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.  These jurisdictions are sometimes said to be fully planning under the GMA.

Counties that fully plan under the GMA 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 county must be included in a UGA.  Planning jurisdictions must include within their UGAs sufficient areas and densities to accommodate projected urban growth for the succeeding 20-year period.

The GMA also 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.  When developing their comprehensive plans, counties and cities must consider various goals set forth in statute.  Fully planning counties and cities must review and, if necessary, revise their comprehensive plans every 10 years to ensure they comply with the GMA.  
 
Each comprehensive plan must include a plan, scheme, or design for certain mandatory elements, including a housing element.  The housing element must ensure the vitality and character of established residential neighborhoods.

Middle Housing.
No later than six months after its next required comprehensive plan update, fully planning cities meeting population requirements must allow for the development of a minimum number of units on all residential lots as follows:

• Cities with a population of at least 75,000 must allow at least four units on all residential lots, at least six units on all residential lots within 0.25 miles walking distance of a major transit stop, and at least six units if two are affordable housing.
• Cities with a population of at least 25,000 but less than 75,000 must allow at least two units on all residential lots, at least four units on all residential lots within 0.25 miles walking distance of a major transit stop, and at least four units if one unit is affordable housing.
• Cities with a population less than 25,000, within a contiguous UGA with the largest city in a county with a population of more than 275,000, must allow two units on all residential lots. 

A major transit stop is defined as a stop on a high-capacity transportation system, commuter rail stops, stops on rail or fixed guideway systems, and stops on bus rapid transit routes.

The density requirements do not apply to:

• lots designated with critical areas or their buffers;
• a watershed serving a reservoir for potable water if that watershed is listed as impaired or threatened under the federal Clean Water Act; or
• lots that have been designated urban separators by countywide planning policies.

A city must allow at least six of the nine types of middle housing and may allow accessory dwelling units (ADUs) to achieve the minimum density requirements.  Middle housing is defined as buildings that are compatible in scale, form, and character with single-family houses and contain two or more attached, stacked, or clustered homes including duplexes, triplexes, fourplexes, fiveplexes, sixplexes, townhouses, stacked flats, courtyard apartments, and cottage housing.  The GMA defines courtyard apartments as up to four attached dwelling units on two or three sides of a court. 

A city subject to the minimum density requirements must include specific provisions for middle housing in its development regulations and may not require any standards for middle housing that are more restrictive than those required for detached single-family residences.  A city may apply any objective development regulations to middle housing that are required for detached single-family residences, including set-back, lot coverage, stormwater, clearing, and tree canopy and retention requirements to ensure compliance with existing ordinances intended to protect critical areas and public health and safety.

As an alternative, a city subject to the minimum density requirements may choose to implement the requirements for at least 75 percent of lots in the city that are primarily dedicated to single-family detached housing units.  In addition, a city may apply to the Department of Commerce (Commerce) for extensions from the implementation timelines for areas at risk of displacement or where a city can demonstrate that infrastructure or fire protection services lack capacity to accommodate an increased density.

Fully planning cities are limited in their ability to establish minimum off-street parking requirements for middle housing and may not require:  (1) off-street parking within 0.5 miles walking distance of a major transit stop; (2) more than one off-street parking space per unit for lots smaller than 6,000 square feet; and (3) more than two off-street parking spaces per unit for lots greater than 6,000 square feet.  The limits do not apply if a city submits an empirical study that clearly demonstrates, and Commerce certifies, that parking limitations for middle housing are significantly less safe than if the jurisdiction's parking requirements were applied to the same location for the same number of detached houses.   

Minimum Residential Parking Requirements. 
In addition to requirements for middle housing, the GMA contains limits on the ability of fully planning cities and counties to establish minimum off-street parking requirements for other types of housing, including:

• For affordable housing for very low-income and extremely low-income individuals located within 0.25 miles of a transit stop that receives transit service at least two times per hour for at least 12 hours per day, no more than one parking space per bedroom or 0.75 of a parking space per unit may be required. 
• For housing units designed for seniors and people with disabilities located within 0.25 miles of a transit stop that receives transit service at least four times per hour for at least 12 hours per day, no minimum residential parking limitations may be imposed.
• For market rate multifamily housing units located within 0.25 miles of a transit stop that receives transit service from at least one route that provides service at least four times per hour for at least 12 hours per day, no more than one parking space per bedroom or 0.75 of a parking space per unit may be required.
• For ADUs located within 0.5 miles walking distance of a major transit stop, no minimum residential parking requirements may be imposed.
• For ADUs located within 0.25 miles of a stop on a route that runs on high occupancy vehicle (HOV) lanes or receives transit service at least four times per hour for at least 12 hours per day, no minimum residential parking requirements may be imposed.
• For all other ADUs, no more than one or two off-street parking spaces may be required, depending on the size of the lot.  

In some cases, cities and counties may vary from these requirements if the jurisdiction has determined that a particular housing unit or lot is an area with a lack of access to street parking capacity, physical space impediments, or other reasons supported by evidence that would make on-street parking infeasible.  In other cases, a city or county may vary from the requirements only after an empirical study prepared by a credentialed transportation or land use planning expert determines parking limits would create a significant safety issue.

Middle Housing.
A city with at least 25,000 population that is subject to minimum residential density requirements must allow at least six of the nine types of middle housing.  A city with less than 25,000 population may choose the number of types of middle housing to allow to meet minimum residential density requirements.  The four-unit limit in the definition of courtyard apartments is removed. 

The minimum density requirements for residential lots within 0.25 miles walking distance of a major transit stop must be applied to any future stop on a bus rapid transit route funded for development and projected for construction within an applicable six-year transit plan. 

In applying objective development regulations to middle housing, fully planning cities may apply regulations related to set-back, lot coverage, stormwater, clearing, and tree canopy and retention requirements, and language related to compliance with existing ordinances intended to protect critical areas and public health and safety is removed.

The exemption from minimum density requirements for lots with critical areas or their buffers is limited to that portion of a lot with a critical area or buffer except for critical aquifer recharge areas where a single-family detached house is an allowed use provided that any requirements to maintain aquifer recharge are met.  Until June 30, 2026, any additional residential capacity required by lots with critical areas or critical area buffers may not be considered an inconsistency with countywide planning policies, multicounty planning policies, or growth targets. 

Lots created through the splitting of a single residential lot are exempt from the minimum density requirements.  

A city subject to the minimum density requirements may not require more than one off-street parking space per unit for middle housing constructed on lots that are exactly 6,000 square feet before any zero lot line subdivisions or lot splits.

Minimum Residential Parking Requirements.
The limits on establishing minimum off-street parking requirements for market rate multifamily housing and housing for very low-income and extremely low-income individuals, seniors, and people with disabilities apply within 0.25 miles of a major transit stop, which is defined as a stop on a high-capacity transportation system, commuter rail stops, stops on rail or fixed guideway systems, and stops on bus rapid transit routes.  Limits on off-street parking near transit stops that receive transit service at least two or four times per hour for at least 12 hours per day are removed. 

The limits on establishing minimum off-street parking requirements for ADUs located within 0.25 miles of a stop on a route that runs on HOV lanes or receives transit service at least four times per hour for at least 12 hours per day is removed.