The process by which land divisions may occur is governed by state and local requirements. Local governments must adopt associated ordinances and procedures in conformity with state requirements.

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Subdivisions. Subdivisions are the divisions or redivisions of land into five or more lots, tracts, parcels, sites, or divisions for the purpose of sale, lease, or transfer of ownership.

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Short subdivisions are the division or redivision of land into four or fewer lots, tracts, parcels, sites, or divisions for the purpose of sale, lease, or transfer of ownership. Any city or town may increase the number of lots that can be regulated as short subdivisions up to a maximum of nine. Counties planning under the Growth Management Act (GMA) may do the same with respect to unincorporated land within an urban growth area.

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Unit lot subdivision refers to the division of a parent lot into separately owned unit lots. Local governments must include in their short plat regulations procedures for unit lot subdivisions allowing division of a parent lot into separately owned unit lots. Portions of the parent lot not subdivided for individual unit lots must be owned in common by the owners of the individual unit lots, or by a homeowners' association comprised of the owners of the individual unit lots.

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Growth Management Act. The 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.

All cities, code cities, and towns fully planning under the GMA must adopt or enact procedures for unit lot subdivisions by June 30, 2026. These procedures must include, at a minimum, the requirement that prominent informational notes be placed on the unit lot subdivision's plat, and recorded in the county or counties in which the land is located, to acknowledge each of the following:

• approval of the design and layout of the unit lot's housing development project was granted based on detailed review of that specified project on the parent lot;
• subsequent subdivision actions to the unit lot housing development project's structures may not create or increase any nonconformity of the parent lot and must conform to the approved unit lot housing development project or to the land use and development standards in effect at the time of the proposed actions;
• if a structure or portion of a structure within the unit lot housing development project has been damaged or destroyed, any repair or replacement must conform to the approved unit lot housing development project or to the land use and development standards in effect at the time the proposed repair or replacement project's permit application becomes vested; and
• additional development or redevelopment of the individual unit lots may be limited based on the application of the development standards to the parent lot.

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These procedures must also:

• not require a public predecision meeting or hearing, or any design review other than administrative design review;
• apply only clear and objective development regulations;
• be integrated with the application, review, and approval procedures that apply to the underlying unit lot housing development project to the greatest extent feasible; and
• be specifically subject to the maximum permit processing time period for local government actions, unless extended pursuant to project-specific mutual agreement.

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After June 30, 2026, a city, code city, or town that has not adopted or enacted procedures may not decline to process an application for a unit lot subdivision, consistent with the procedural requirements, solely because that city, code city, or town has not adopted or enacted the procedures.

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A city or county is not prohibited from applying public health, safety, building code, and environmental permitting requirements to a development project that is subject to or integrated with a unit lot subdivision process.

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A city or county is not required to authorize a development project or a unit lot subdivision in a location where development is restricted under other laws, rules, or ordinances, such as in locations where development is limited as a result of physical proximity to on-site sewage system infrastructure, critical areas, or other unsuitable physical characteristics of a property.