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An accessory dwelling unit, also known as an ADU, is a secondary residential living space on the same lot as a single-family home. It can be attached to the primary residence or it can be completely detached, referred to as a DADU in some areas.
To be considered an ADU, the unit must:
- Be on the same lot as the principal residence.
- Include living, sleeping, kitchen, and bathroom facilities.
- Have a private lockable entrance door.
ADU Statistics in 2023
In 2023, homes with ADUs made up 2.3% of the total residential properties sold by NWMLS brokers. The vast majority of homes with ADUs that sold in 2023 were in King County (462 listings), however, a good number of homes with ADUs were also sold in Pierce (167), Snohomish (150), Kitsap (78), Thurston (60), Island (51) and Whatcom (54), with a little over 300 scattered throughout other counties covered by Northwest MLS.
Homes with ADUs typically attract a specific type of buyer. NWMLS data shows that on average, homes with ADUs were on the market longer than homes without ADUs in most counties.
However, patience may pay off when it comes to listing a home with an ADU. In 2023, the median sold price for a home with an ADU was higher when compared to homes without an ADU.
Accessory dwelling units are a great way to provide more living space for family, earn extra cash, or add significant value to your home. If you are interested in purchasing a home with an attached or detached accessory dwelling unit, NWMLS brokers are here to help! Equipped with advanced search options to help you find homes in your ideal location, they are also able to search for ADU square footage and number of bedrooms and bathrooms, to ensure you find exactly what you are looking for.
Additional Resources:
Olympia considering changes to ADU regulations to help ease housing crunch
Renton’s Permit Ready ADUs drawing praise
ADUs gaining acceptance as one approach to ease housing shortages
Architect, ADU advocate outlines ways to boost stock of affordable housing
Bellingham considers adding more ADUs to ease housing crunch
Please note: ADUs are not legal unless they have been established through a permit process. A legally permitted unit in the home is called an attached accessory dwelling unit (AADU). A legally permitted unit on the property (but not within the home) is called a detached accessory dwelling unit (DADU) or backyard cottage. Tiny houses, with foundations, are considered DADUs.