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Ultimate Guide To Backyard Cottages In Seattle



|Last Updated: 27 Jul 2021

Backyard Cottages generally include a living room, sleeping area, kitchen, and bathroom and have a lockable entrance door.


A Backyard Cottage or a DADU is a small residential structure sharing the same lot as a house, but self-contained and physically separate from the primary house. In the Seattle Municipal Code (SMC) zoning provision, Backyard Cottages are referred to as “Accessory Dwelling Units, detached.” They are also sometimes referred to as detached accessory dwelling units, granny flats, mother-in-law apartments, and carriage houses. On some lots, a Backyard Cottage may be located in a side yard.




Because of their small scale, Backyard Cottages can create attractive and affordable rental opportunities for Seattle residents without changing the neighborhood or quality of life for other residents. They can provide greater financial flexibility for homeowners by letting them collect rent for a portion of their existing property or help accommodate larger or multi-generational families. Backyard Cottages also offer a new housing type to Seattle that is desirable, quiet, and compatible with other homes in single-family neighborhoods.


Backyard Cottages provide a surprising number of benefits to communities, homeowners, and renters. Although much of the attention given to Backyard Cottages revolves around their potential for increasing the supply of affordable housing opportunities, Backyard Cottages may also help to address other social issues, particularly those relating to housing options for the growing elderly population.




In December 2009 Seattle City Council adopted legislation to allow the construction of backyard cottages on eligible lots in single-family zones throughout the city. Before the December 2009 legislation, Backyard Cottages were permitted only in Southeast Seattle, where they were authorized by legislation in 2006.




  • You can build a Backyard Cottage if you meet the following requirements: You are a homeowner.
  • Your property is located in a single-family residential zone (SF 5000, SF 7200, or SF 9600 zoned area).
  • Your lot is not in a Shoreline District.
  • Your lot is at least 4,000 square feet in area.
  • You or your property co-owner(s) will occupy either the main house or the Backyard Cottage as a permanent and principal residence.
  • You or your property co-owner(s) plan to live in the main home or the Backyard Cottage for more than six months of each calendar year.
  • You or your property co-owner(s) who live on the property have a 50 percent or greater interest in the property.




If your property is large enough for a Backyard Cottage there are a variety of other issues you will need to think about. Consider the following:

  • Even if your lot is 4,000 square feet or greater, do you have extra space to spare?
  • How will your lot and neighborhood look with a Backyard Cottage?
  • How can the design of the Backyard Cottage maintain your privacy and that of your neighbors?
  • Will you rent the unit? Who is your potential renter and how can you build the unit to meet the demands of your rental market?
  • Do you have time to care for an additional unit?
  • Converting a detached garage might save money. Can you convert an existing detached garage into a Backyard Cottage?
  • Besides exterior and interior work, are you prepared for the cost and disruption of extending the sewer, water, and electrical connections?
  • Do you want to have separate utility meters?
  • How will your tenants access the Backyard Cottage? Can you use a side yard or alley for this purpose?
  • Will you need to hire professionals to help you design and build the Backyard Cottage?




The City of Seattle has specific development standards for Backyard Cottages. These standards are intended to make Backyard Cottages work with the city’s small lots and compact neighborhoods, allowing additional housing that does not seem intrusive in an established neighborhood of single-family homes. You and your design professional will need to review the standards to design your backyard cottage.

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