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.

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

Scoping 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. Scoping Report

Scoping Comments

Scoping Handout

Scoping Meeting Boards

Scoping Meeting Presentation Watch a video presentation about the scoping process: