October 5, 2018

City proposes changes to encourage more ADUs

The city of Seattle is trying to make it easier to create accessory dwelling units in areas with single-family zoning by removing regulatory barriers in the land use code.

ADUs are small secondary dwelling units that are inside, attached or in the rear yard of a single-family house.

The final environmental impact statement on the proposed changes has been released, and it's at http://www.seattle.gov/council/adu-eis, . The FEIS covers land in all single-family zones that is outside existing urban villages and proposed urban village expansion areas that were studied in the Mandatory Housing Affordability EIS.

Next year, after considering the FEIS alternatives and holding a public hearing, the city council will consider whether to adopt the changes related to ADUs.

Here are the different kinds of ADUs:

• An attached ADU (AADU), or in-law unit or basement apartment, is within or attached to a single-family house

• A detached ADU (DADU), or backyard cottage, is a separate structure in the rear yard of certain single-family-zoned lots

The preferred alternative in the FEIS has these key features:

• Allows two ADUs on one lot

• Removes the off-street parking requirement

• Allows DADUs on lots of at least 3,200 square feet

• Removes the owner-occupancy requirement

• Requires one year of continuous ownership to establish a second ADU

• Allows DADUs of up to 1,000 square feet, the same size currently allowed for AADUs

• Increases DADU height limits by 1-2 feet, with flexibility for green building strategies

• Provides flexibility for one-story DADUs for people with disabilities or limited mobility, with limitations on tree removal

• Establishes a new floor area ratio standard that limits the maximum size of new single-family homes and encourages ADUs

The FEIS estimates that 1,970 ADUs will be produced over the next 10 years under existing regulations and 4,430 under the preferred alternative. It estimates 2,030 single-family homes would be torn down under existing regulations and 1,580 under this proposal.

The document notes that Seattle has about 348,000 housing units. Between 2010 and 2017, the city gained about 40,000 housing units. Based on American Community Survey data, about 44 percent of homes in Seattle are in one-unit detached structures, and most are in single-family zones.

Less than 2 percent of Seattle's roughly 135,000 lots in single-family zones have an AADU.

Since they were legalized citywide in 2010, about 550 DADUs have been constructed or permitted. On average, 69 DADUs have been permitted annually since 2010, with the highest permit volumes in 2016 and 2017 (129 and 118 DADUs, respectively).

This FEIS was prepared under the direction of the city council central staff. The team also included: HDR, lead EIS consultant; ECONorthwest, environmental analysis of housing and socioeconomics; Scarlet Plume, technical editing; Toole Design Group, environmental analysis of transportation, parking, public services and utilities; and Broadview Planning, environmental analysis, and review of the proposal and alternatives.