Accessory Dwelling Units EIS

Thanks for your suggestions about what to consider in our study.

We summarized the comments received, and described how we are considering those comments, in the scoping report.

The City of Seattle is proposing to change regulations in the Land Use Code to remove barriers to the creation of accessory dwelling units (ADUs) in single-family zones. The proposal involves allowing two ADUs on one lot, removing the existing off-street parking and owner-occupancy requirements, and changing some development standards that regulate the size and location of detached ADUs.

ADUs have been allowed citywide as part of a single-family house or in the backyard of a single-family-zoned lot since 1994 and 2010, respectively. The City’s action would modify the rules that regulate when and where a property owner can create an ADU. The objectives of this action are to

  • Remove regulatory barriers so it's easier for property owners to permit and build ADUs and backyard cottages
  • Increase the number and variety of housing choices available in single-family zones
  • Encourage creation of small-scale, family-friendly homes affordable to a range of households and flexible for their changing needs

These policy changes would affect development in Seattle’s single-family zones.

Based on a decision from the City’s Hearing Examiner in December 2016, we are preparing an Environmental Impact Statement (EIS) that will analyze three alternatives and identify the impacts of each alternative.

Get Involved

We are now preparing the Draft EIS. After we issue the Draft EIS, there will be a public comment period and opportunities to provide verbal and written comment. 

Questions? Contact the project team at


What is an ADU?

ADUs are small secondary dwelling units inside, attached to, or in the rear yard of a single-family house. An attached ADU (AADU), often called an in-law unit or a granny flat, is contained within or attached to a single- family house. A detached ADU (DADU), often called a backyard cottage, is a separate structure allowed in the rear yard of certain single-family-zoned lots. DADUs can be new structures or created through conversion of an existing structure, like a garage.

What is an EIS?

An EIS is a tool to inform decision makers about the positive and negative effects of a proposal. The proposal might be a project, like construction of a new building or road, or a new policy or plan that could affect the environment. Washington’s State Environmental Policy Act (SEPA) requires Environmental Impact Statements so that the public, tribes, and other public agencies can help identify a proposal’s environmental impacts, as well as strategies for reducing or avoiding them. Decision-makers can then approve, modify, or deny the proposal as appropriate.

Study Area

Map of the ADU EIS study area


Issue Determinaton of Significance & Scoping Notice
Determination of Significance and Scoping Notice for the ADU EIS was issued on
October 2, 2017
Conduct SEPA Scoping
The scoping comment period will close at 5:00 p.m. on
November 1, 2017
Extended to November 16, 2017
Prepare Draft EIS
Scoping comments will be reviewed and the Draft EIS will be prepared
Issue Draft EIS
Tentative issuance Spring 2018
Draft EIS Public Comment Period
A 30-day comment period will follow the issuance of the Draft EIS and will include a public hearing
Prepare Final EIS
The Final EIS will address comments received during the comment period
Issue Final EIS
Tentative issuance Summer 2018
City Action
The City Council will vote on proposed legislation to amend the Land Use Code


From October 2 to November 16, we took input on what we should study in the EIS. This scoping period included two public scoping meetings on October 17 and 26 at the High Point Community Center and Hale’s Ales. We summarized the comments received, and described how we are considering those comments, in the scoping report.

Watch a video presentation about the scoping process:


Scoping Report Summary of the comments received, and description of how we are considering those comments. All comments received are included in the appendices.

Scoping Handout Describes the initial scope and alternatives distributed for feedback during the scoping comment period.

Scoping Meeting Boards Information presented at the two Public Scoping Meetings

Presentation from 10/17 and 10/26 Public Scoping Meetings