This bill adds a new section to chapter 36.70A RCW to allow counties that are required or choose to plan under RCW 36.70A.040 to authorize “middle housing” by ordinance and incorporate that authorization into development regulations, zoning, and other official controls. The text requires authorization of at least one middle housing unit on each parcel that permits single-family residences in designated urban growth areas and in applicable limited areas of more intensive rural development, and it caps middle housing at no more than four residential units per lot in those limited rural areas where the county takes the authorized action. County development regulations for middle housing in those limited rural areas must not be more restrictive than standards for detached single-family residences (while allowing objective rules that apply to detached single-family homes), must use the same development permit and environmental review processes as detached single-family residences except where state law requires otherwise, and must require sewer service for middle housing in those limited rural areas. The bill does not define “middle housing” in the provided text. The bill reenacts and amends RCW 43.21C.495 to make specified city and county nonproject actions and the adoption or amendment of development regulations (including certain actions from prior 2022 law and several cited RCW provisions) not subject to administrative or judicial appeals under chapter 43.21C RCW, with a narrow exception if the adoption has a probable significant adverse impact on fish habitat. It also reenacts and amends RCW 36.70A.280 to more narrowly define the categories of petitions the Growth Management Hearings Board (GMHB) may hear, to define who may file petitions and who counts as a “person,” to set standing rules for petitioners based on prior participation (participation must be reasonably related to the issue), and to set procedures and limits if the GMHB adopts an adjustment to an OFM 20-year growth-management population projection. If the board adjusts a county projection it must document its rationale and file it with OFM within ten working days, and any board-adjusted projection may be used only for planning under the chapter and does not change OFM’s official state or county forecasts. Overall, the bill creates a new statutory section enabling and regulating middle housing at the county level, and makes procedural and administrative changes to appeal rights, petition standing, and the handling of OFM population projections by reenacting and amending existing RCW sections. The text provided does not include a definition of “middle housing,” does not show any changes to criminal penalties, and omits specifics referenced by cross-references (for example, the precise actions in “section 2, chapter 246, Laws of 2022” and which “department” is referenced in some approvals), so those details cannot be determined from the provided material.

If enacted, counties that plan under state law would be able to require or allow at least one additional middle housing unit on any parcel that currently permits a single-family home in urban growth areas and in certain designated rural areas, with a four-unit cap in those limited rural areas. That will push counties to rewrite zoning and development regulations to treat these units no more restrictively than detached single-family homes, use the same permit and environmental review processes, and, in the rural limited areas, require sewer service — meaning counties face administrative work to update rules, property owners and builders gain more opportunities to add units but may face sewer hookup costs or limits, and sewer providers or local utilities could see increased demand or need for extensions. The bill also narrows who can appeal related local nonproject land use decisions and shields many county and city ordinance changes implementing the law from appeals under the state environmental review statute, except where a change probably significantly harms fish habitat, and it tightens standing rules for the growth management hearings board while requiring documented rationale if the board alters OFM population projections (and limits those adjusted projections to planning use). In practice this reduces the likelihood and cost of litigation for counties and cities and gives developers greater certainty, while limiting options for members of the public to challenge such local actions; however, key details are missing from the provided text — notably a definition of "middle housing," which specific 2022 actions are being referenced, and which agency reviews greenhouse gas subelements — so some implementation effects remain uncertain.