(1) Cities shall include in their development regulations a process through which an applicant can seek review and approval of an administrative lot split, which may be combined with concurrent review of a residential building permit to create new middle housing, as defined in RCW 36.70A.030 , or single-family housing. The application process for a residential lot to be split may require only an administrative decision, through which the application is reviewed, approved, or denied by the planning director or other designee based on applicable clear and objective development standards, with neither a predecision public hearing, nor any design review other than administrative design review. A new buildable residential lot and residential building permit or permits must be administratively approved and are not subject to administrative appeal if they comply with applicable development standards and the following conditions are met:
(a) No more than one newly created lot is created through the administrative lot split;
(b) Both the parent lot and the newly created lot meet the minimum lot size allowed under applicable development regulations;
(c) The parent lot was not created through the splitting of a residential lot authorized by this section;
(d) The parent lot is located in a residential zone and not in an exclusively nonresidential zone including, but not limited to, zones that are exclusively commercial, retail, agricultural, or industrial;
(e) If the lot split would require demolition or alteration of any existing housing that would displace a renter, the applicant must recommend a displacement mitigation strategy that may include, but is not limited to, relocation assistance;
(f) The applicable sewer and water purveyors have issued certificates of availability to serve the newly created lot and dwelling units;
(g) Access and utility rights are granted or conveyed as necessary on or before recording of the lot split survey to provide access for the maximum number of dwelling units that could be developed on the newly created lot, provided such access rights may be reduced consistent with a city's adopted codes, regulations, or design standards as applicable through review of a subsequent application for a building permit, short subdivision, unit lot subdivision, subdivision application, or short subdivision if less than the maximum number of dwelling units are built on the newly created lot;
(h) The planning director or other designee determines that the application follows all applicable development regulations; and
(i) The lot split survey has been approved by the planning director or other designee and includes a condition on the face of the survey that further lot splits of the parent lot and newly created lot are not authorized by this section.
(2) A proposed lot split may be conditioned upon dedication of right-of-way on the parent lot to the extent such dedication is required under applicable codes, regulations, and design standards for the development, short plat, or subdivision of the parent lot absent an administrative lot split.
(3) Development of dwelling units on the newly created lot may be conditioned upon construction of frontage improvements to a right-of-way adjacent to either the parent lot or the newly created lot to the extent required under applicable codes, regulations, and design standards.
(4) Any construction on the newly created lot is subject to all existing state and local laws including those specified in this section. Nothing in this section modifies the requirements for approval of residential building permits in chapter 19.27 RCW.
(5) A city subject to the requirements of this section may not impose a limit on the total number of dwelling units allowed on the parent lot or newly created lot that is less than the number of dwelling units allowed by the underlying zoning of the parent lot prior to the administrative lot split.
(6) Notwithstanding the provisions of this section, lots that are not buildable according to locally adopted development regulations including, but not limited to, critical areas, shorelines, stormwater, setbacks, impervious surface areas, and building coverage standards, are not eligible for a lot split under this section.
(7) If a lot split results in a lot of a size that would allow for further land division, the lot is not eligible for a lot split but may be divided under other applicable land subdivision processes.
(8) The newly created lot must meet any locally adopted minimum density requirements.
(9) Cities are immune from any liability, loss, or other damage suffered by another that is related to the city's approval of a lot split under chapter 301, Laws of 2025, including if the lot split creates a lot that is later determined to not be buildable.
(10) Parent lots and newly created lots approved under this section must have a lot split survey recorded with the county auditor with a notation that future lot splits are not allowed on the lot.
(11) An application process or a residential lot to be split under this section is subject to the maximum time period for local government actions as set forth in RCW 36.70B.080 , unless extended pursuant to project-specific mutual agreement as permitted by RCW 36.70B.080 .
(12) Ordinances adopted to comply with this section are not subject to administrative or judicial appeal under chapter 43.21C RCW.
(13) The department of commerce must develop guidance for cities in implementing the lot splitting requirements.
(14) A city required to comply with the requirements of this section that has its next comprehensive plan update due in 2027, pursuant to RCW 36.70A.130 , must adopt or amend by ordinance, and incorporate into its development regulations, zoning regulations, and other official controls, the requirements of this section in its next comprehensive plan update. All other cities required to comply with this section must implement the requirements within two years of July 27, 2025.
(15) For the purposes of this section, the following definitions apply unless the context clearly requires otherwise:
(a) "Lot split" means the administrative process of dividing an existing lot into two lots for the purpose of sale, lease, or transfer of ownership pursuant to this section.
(b) "Lot split survey" means the final survey prepared for filing for record with the county auditor and containing all elements and requirements for a lot split under this section and any local regulations.
(c) "Newly created lot" means a lot that was created by a lot split under this section.
(d) "Parent lot" means a lot that is subjected to a lot split under this section.
(16) The provisions of this section do not apply to areas designated as sole-source aquifers by the United States environmental protection agency on islands in the Puget Sound.
Findings — Intent — 2025 c 301: "The legislature finds that allowing an existing residential lot to be split to create a new residential lot through a simple, administrative process can offer many advantages to both the existing homeowner and to prospective homebuyers. The legislature further finds that administrative lot splitting can provide current owners the opportunity to maintain homeownership in changing life circumstances while facilitating development of middle housing to provide homebuyers, including first-time homebuyers, with more affordable ownership opportunities. The legislature also finds that lot splitting can be combined with the review of a residential building permit application to create a single integrated process benefiting both homeowners and cities. Therefore, it is the intent of the legislature to ease restrictions on, and expand opportunities for, lot splitting in cities." [ 2025 c 301 s 1 .]