 2025
Title: An act relating to establishing limitations on detached accessory dwelling units outside urban growth areas.
Brief Description: Establishing limitations on detached accessory dwelling units outside urban growth areas.
Sponsors: Senators Goehner, Bateman, Chapman, Frame, Gildon, Nobles and Salda?a.
Brief History:
Committee Activity: Housing: 1/31/25.
Brief Summary of Bill
  • Allows counties to authorize detached accessory dwelling units (ADUs) outside of urban growth areas (UGAs) if the detached ADUs are subject to development regulations that include certain limitations, including that a parcel have no more than one attached or detached ADU.
  • Requires that counties allowing ADUs outside of UGAs follow certain reporting and land use plan update requirements.
SENATE COMMITTEE ON HOUSING
Staff: Benjamin Omdal (786-7442)
Background:

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 obligated to satisfy all planning requirements of the GMA.

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The GMA directs fully planning jurisdictions to adopt internally consistent comprehensive land use plans.? Comprehensive plans are implemented through locally adopted development regulations, and both the plans and the local regulations are subject to review and revision requirements prescribed in the GMA.? Comprehensive plans must contain certain elements, such as a land use element, a rural element, and a housing element.

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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.

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Urban Growth Areas.? Counties that fully plan under the GMA are required to designate urban growth areas (UGAs) within their boundaries sufficient to accommodate a planned 20-year population projection range provided by the Office of Financial Management.? 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 the UGAs.

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Accessory Dwelling Units.? Under the GMA, an ADU is defined as a dwelling unit that is 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.

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An attached accessory dwelling unit is defined as an ADU located within or attached to the principal unit, and a detached accessory dwelling unit 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.

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Requirements for Development of Accessory Dwelling Units Within Urban Growth Areas.? Beginning six months after its next periodic comprehensive plan update, a fully planning city or county must ensure local development regulations allow for the construction of ADUs 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 2000 square feet or less.

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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.

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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.

Summary of Bill:

Counties may allow detached ADUs outside of UGAs if the detached ADUs are subject to development regulations that include certain limitations.? These include:

  • no parcel may have more than one attached or detached ADU;
  • the detached ADU is subject to statutory water supply requirements and any groundwater mitigation requirements adopted by the county or Department of Ecology;
  • the applicant must provide documentation that the existing or proposed sewage or septic system is capable of handling the additional demand from the detached ADU;
  • the gross floor area of the detached ADU may not exceed the gross floor area of what could be authorized as an attached ADU and, in no case, exceed 1296 square feet;
  • the detached ADU must be sited within 150 feet of the principal unit;
  • a parcel may not be subdivided for the purposes of avoiding the limits on regulations in this act;
  • certain limitations on usage as a principal unit;
  • if the ADU is offered as a short-term rental, the primary unit must be owner-occupied; and
  • the combined water withdrawal may not exceed statutory limitations for domestic use.

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Counties may allow detached ADUs outside of UGAs if the county tracks and reports annually the number of detached ADUs to the Department of Commerce, updates the county's comprehensive land use plan during required reviews to properly account for the number of detached ADUs, and abides by amendment frequency requirements.

Appropriation: None.
Fiscal Note: Requested on January 29, 2025.
Creates Committee/Commission/Task Force that includes Legislative members: No.
Effective Date: Ninety days after adjournment of session in which bill is passed.