SB 5559 would standardize unit lot subdivision procedures to speed middle-housing within urban growth areas

Senate Bill 5559 would require cities, towns and code cities planning under the Growth Management Act to adopt procedures for unit lot subdivisions (ULSs) by June 30, 2026, and sets minimum statutory requirements for those procedures. The bill aims to integrate unit-lot processes into existing subdivision statutes so developers, lenders and buyers have clearer rules when townhouses or other attached housing are divided into separately owned parcels.

Committee staff described ULSs as a way to divide a parent parcel into separately owned unit lots where the individual unit lots may be smaller than underlying zone minimums but were approved as part of a specific housing development project; the statute would require prominent notes on recorded plats and would limit additional subdivision actions that would increase nonconformity. The bill also requires only clear-and-objective development regulations and administrative design review for the unit-lot process and says jurisdictions may still apply public-health, building-code and environmental regulations.

Sponsor Sen. Liz Leavitt said the proposal grew from stakeholder work to ensure infill is buildable and to give consumers and local governments more certainty that a parent lot was approved for a specific unit-lot housing project. “This is kind of my stab at trying to figure out how we can get something that is, in the neighborhood of a lot split but that has more protections for consumers and has more protections for cities to make sure that the lot itself can in fact be developed,” Leavitt said.

Supporters included the Master Builders Association of King and Snohomish Counties, Washington REALTORS, the Building Industry Association of Washington and several cities. Josh Friedman, a land-use attorney, told the committee that ULSs are especially helpful for townhouses and other multifamily configurations where unit lots may be smaller than standard single-family lots but were approved together as a project. The mayor of Mercer Island and local government officials said SB 5559 is preferable to competing lot-splitting bills and provides clearer statutory integration with other 2023 housing legislation.

Witnesses urged the committee to work through technical questions — several cities and associations asked for model code, technical clarifications about what happens if a jurisdiction has not yet adopted procedures, and for coordination with other subdivision and lot-splitting bills. No vote was recorded; proponents said SB 5559 clarifies the process and supports middle-housing goals under HB 1110.