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. Backyard Cottages generally include a living room, sleeping area, kitchen, and bathroom and have a lockable entrance door.
To simplify and streamline DADU permitting, in 2020, the City of Seattle developed pre-approved DADU plans that allow Seattle residents to permit their own lower-cost, space efficient homes, in a quick time frame of 2-6 weeks.
These DADUs are up to 1,000 sf and can be used for so many different purposes. Used as a rental unit, guest house, home office, or personal sanctuary, people throughout Seattle are now taking advantage of this newly passed legislation. You can too.
In December, 2009 Seattle City Council adopted legislation to allow the construction of a DADU eligible lots in single-family zones throughout the city.
Prior to the December 2009 legislation, DADU’s 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 3,200 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.
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.
The cost of permits to build an DADU/AADU varies greatly. The cost of your permits can range from $3,000 to $10,000.
The minimum lot size required for a DADU is 3,200 square feet in neighborhood residential zones. A DADU is limited to 1,000 square feet of gross floor area in neighborhood residential zones, including RSL, and 650 square feet in a lowrise zone. DADU has additional options exempt from the 1,000 limits: a garage and storage areas.
A DADU (Detached Accessory Dwelling Unit) is a separate structure from the main home, typically in the rear of the yard. DADUs are also commonly known as an alley house, backyard studio, or backyard cottage.
An AADU (Attached Accessory Dwelling Unit) is an accessory dwelling unit that is attached to or inside the main home, which is why they are often referred to as a mother-in-law or in-law suite.