Encouraging Backyard Cottages

What's Happening Now?

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.

Pre-approved DADU plans
Our gallery of pre-approved designs for backyard cottages is now live. 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.

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.

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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.

Timeline

  • 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 2019, we invited architects and designers to submit DADU plans that the City could pre-approve. 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

Reports