ADU 101

Accessory Dwelling Units (ADU's) have become more popular and acceptable in the past few years. The City of Seattle began allowing for ADU's in all residential zones (it had previously been only some south Seattle neighborhoods) in 2009. San Juan County allows for a limited number of permits for ADU's each year.

An ADU can be attached, as in a basement apartment, or detached, as in a backyard cottage, carriage house, or alley flat. The implementation of ADU's can fulfill many goals of sustainable development, including density, affordable housing, and smaller house sizes. As our urban fabric is "re-knit", neighborhoods can become more dense, creating more demand for services, therefore creating more opportunities for walkable neighborhoods and less dependence on a car.

Truly sustainable development also includes social goals, many of which are also met by integrating ADU's: a way for homeowners to have a separate income stream, a mix of income and ages; the ability to stay in one neighborhood through varying phases of life, therefore creating lasting community: kids can live in a backyard cottage as they start on their career path, elderly parents or relatives can live in smaller spaces that require less upkeep and be close to their children and grandchildren. The term "mixed income" may be worrisome, but from a social standpoint, renting out an ADU can more successful than an absentee landlord renting a house, in that owners are close to the rental unit, tenants are close to their landlord, so each keeps an eye on each other. The Kentlands Development in Maryland (designed by New Urbanism pioneers DPZ)  is a neighborhood that has successfully integrated market rate, large suburban housing with backyard rental units. An often cited example is of a woman who lived in her ADU and rented out her large house in order to save money and pay off her mortgage.

Anna spoke to BUILDERnews magazine about the benefits of building an ADU or guest apartment. See the article, including photos of two of our projects that include these structures here.

Hare House in Friday Harbor, Second Floor Plan: an apartment over an office and garage can be used for family, or rented out for extra income.

Summaries of Seattle and King County's rules for Accessory Dwelling Units are below. In the coming weeks we will have summaries of the rules of other cities and counties.

Rules for Seattle ADU

View the Backyard Cottage Overview from the City of Seattle Department of Planning and Development here. 

From the overview:

Among those aware of a backyard cottage in their neighborhood:
• 71% said that the backyard cottage in their neighborhood fit in with the surrounding homes.
• 84% noticed no impacts on parking or traffic directly related to the backyard cottage.
• 83% were supportive or strongly supportive of backyard cottage policy.

Highlights from the Client Assistance Memo 116A, "Establishing an Attached Accessory Dwelling Unit (ADU)."

• Backyard cottages, also known as detached accessory dwelling units (DADUs) are allowed citywide effective Dec. 4, 2009
• Seattle Defines an ADU as: a room or set of rooms in a single family home that has been designed or configured to be used as a separate dwelling unit.
• A single family lot my have one ADU or Backyard Cottage.
• An ADU is limited to an area of 1,000 square feet in the single family structure. A unit in a single-family
  home may exceed the maximum size if the structure was in existence prior to June 1, 1999, and if the
  entire accessory unit is located on the same level.
• A parking space for the ADU is required unless it is located in a designated urban center or village, or if the topography of the site or structure location makes it "unduly burdensome."

Rules for King County ADU's

View a summary from the county with links to the code document (summarized below) here.  

• Accessory dwelling units are allowed in all zones in unincorporated King County except Mineral (M) and Industrial (I), provided that certain conditions are met.
• No separate ADU's are allowed on urban lots less than 5,000 square feet, a non-conforming rural lot, or a lot containing more than one
• Either the primary dwelling or the ADU have to be owner-occupied 
• Only one entrance can be located on the street side