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City Launches Effort to Develop Pre-approved Plans for Accessory Dwelling Units

Today, the Seattle Department of Constructions and Inspections (SDCI) and Office of Planning and Community Development (OPCD) together are launching a survey to help guide our effort to select designs for pre-approved plans for accessory dwelling units (ADUs).

Small, secondary homes located on the same lot as an existing residence, ADUs create more places to rent in neighborhoods where housing is often unaffordable and give homeowners flexibility to generate income, build wealth, and meet their changing household needs. Since 2010, Seattle has allowed detached ADUs (DADUs), often called backyard cottages or carriage houses, in our single-family zones. Yet only a small share of eligible lots have an ADU.

In recent years, we’ve been identifying the barriers that keep us from having more of this housing type. In July 2019, the City passed legislation eliminating many common regulatory barriers that discourage or prevent people from creating an ADU. Now, we’re addressing other challenges so that more people can own and rent these homes.

To simplify and streamline permitting, we’re working with architects, designers, and builders to develop pre-approved DADU construction plans that offer a faster, easier, and more predictable design and permitting process for Seattle residents. Homeowners choosing a pre-approved DADU plan pay a reduced permit fee and get their permit faster — in 2-6 weeks, compared to 4-8 months for a typical DADU permit. In certain situations, such as lots with protected trees or Environmentally Critical Areas (ECAs), the pre-approved DADU plan timeline could vary.

As a first step, we invite you to share your input on how we should choose DADU plans to pre-approve. Through October 21, take our survey to shape the criteria and design principles we will encourage in our selection. Later this fall, we’ll publish our selection criteria and announce a call for submissions. Selected plans will be reviewed, pre-approved, and displayed in an online gallery. To use a pre-approved plan, a homeowner pays a small royalty to the designer, who can help prepare the site plan necessary to get a construction permit. More details on this process are coming soon.

Want to learn more? On October 19, OPCD and other departments will be attending ADU Fair: Resources for creating accessory dwelling units, a free event at Southside Commons from 2:00 to 5:00 p.m. Come by to learn about ADUs, talk with staff, or even take our survey. You can also email us at, read our summary, and visit the SDCI website on ADUs.