Councilmember O’Brien Celebrates Council Vote to Ease Restrictions on Backyard Cottages

Home » Councilmember O’Brien Celebrates Council Vote to Ease Restrictions on Backyard Cottages

Councilmember Mike O’Brien (Dist. 6, Northwest Seattle), chair of the Sustainability & Transportation Committee, and his Council colleagues unanimously passed an ordinance today that reduces the barriers to building backyard cottages across the city in an 8-0 vote. 

“I am thrilled that after years of work and legal delays, Seattle residents will have an easier time building backyard cottages and in-law units, creating more housing options in Seattle neighborhoods,” O’Brien said. “I’ve had dozens and dozens of Seattle families reach out to my office asking the City to loosen restrictions for backyard cottages. People have been chomping at the bit to build housing options that fit their families, whether it is an in-law unit for an aging parent, a backyard unit for a college-aged child, or a space to rent to a neighbor. We’re in a housing crisis and need every tool to create a more affordable and equitable Seattle. For years, density has been declining in single-family areas. These neighborhoods were originally designed to accommodate more people. This legislation creates modest but meaningful changes to provide flexible, affordable housing options for families, homeowners, and renters while still preserving the look and feel of single-family neighborhoods.”

“This long-awaited legislation is smart policy that’s responsive to our affordability and climate crises,” said Councilmember Teresa Mosqueda (Position 8, Citywide), Chair of the Housing, Health, Energy and Workers’ Rights Committee. “By reducing barriers to more diverse housing choices across the city, we can right historic wrongs that led to exclusionary zoning in our neighborhoods and correct course to advance a greener, denser, and more affordable Seattle. ADUs and DADUs provide opportunities for multigenerational housing, help us decrease our environmental and carbon footprint, and provide some homeowners with a way to stay in their homes and age in place—an important benefit as the cost of living rises in Seattle. This is one meaningful step that will generate gentle infill housing options, but much more must be done to create the density we need to accommodate our growing city.”

The legislation, sponsored by Councilmember O’Brien:

  • Increases the allowed size of backyard cottages from 800 square feet to 1,000 square feet.
  • Adds an additional 1-2 feet in height, allowing for more usable space in the units’ interiors.
  • Allows two accessory dwelling units (ADUs) on a property instead of one.
  • Limits the floor area ratio of new homes, encouraging homeowners to build both a basement unit and a backyard unit while maintaining the character of the main home. This also discourages teardowns of older homes and the building of expensive “McMansions.”
  • Eliminates the rule that a property owner has to live somewhere on site.
  • Removes the off-street parking requirement, potentially lowering the total cost of building new ADUs.

Overall, these changes are expected to incrementally increase the backyard cottage supply by 2,400 units over 10 years, creating about 4,400 ADUs altogether, while simultaneously decreasing the expected number of teardowns of existing homes by 450 over the same timeframe.


Attached Accessory Dwelling Units (AADUs like garden apartments, basement suites and in-law suites) and Detached Accessory Dwelling Units (DADUs like backyard cottages and carriage houses) have been allowed citywide since 1994 and 2010 respectively.

From 2014 to 2016, Councilmember O’Brien chaired the land use committee where he worked to identify land use strategies to address housing affordability. The Seattle City Council has considered amending rules around Accessory Dwelling Units since 2014, when the Council adopted Resolution 31547

For more information on Accessory Dwelling Units, visit Councilmember O’Brien’s website

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