Accessory Dwelling Units EIS

Final EIS Ruled Adequate & Legislation Adopted

In October 2018, the City issued a Final Environmental Impact Statement (EIS). An appeal of the adequacy of the Final EIS was filed with the City’s Hearing Examiner. The hearing for this appeal concluded on March 29, 2019. On May 13, 2019, the Deputy Hearing Examiner ruled that our environmental review of the proposal to amend the Land Use Code to encourage ADUs adequately explores the potential environmental impacts of the proposal, clearing the way for the City Council to act on legislation. On July 1, 2019, the City Council adopted Council Bill 119544 to amend the Land Use Code to encourage ADUs.

The City proposes to remove regulatory barriers in the Land Use Code to make it easier for property owners to create accessory dwelling units (ADUs) and increase the number and variety of housing choices in Seattle’s single-family zones. Based on a decision from the City’s Hearing Examiner in December 2016, we have prepared an Environmental Impact Statement (EIS) that analyzes how the proposed Land Use Code changes could affect the environment.

Read the Final EIS or our one-page summary.

Final EIS

Draft EIS

Scoping

Background

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 basement apartment, 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.

Final EIS

Published on October 4, 2018, our Final EIS includes a Preferred Alternative for Land Use Code changes to remove barriers to the creation of ADUs. The Preferred Alternative resembles legislation that the City Council will review and consider for adoption. Its key features include:

Allowing two ADUs on one lot
Removing the off-street parking requirement
Removing the owner-occupancy requirement and requiring one year of ownership when creating a second ADU
Modifying development standards that regulate the size, height, and location of DADUs
Increasing the household size limit for a lot with two ADUs
Establishing a new limit on the maximum size of single-family dwellings

The Final EIS identifies and describes potential environmental impacts that could result from removing regulatory barriers to ADU production. For more on the environmental review process, watch our What is an EIS? video and read about the State Environmental Policy Act at the Washington State Department of Ecology website.

ADU Final EIS

ADU Final EIS Appendices

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Appendices

Timeline

Issue Determination of Significance and 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

The Draft EIS was issued on May 10, 2018

Draft EIS Public Comment Period

The Draft EIS comment period closed on June 25, 2018.
The DEIS Public Hearing and Open House was on Thursday, May 31, 2018
Hearing location: Seattle City Hall, 600 4th Ave, Bertha Knight Landes room.
Hearing Handout Display Boards Watch Public Comment

Prepare Final EIS

The Final EIS addresses comments received during the comment period

Issue Final EIS

The Final EIS was issued on October 4, 2018

City Action

On May 13, 2019, the Deputy Hearing Examiner ruled that our environmental review of the proposal to a encourage ADUs adequately explores the potential environmental impacts of the proposal, clearing the way for the City Council to act on legislation. The ADU proposal will be discussed at the following upcoming meetings of the Sustainability & Transportation Committee. All meetings will be held in the City Council Chambers, 2nd floor, Seattle City Hall, 600 Fourth Avenue.

Study Area

Draft EIS

The Draft EIS comment period closed on June 25, 2018. The information in the Draft EIS was provided for review and comment by interested parties and helped us prepare the Final EIS, which includes responses to all substantive comments received during the Draft EIS public comment period.

The Draft EIS analyzed three alternatives. Alternative 1 (No Action) assumes that the City makes no changes to the Land Use Code related to ADUs. Alternatives 2 and 3 assume implementation of Land Use Code changes. Both action alternatives address regulations and policies frequently cited as barriers to creation of ADUs. Alternatives 2 and 3 differ in the scale and focus of the proposed changes. Alternative 2 represents a broad range of changes to the Land Use Code, similar to the draft proposal analyzed in May 2016 prior to the Hearing Examiner’s decision. Alternative 3 considers more modest adjustments to the Land Use Code that emphasize maintaining the scale of existing development in single-family zones.

		Alternative 1 (No Action)	Alternative 2	Alternative 3
1	Number of ADUs allowed on lots in single-family zones	Lots in single-family zones can have one AADU or one DADU, but not both.	Lots in single-family zones can have an AADU and a DADU.	Lots in single-family zones can have an AADU and a DADU or two AADUs.
2	Off-street parking requirements	One off-street parking space is required for an AADU or a DADU unless the lot is in an urban village.	No off-street parking required.	No off-street parking required for lots with one ADU. One off-street parking space is required for lots adding a second ADU.
3	Owner-occupancy requirements	An owner must occupy either the main house or the AADU/DADU 6 months a year.	No requirement for an owner to occupy the house, AADU, or DADU.	No change from Alternative 1 (No Action).
4	Minimum lot size	4,000 square feet	3,200 square feet
5	Maximum gross floor area	AADU 1,000 square feet, including garage and storage areas. DADU 800 square feet, including garage and storage areas.	AADU 1,000 square feet, excluding garage and storage areas. DADU 1,000 square feet, excluding garage and storage areas. An AADU or a DADU may exceed 1,000 square feet if the portion of the structure in which the ADU is located existed on December 31, 2017, and if the entire ADU is located on one level.	AADU 1,000 square feet, including garage and storage areas. DADU 1,000 square feet, including garage and storage areas. An AADU may exceed 1,000 square feet if the portion of the structure in which the AADU is located existed on December 31, 2017, and if the entire AADU is located on one level.
6	Maximum height	No change from existing height limits, which vary by lot width and range from 15 to 23 feet.	Height limits are 1 to 3 feet higher than existing limits, depending on lot width. Allow 1 to 2 additional feet for a DADU that meets green roof standards.	Height limits are 1 to 3 feet higher than existing limits, depending on lot width.
7	Lot coverage	No change from current regulations. Lots greater than 5,000 square feet 35 percent of lot area. Lots less than 5,000 square feet 15 percent of lot area plus 1,000 square feet.
8	Rear yard coverage	40 percent of a rear yard can be covered by a DADU and other accessory structures (like a garage). This limit applies in addition to the overall lot coverage limit.	60 percent of a rear yard can be covered by a DADU and other accessory structures, if the DADU is 15 feet or less in height. Rear yard coverage for structures other than a DADU cannot exceed 40 percent.
9	Roof features	No exceptions for roof features on accessory structures are allowed.	Height limit exceptions are allowed for projections like dormers that add interior space, subject to the provisions applicable to single-family houses.
10	Location of DADU entry	DADU entrances cannot face the nearest side or rear lot line unless that lot line abuts an alley or other public right of- way.	DADU entrances can be on any façade if they are 10 feet from the lot line and if located on the façades facing the nearest side or rear lot line (unless abutting right-of-way).
11	Maximum household size	Any number of related people, or up to eight unrelated people, can live on lots in single-family zones including in an AADU or a DADU.	Any number of related people, or up to eight unrelated people, can live on lots in single-family zones with an AADU or a DADU. If the lot has an AADU and a DADU, the limit is 12.	No change from Alternative 1 (No Action).
12	MHA requirements	Mandatory Housing Affordability (MHA) does not apply to creation of ADUs on lots in single-family zones.	No change from Alternative 1 (No Action).	MHA requirements apply when a property owner applies for a permit to construct a second ADU on a lot that already has one ADU. For development of a second ADU, the MHA requirements for zones with an (M) suffix would apply, as outlined in Section 23.58C of the Land Use Code. For purposes of analysis, this equates to an affordability contribution of $13 per square foot of gross floor area in the second ADU.
13	Predevelopment costs	No change.	Reduces predevelopment costs by 10 percent. This could result from reducing permitting costs by streamlining project review, reducing permitting and design costs by providing pre-approved plans, or other actions.	No change from Alternative 1 (No Action).
14	Maximum floor area ratio (FAR) limit	No FAR limit for single family zones. The maximum size for the main house is effectively set by the yard requirements, height limit, and lot coverage limit. ADUs are subject to the maximum size limits described above.	No change from Alternative 1 (No Action).	New construction FAR limits apply to development in single-family zones. New houses (i.e., principal structures) are subject to a FAR limit of 0.5 or 2,500 square feet, whichever is greater. Below-grade floor area and floor area in DADUs is exempt. ADU size limits apply. Existing houses Existing lots in single-family zones exceeding the FAR or 2,500-square-foot limits can convert existing space to an AADU and add a DADU subject to the size limit above.

Draft EIS

Draft EIS (Full Document - 52 MB)

Draft EIS Appendices

Accessory Dwelling Units EIS

Final EIS Ruled Adequate & Legislation Adopted

What is an ADU?

Final EIS

Appendices

Timeline

Study Area

Draft EIS

Draft EIS

Scoping

Background

Mike O'Brien

Citywide Information

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