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All ADU Regulations

Bellevue, Washington

Bellevue is a perfect place to build an ADU. Here are up-to-date ADU rules for Bellevue.
Updated May 21, 2023


Bellevue, Washington is a thriving city located in King County. Known for its stunning natural scenery, robust economy, and diverse community, Bellevue is a wonderful place to call home. If you're considering building an Accessory Dwelling Unit (ADU) in Bellevue, it's important to familiarize yourself with the city's regulations and guidelines.
ADUs offer an opportunity to increase housing options, promote affordability, and enhance the livability of Bellevue neighborhoods.
As of early 2023, ADUs in Bellevue can take the form of attached structures (AADUs) only.


ADUs in Bellevue must adhere to all local zoning requirements.

Number of units

In Bellevue, one home may have one ADU maximum.

Building size

ADUs in Bellevue must be between 300 square feet and 800 square feet, excluding the garage area. Additionally, the size of the existing home determines the maximum size of a Bellevue ADU: the maximum allowable size for an ADU is 40% of the total area of the main home and the ADU together. Some exceptions may exist.


Accessory structures in Bellevue residential districts can have a maximum height of 15 feet, with some exceptions.


Accessory structures are required to follow the same front and side setbacks that apply to the main home. A five-foot setback at the back of the lot is required for an accessory structure, with some exceptions.


An ADU must have at least one dedicated off-street parking space in addition to any parking designated for the main home.


In Bellevue, the owner of the property must occupy either the ADU or the main home.

Other Considerations

To build an ADU, all Bellevue technical code standards must be adhered to, including building, electrical, fire, and plumbing codes, and more.
Cottage is here to help you navigate the process. Reach out to us and we’ll help you build a custom ADU to fit your unique property characteristics and local regulations!

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