Seattle updates zoning laws to facilitate accessory dwelling unit development

The Seattle City Council Select Committee on the Comprehensive Plan convened on April 16, 2025, to discuss significant updates regarding accessory dwelling units (ADUs) and residential density regulations. The meeting highlighted the city's ongoing efforts to enhance housing options and streamline development processes.

One of the key points discussed was that ADUs are not included in the maximum floor area ratio (FAR) calculations for properties. This means homeowners can construct ADUs even if they have already reached the density limits for their primary dwelling. Additionally, the city has eliminated the requirement for street improvements when adding an ADU, making it easier for property owners to expand their living spaces.

The committee also noted that detached ADUs can be built in rear yards without the need for parking spaces. To further support homeowners, the city has developed pre-approved designs for ADUs, allowing property owners to submit plans to the Seattle Department of Construction and Inspections with confidence that they will meet permit requirements.

In line with House Bill 1110, the city is mandated to increase residential development density on lots. Density is assessed through two primary methods: the number of units allowed per lot and the square footage permitted per unit. For example, a 5,000 square foot lot can accommodate up to four units based on a density limit of one unit per 1,250 square feet.

The meeting also addressed the current zoning regulations under Council Bill 120969, which stipulate minimum lot sizes for various residential zones. These range from one unit per 9,600 square feet in the least dense zones to one unit per 2,000 square feet in small lot residential areas. The council discussed provisions that allow for flexibility in smaller lot sizes, enabling development in areas that do not meet the minimum requirements.

Overall, the discussions at the meeting reflect Seattle's commitment to increasing housing availability and adapting zoning laws to facilitate more diverse residential options. The next steps will involve further refinement of these regulations to ensure they effectively meet the city's housing needs.