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Understanding Accessory Dwelling Units and Detached Accessory Dwelling Units in Seattle

Published on August 16, 2016 under Building Trends
Understanding Accessory Dwelling Units and Detached Accessory Dwelling Units in Seattle

Mother-in-law apartments and tiny homes provide private space for extended family to live in, or as additional guest dwelling space. They can also offer a homeowner additional methods of income from leasing it in a long term rental or offering short-term vacation rentals with tools like VRBO and AirBNB. However, these dwellings require specific permitting, and you must follow the necessary process to acquire the appropriate permit before constructing or installing this kind of building on your property within the City of Seattle.

How are these buildings classified?
Tiny homes and mother-in-law apartments are classified in the City of Seattle as Accessory Dwelling Units (ADU) or Detached Accessory Dwelling Units (DADU). An ADU or DADU is “a separate living space within a house or on the same property as an existing house,” according to the city.

What is the difference between an ADU and DADU?
An ADU is a legally permitted unit within the home, such as a garage or basement apartment that is equipped with a kitchen separate of the main kitchen. A DADU is a legally permitted unit that is on the same property as the main house, but is detached from it, as the name infers. Detached accessory dwellings are also referred to as backyard cottages. If you have a tiny home with a foundation, it would be classified as a DADU for legal permitting.

What if my tiny home has wheels?
Unfortunately, the City of Seattle classifies tiny houses on wheels as camper/trailer vehicles, and long-term residence in a camper trailer is not permitted within city limits. Wheeled tiny houses must follow the city’s large vehicle parking rules.

Are there any requirements for an ADU or DADU?
The city limits the size and placement of a DADU, and requires that the owner lives either in the house or the additional unit (with a signed owner occupancy covenant). An ADU must be 1,000 square feet or less within a single-family home, or 650 square feet or less if it is within a townhouse or rowhouse. DADUs are limited to 800 square feet in single-family zones and 650 square feet in lowrise zones. In order to build a DADU on your property, the lot must be a minimum of 4,000 square feet within single-family zones. Both ADUs and DADUs must meet the city’s current standards for land use, environmentally critical areas, shoreline, residential, building, electrical, mechanical, and energy codes. Both unit types must also receive a single off-street parking space, except in designated zones.

What kind of permit do I need for my ADU or DADU?
To add an ADU within your existing home or to build a new detached unit (DADU), you need to apply for a permit for construction of an addition/alteration. In order to legalize an existing (nonpermitted) unit, apply for a construction permit to establish use.

The City of Seattle recommends hiring a design professional to help you plan your ADU or DADU, in order to be sure you follow the correct process for permitting and construction — plus, a little expert guidance throughout the design concept process can help you achieve big dreams for your tiny home!

Featured image courtesy of Tammy Strobel

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