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Des Moines council adopts ADU ordinance to comply with state law, removes owner-occupancy and limits fees
Summary
The city adopted Ordinance 25-056 to align accessory dwelling unit (ADU) rules with 2023 state law (HB 1337): no owner-occupancy requirement, a 3-ADU-per-lot limit, a size cap of 1,200 sq ft, and reduced impact-fee treatment.
The Des Moines City Council voted unanimously at its June 12 meeting to adopt Ordinance 25-056, amending municipal code to conform to Washington’s 2023 accessory dwelling unit law (House Bill 1337) and implementing local standards.
Under the ordinance the city will not require owner occupancy for properties with ADUs (removing an earlier local requirement). The code permits up to three ADUs on a lot in any configuration (attached or detached) and establishes ADU size between 350 square feet and 1,200 square feet. The ordinance also aligns impact-fee policy with state rules so cities may charge up to 50% of impact fees for an ADU compared with the principal unit. Parking requirements follow the recently enacted state guidance: no parking required for residential units under 1,200 sq ft.
Community Development Director Rebecca Deming summarized the changes as required by state law and reviewed staff’s recommended code-language adjustments. The council amended the staff motion to refine the ordinance language (staff replaced a subjective “consistent and complementary” design line with: “the ADU shall be complimentary with the architectural style and materials of the primary residence; components considered include materials and roof line”) and then adopted the ordinance.
No public comments were made during the ADU public-hearing segment. Councilmember Nutting moved approval with the amendment; the motion passed 7-0.
City staff said the ordinance allows conversions of existing accessory structures and permits condominium sales of ADUs subject to subdivision or condominium requirements. Staff noted the Federal Way example used for student-generation analysis later in the meeting, but the ADU ordinance itself does not change school-district authority over capacity or enrollment.
Councilmembers discussed design guidance and asked staff to provide clearer, non-subjective guidance about factors to consider when reviewing the design of an ADU — for example, roof line and exterior materials — and asked staff to explore a city pre-approval program for commonly used ADU plans.
Ordinance 25-056 is effective immediately as the city brings local code into compliance with state law; staff will return with administrative guidance and outreach materials to help property owners and local builders understand the new rules and permit pathways.
