(1) Except as provided in subsection (4) of this section, any city that is required or chooses to plan under RCW 36.70A.040 must provide by ordinance and incorporate into its development regulations, zoning regulations, and other official controls, authorization for the following:

(a) For cities with a population of at least 25,000 but less than 75,000 based on office of financial management population estimates:

(i) The development of at least two units per lot on all lots zoned predominantly for residential use, unless zoning permitting higher densities or intensities applies;

(ii) The development of at least four units per lot on all lots zoned predominantly for residential use, unless zoning permitting higher densities or intensities applies, within one-quarter mile walking distance of a major transit stop; and

(iii) The development of at least four units per lot on all lots zoned predominantly for residential use, unless zoning permitting higher densities or intensities applies, if at least one unit is affordable housing.

(b) For cities with a population of at least 75,000 based on office of financial management population estimates:

(i) The development of at least four units per lot on all lots zoned predominantly for residential use, unless zoning permitting higher densities or intensities applies;

(ii) The development of at least six units per lot on all lots zoned predominantly for residential use, unless zoning permitting higher densities or intensities applies, within one-quarter mile walking distance of a major transit stop; and

(iii) The development of at least six units per lot on all lots zoned predominantly for residential use, unless zoning permitting higher densities or intensities applies, if at least two units are affordable housing.

(c) For cities with a population of less than 25,000, that are within a contiguous urban growth area with the largest city in a county with a population of more than 275,000, based on office of financial management population estimates the development of at least two units per lot on all lots zoned predominantly for residential use, unless zoning permitting higher densities or intensities applies.

(2)(a) To qualify for the additional units allowed under subsection (1) of this section, the applicant must commit to renting or selling the required number of units as affordable housing. The units must be maintained as affordable for a term of at least 50 years, and the property must satisfy that commitment and all required affordability and income eligibility conditions adopted by the local government under this chapter. A city must require the applicant to record a covenant or deed restriction that ensures the continuing rental of units subject to these affordability requirements consistent with the conditions in chapter 84.14 RCW for a period of no less than 50 years. The covenant or deed restriction must also address criteria and policies to maintain public benefit if the property is converted to a use other than which continues to provide for permanently affordable housing.

(b) The units dedicated as affordable must be provided in a range of sizes comparable to other units in the development. To the extent practicable, the number of bedrooms in affordable units must be in the same proportion as the number of bedrooms in units within the entire development. The affordable units must generally be distributed throughout the development and have substantially the same functionality as the other units in the development.

(c) If a city has enacted a program under RCW 36.70A.540, the terms of that program govern to the extent they vary from the requirements of this subsection.

(3) If a city has enacted a program under RCW 36.70A.540, subsection (1) of this section does not preclude the city from requiring any development, including development described in subsection (1) of this section, to provide affordable housing, either on-site or through an in-lieu payment, nor limit the city's ability to expand such a program or modify its requirements.

(4)(a) As an alternative to the density requirements in subsection (1) of this section, a city may implement the density requirements in subsection (1) of this section for at least 75 percent of lots in the city that are primarily dedicated to single-family detached housing units.

(b) The 25 percent of lots for which the requirements of subsection (1) of this section are not implemented must include but are not limited to:

(i) Any areas within the city for which the department has certified an extension of the implementation timelines under RCW 36.70A.637 due to the risk of displacement;

(ii) Any areas within the city for which the department has certified an extension of the implementation timelines under RCW 36.70A.638 due to a lack of infrastructure capacity;

(iii) Any lots designated with critical areas or their buffers that are exempt from the density requirements as provided in subsection (8) of this section;

(iv) Any portion of a city within a one-mile radius of a commercial airport with at least 9,000,000 annual enplanements that is exempt from the parking requirements under subsection (7)(b) of this section; and

(v) Any areas subject to sea level rise, increased flooding, susceptible to wildfires, or geological hazards over the next 100 years.

(c) Unless identified as at higher risk of displacement under RCW 36.70A.070(2)(g), the 25 percent of lots for which the requirements of subsection (1) of this section are not implemented may not include:

(i) Any areas for which the exclusion would further racially disparate impacts or result in zoning with a discriminatory effect;

(ii) Any areas within one-half mile walking distance of a major transit stop; or

(iii) Any areas historically covered by a covenant or deed restriction excluding racial minorities from owning property or living in the area, as known to the city at the time of each comprehensive plan update.

(5) A city must allow at least six of the nine types of middle housing to achieve the unit density required in subsection (1) of this section. A city may allow accessory dwelling units to achieve the unit density required in subsection (1) of this section. Cities are not required to allow accessory dwelling units or middle housing types beyond the density requirements in subsection (1) of this section. A city must also allow zero lot line short subdivision where the number of lots created is equal to the unit density required in subsection (1) of this section.

(6) Any city subject to the requirements of this section:

(a) If applying design review for middle housing, only administrative design review shall be required;

(b) Except as provided in (a) of this subsection, shall not require through development regulations any standards for middle housing that are more restrictive than those required for detached single-family residences, but may apply any objective development regulations that are required for detached single-family residences, including, but not limited to, 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;

(c) Shall apply to middle housing the same development permit and environmental review processes that apply to detached single-family residences, unless otherwise required by state law including, but not limited to, shoreline regulations under chapter 90.58 RCW, building codes under chapter 19.27 RCW, energy codes under chapter 19.27A RCW, or electrical codes under chapter 19.28 RCW;

(d) Shall not require off-street parking as a condition of permitting development of middle housing within one-half mile walking distance of a major transit stop;

(e) Shall not require more than one off-street parking space per unit as a condition of permitting development of middle housing on lots smaller than 6,000 square feet before any zero lot line subdivisions or lot splits;

(f) Shall not require more than two off-street parking spaces per unit as a condition of permitting development of middle housing on lots greater than 6,000 square feet before any zero lot line subdivisions or lot splits; and

(g) Are not required to achieve the per unit density under chapter 332, Laws of 2023 on lots after subdivision below 1,000 square feet unless the city chooses to enact smaller allowable lot sizes.

(7) The provisions of subsection (6)(d) through (f) of this section do not apply:

(a) If a local government submits to the department an empirical study prepared by a credentialed transportation or land use planning expert that clearly demonstrates, and the department finds and certifies, that the application of the parking limitations of subsection (6)(d) through (f) of this section for middle housing will be significantly less safe for vehicle drivers or passengers, pedestrians, or bicyclists than if the jurisdiction's parking requirements were applied to the same location for the same number of detached houses. The department must develop guidance to assist cities on items to include in the study; or

(b) To portions of cities within a one-mile radius of a commercial airport in Washington with at least 9,000,000 annual enplanements.

(8) The provisions of this section do not apply to:

(a) Lots designated with critical areas designated under RCW 36.70A.170 or their buffers as required by RCW 36.70A.170;

(b) A watershed serving a reservoir for potable water if that watershed is or was listed, as of July 23, 2023, as impaired or threatened under section 303(d) of the federal clean water act (33 U.S.C. Sec. 1313(d)); or

(c) Lots that have been designated urban separators by countywide planning policies as of July 23, 2023.

(9) Nothing in this section prohibits a city from permitting detached single-family residences.

(10) Nothing in this section requires a city to issue a building permit if other federal, state, and local requirements for a building permit are not met.

(11) A city must comply with the requirements of this section on the latter of:

(a) Six months after its next periodic comprehensive plan update required under RCW 36.70A.130 if the city meets the population threshold based on the 2020 office of financial management population data; or

(b) 12 months after their next implementation progress report required under RCW 36.70A.130 after a determination by the office of financial management that the city has reached a population threshold established under this section.

(12) A city complying with this section and not granted a timeline extension under RCW 36.70A.638 does not have to update its capital facilities plan element required by RCW 36.70A.070(3) to accommodate the increased housing required by chapter 332, Laws of 2023 until the first periodic comprehensive plan update required for the city under RCW 36.70A.130(5) that occurs on or after June 30, 2034.

Finding—2023 c 332: "The legislature finds that Washington is facing an unprecedented housing crisis for its current population and a lack of housing choices, and is not likely to meet the affordability goals for future populations. In order to meet the goal of 1,000,000 new homes by 2044, and enhanced quality of life and environmental protection, innovative housing policies will need to be adopted.

Increasing housing options that are more affordable to various income levels is critical to achieving the state's housing goals, including those codified by the legislature under chapter 254, Laws of 2021.

There is continued need for the development of housing at all income levels, including middle housing that will provide a wider variety of housing options and configurations to allow Washingtonians to live near where they work.

Homes developed at higher densities are more affordable by design for Washington residents both in their construction and reduced household energy and transportation costs.

While creating more housing options, it is essential for cities to identify areas at higher risk of displacement and establish antidisplacement policies as required in Engrossed Second Substitute House Bill No. 1220 (chapter 254, Laws of 2021).

The state has made historic investments in subsidized affordable housing through the housing trust fund, yet even with these historic investments, the magnitude of the housing shortage requires both public and private investment.

In addition to addressing the housing shortage, allowing more housing options in areas already served by urban infrastructure will reduce the pressure to develop natural and working lands, support key strategies for climate change, food security, and Puget Sound recovery, and save taxpayers and ratepayers money." [ 2023 c 332 § 1.]