Seattle Enacts ADU Legislation

The Seattle City Council voted unanimously to allow the construction of more and larger accessory dwelling units (ADUs) in all neighborhoods while removing requirements that property owners live on site and provide off-street parking.

Two ADUs will now be allowed on each lot, either two attached ADUs or one attached ADU and one detached ADU. The maximum DADU size will increase from 800 to 1,000 square feet and the minimum lot size for DADUs will be reduced from 4,000 to 3,200 square feet. The legislation will also cap the size of any newly constructed house, whether it has an ADU or not, to 2,500 square feet or a floor-area-ratio (FAR) of 0.5, whichever is greater. The square footage of any ADUs are not counted in the FAR limit.

In addition, the legislation eliminates the city’s requirement to provide off-street parking spaces.

Two amendments were approved prior to final passage: one grants an additional 35 square feet of floor space for bicycle storage and the second directs the city to study the use of ADUs as short-term rentals and states the Council’s intent to restrict such use if it is “excessive.” An amendment by Councilmember Lisa Herbold to require one year of property ownership before a second ADU could be built was defeated 7-1.

Mayor Durkan signed the legislation on July 9, and it will take effect on August 8 – with the exception of the FAR limits for single family homes, which will not go into effect until March 1, 2020.

AIA Seattle’s Housing Task Force supported this legislation with technical comments, meetings with legislators and staff, an ADU tour and more. Special thank yous to Matt Hutchins AIA, Sheri Newbold AIA and Karen DeLucas AIA for your advocacy.

July 2019