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Capitol Hill Community Post | Seattle evaluates options to encourage backyard cottages, in-law apartments

From the Seattle Office of Planning and Community Development

The City of Seattle continues to seek public input on the environmental review of options to encourage the development of more in-law apartments and backyard cottages that would allow for more rental housing in the city’s single-family zones.

The review evaluates a proposal advanced by Councilmember Mike O’Brien that aims to remove regulatory barriers and make it easier for property owners to build Accessory Dwelling Units (ADUs).

Current City ordinances allow two types of ADUs: in-law apartments inside a single-family home and detached backyard cottages. Seattle homeowners have created 1,591 in-law apartments and 579 backyard cottages since first allowed in 1994 and 2010, respectively. Homeowners received permits to build 263 ADUs last year.

The potential policy changes analyzed through the environmental review process would increase rental housing options in areas where housing is unaffordable to most households. Since 2016, Seattle has been the city with the fastest growing single-family home prices in the nation, with the cost of the average single-family home now $820,000.

Under Seattle’s current zoning, approximately 7400 acres allow for multifamily, commercial, and mixed-use buildings, while 21,000 acres are zoned exclusively for single-family homes. There are roughly 135,000 lots in Seattle’s single-family zones.

Citywide, the rapid pace of construction in 2017 added 8,730 net new homes, most of which were apartments and townhomes. Last year, 88 percent of all new homes were built in Seattle’s urban villages. The number of detached single-family homes in Seattle remained essentially unchanged.

Three options studied

Under current regulations governing ADUs, the homeowner must live on the property, only one ADU is allowed per lot, and the property must include two parking spaces, one for the main home, and one for the ADU.

The City’s Draft Environmental Impact Statement (DEIS) released on May 10th studies three alternatives for Land Use Code changes related to ADUs:

  • Alternative 1: no action; current rules maintained.
  • Alternative 2: one in-law apartment and one backyard cottage allowed on the same lot; parking no longer required for ADUs; the homeowner may live elsewhere.
  • Alternative 3: two ADUs allowed per lot (either two in-law apartments or one apartment and one cottage); an additional parking space is required only if two ADUs are built.

Alternatives 2 and 3 both reduce the minimum lot size required to build an ADU from 4000 square feet to 3200 square feet. Both action alternatives allow for slightly larger cottages and apartments than the no action alternative.

Alternative 3 also explores the option to include a size restriction on new single-family homes by implementing a floor area ratio limit. Today, the size of single-family homes is limited only by yard requirements, height limits, and lot coverage limits.

The no action alternative anticipates homeowners would build 1,890 ADUs by 2027. Alternatives 2 and 3 would both result in an increase in ADU construction in the next decade: 3,330 and 3,100 total new ADUs, respectively.

The Draft EIS was developed jointly by the Seattle City Council’s Central Staff and the Office of Planning and Community Development (OPCD). In December 2016, the Seattle Hearing Examiner ruled that a full EIS on Councilmember O’Brien’s proposal was required before changes could be adopted.

The Draft EIS identifies environmental impacts and mitigation measures for each alternative. Based on public comments during the public scoping phase in the fall of 2017 and direction from the Hearing Examiner, the analysis includes possible impacts related to housing and socioeconomics, land use, aesthetics, parking and transportation, and public services and utilities.

The City is now seeking public comment on the adequacy of this environmental review. A public comment period will end at 5:00 p.m. on June 25, 2018. The public can comment on the DEIS online at or by email to

The City will also hold an open house and public hearing at 5:30 p.m. on May 31, 2018 in the Bertha Knight Landes room at Seattle City Hall, where people may make verbal comments.

The City’s Final EIS and a preferred alternative of policy changes will be developed based on community comments already received and input on the three alternatives in the DEIS. Council Central Staff expects to complete the Final EIS in September before draft legislation is developed for the City Council’s consideration.

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8 thoughts on “Capitol Hill Community Post | Seattle evaluates options to encourage backyard cottages, in-law apartments

  1. The things that they waste their time on… what’s the ROI they’re going to get on this…slim and none, most likely. They should focus more on smartly rezoning areas that would benefit from more density.

    • Not to mention fewer older people close to or already retirement age being forced out of their homes due to incessant property tax levies. People on fixed retirement incomes are squeezed with every property tax hike. An ADU means fewer people might have to sell their homes and move out of Seattle.

      • I seriously doubt that this plan helps retirees to stay in their homes. Adding legal livable units will cost tens of thousands in initial outlays. If a retiree or other homeowner is struggling financially, he/she will probably not have the extra funds to spend. Alsom the timeline before the construction costs are covered by rent will be too long for older residents.

      • Agreed with Jim. This could be a huge win for these folks. They may not have a lot of disposable income but they most certainly have a lot of equity.

        A HELOC of 80k and take in 1,500 a month for rent means in several years their loan is paid, then they are taking in a nice monthly income to sustain them in their homes.

      • Alternatives two allows the building of ADUs and MILs even if the owner doesn’t live on the property. Alternative one proposes no changes. It isnt clear if alternative three would require the homeowner remain on the properrty, but I suspect it does not.

        If you want to liberalize the regs and encourage ADUs just remove the parking requirement. Allowing two ADUs or MILs and removing the residency requirement really directs these changes to investors, who will then purchase single family homes and turn them into triplexes. If you support that, fine, but please don’t focus on poor old folks when it is obvious the legislation is intended to benefit an entirely different group.

  2. I’d love to see more backyard cottages allowed! Great way to infill and increase rental supply.

    Preferable if they do not call for any parking requirements and if trees need to be removed, replacements are required to be planted on the property. I’d hate to see our urban canopy shrink over this.

  3. Portland has done this successfully, with very tasteful backyard cottages that preserve historic homes that would otherwise be demolished to increase density. Seattle, look to your neighbor for a great example.