Mountlake Terrace planning commissioners review middle-housing rules, ADU limits under new state law

Mountlake Terrace planning commissioners spent their March 10 meeting focused on draft development-code changes and the city’s housing action plan aimed at implementing recent Washington state middle-housing and accessory-dwelling-unit (ADU) laws.

The meeting, convened by Chair Bautista, featured consultants from Methune and Echo Northwest presenting code options and asking the commission for direction on what housing types to allow, how to measure and incentivize density, and how to protect trees and neighborhood character while meeting state requirements such as those in House Bill 1110 and House Bill 1337. Commissioners did not take any formal votes.

Why it matters: the state law requires jurisdictions to allow more middle-housing types and to permit ADUs under new minimums and it sets deadlines that the city must meet. The commission’s decisions will shape how new housing can fit into existing Mountlake Terrace neighborhoods, affecting site layout, parking, tree canopy and the visual scale of infill development.

Presenters told commissioners the city already rezoned residential neighborhoods into four new R zones under the comprehensive plan and now must adopt matching development standards. Consultant Heidi Oian of Methune said the team will both draft code and run “test fits” to check how different standards play out on typical Mountlake Terrace lots. “I am Heidi Oian. I’m a partner at Methune. I practice both architecture and urban design,” Oian told the commission as she outlined model-code approaches from Tacoma, Spokane, Seattle and Portland.

Commissioners debated which housing types to encourage. Vice Chair Betscher said she objects to townhouse developments whose “entire ground plane is taken up by cars” and called for site layouts that prioritize usable open space and better relationships between buildings and the street. Commissioner Stinson and others said cottage-style and courtyard apartments tested well in past public outreach and could provide more-affordable ownership opportunities if they “pencil out” economically.

Several commissioners and staff pressed for clear ways to protect tree canopy, reduce curbside clutter from multiple refuse cans on trash day, and avoid parking spillover onto neighborhood streets as density increases. Staff noted existing concerns in recent developments where waste containers are placed at the curb rather than centralized on site, creating dozens of receptacles on collection days.

On ADUs, presenters summarized constraints from state law: jurisdictions must allow at least two ADUs on a lot; code may set a local maximum but must allow a minimum ADU size up to 1,000 square feet (local code may allow up to 2,000 square feet). Presenters also quoted state parking rules discussed by the consultants: no parking requirement within one-half mile of transit, a limit of one required stall for lots under 6,000 square feet and up to two required stalls for lots larger than 6,000 square feet. As Heidi Oian said during the presentation, “You have to allow at least 2 ADUs on any lot.”

Commissioners also discussed what measurement tools to use to control scale — floor-area ratio (FAR), lot coverage, maximum building widths or a combination. Some commissioners said FAR would be useful for targeted incentives (for instance, allowing more floor area in exchange for tree retention or on-site stormwater treatment). Others worried FAR plus existing rules could overcomplicate the code and preferred simpler lot-coverage and story limits unless test fits show a need to use FAR.

Several commissioners expressed concern about condominiumization and the administrative burdens that come with separating ownership interests on formerly single-family lots. Staff said the city must allow the state-authorized uses but can still use design, setback and streetscape standards to moderate local impacts.

No formal actions were taken. Consultants and staff described immediate next steps: consultants will begin feasibility testing and “test fits” on typical lot types starting the day after the meeting; the project team will conduct developer interviews and technical stakeholder outreach; the city will hold a community open house on March 26 at City Hall to collect broader public input; staff and consultants plan to return with draft code and test-fit visuals in mid-April. The consultants and staff outlined a draft schedule that includes a Planning Commission adoption hearing tentatively on May 26 and a City Council adoption target of June 12 to meet state compliance timelines.

Commissioners voiced differing preferences: some favored targeted housing-type design standards to produce predictable outcomes, while others preferred a more flexible, zone-based approach. Multiple commissioners supported incentives for tree retention, stormwater treatment, pedestrian connectivity and community-facing ground-floor uses — with staff and commissioners cautioning against allowing developers to claim a public benefit while effectively privatizing ground-floor space.

The commission asked staff and the consultant team for real-world test fits using Mountlake Terrace lot sizes and to report feasibility results that show which housing types are economically plausible. The project returns to the commission for a shorter briefing in two weeks on the housing action plan and the development-code process, followed by additional workshops and stakeholder outreach through May and June.

What’s next: Methune and Echo Northwest will complete test fits and an economic feasibility analysis, staff will launch public noticing and the March 26 open house, and the project team will return with draft code recommendations for further commission review in April. There were no votes or formal code changes adopted at the March 10 meeting.