Encouraging Backyard Cottages

What's Happening Now?

2022 ADU Annual Report

In March 2023 we published our 2022 ADU Annual Report, which includes new information about ADU production in Seattle. In 2022, 988 ADUs were permitted, the highest annual total in the city’s history and a fourfold increase over 2018, the last year before Seattle adopted new rules for ADUs in 2019. As required by Ordinance 125854, the report offers data on the number of ADU permits issued, where they are located, and how they are configured. It reports on the use of our pre-approved DADU plans and evaluates how ADUs are used as short-term rentals and sold as condominium units. We also share results from a survey of ADU owners and occupants that help us understand who is benefitting most from the opportunity to create or live in an ADU and what barriers exist to greater and more equitable ADU development. 


Our new ADUniverse website launched in September 2020. ADUniverse features a gallery of pre-approved DADU designs, a step-by-step guide to the ADU process, and a search tool to identify the feasibility of adding an ADU to your property. An interactive version of the 2021 ADU Annual Report is also available.

Pre-approved DADU plans

View our gallery of pre-approved designs, created by local designers and architects. These 10 building plans offer a faster, easier, and more predictable permitting process for creating a DADU. In most cases, you can get your permit in just 2-6 weeks. For background on this initiative, read our submission guidedesign criteria survey, and one-pager.

Interested in creating an ADU? 

Start with SDCI's updated tip sheets:

Seattle's ADU reform

In July 2019, Mayor Jenny Durkan signed legislation to remove regulatory barriers and make it easier for property owners to create accessory dwelling units (ADUs) in Seattle's single-family zones. The new ADU regulations took effect on August 8, 2019.

In addition to signing the most progressive ADU ordinance of any U.S. city, Mayor Durkan also issued an Executive Order to implement several additional strategies to help more people be able to own and rent ADUs, including:

  • Assisting homeowners in the ADU design and permitting process
  • Piloting strategies to support equitable ADU development and affordability for homeowners and tenants
  • Convening a workgroup to advise on City ADU programs and services
  • Monitoring ADU production continually to evaluate the benefits and effects 

What is an ADU?

Accessory dwelling units (ADUs) are small, secondary dwellings allowed in residential zones:

  • A detached accessory dwelling unit (DADU), often called a backyard cottage or carriage house, is an ADU located in a separate structure from the principal dwelling unit (i.e., the main house).
  • An attached accessory dwelling unit (AADU), often called an in-law apartment or basement suite, is an ADU located within or attached to the main house.

Tell Us Your Story

Have you built or considered building an ADU? Do you have ideas for how the City can help more people create, rent, and live in ADUs? We would love to hear from you. Please contact Nick Welch at nicolas.welch@seattle.gov to share your experience.


  • The City of Seattle has allowed attached ADUs and detached ADUs in all single-family zones since 1994 and 2010, respectively.
  • To encourage more of this housing type, in 2014 the City Council adopted Resolution 31547 directing us to explore changes that could make them easier to build and allow them on more lots in Seattle.
  • In May 2019, the City's Hearing Examiner upheld our environmental review of the proposal, clearing the way for legislative action on a proposed ordinance.
  • In July 2019, the Council adopted and Mayor Durkan signed legislation removing regulatory barriers to ADU production. The Mayor also issued an Executive Order calling for additional strategies to encourage ADUs for all.
  • In February 2020, we invited architects and designers to submit DADU plans that the City could pre-approve based on criteria in our submission guide. After receiving and reviewing more than 160 submissions, we selected and pre-approved 10 DADU plans that offer residents a streamlined design and permitting process.
  • In September 2020, we launched ADUniverse, a new resource for Seattle residents that features our pre-approved plans, a step-by-step guide for prospective ADU owners, and a search tool to help homeowners assess the feasibility of adding an ADU on their property.

ADU Legislation

In July 2019, Mayor Jenny Durkan signed legislation to remove regulatory barriers and make it easier for property owners to create accessory dwelling units (ADUs) in Seattle's single-family zones. The new ADU regulations took effect on August 8, 2019.

Environmental Impact Statement

SEPA draft legislation

Community Meetings

City Council Meetings


Planning and Community Development

Rico Quirindongo, Director
Mailing Address: P.O. Box 94788, Seattle, WA, 98124-7088
Phone: (206) 386-1010

The Office of Planning and Community Development (OPCD) develops policies and plans for an equitable and sustainable future. We partner with neighborhoods, businesses, agencies and others to bring about positive change and coordinate investments for our Seattle communities.