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The Complete Guide to ADU Ordinances in King & Snohomish Counties

attached garage studio adu 1

ADU (short for accessory dwelling unit) requirements vary by municipality. In Western Washington, most cities allow both attached (AADU) and detached (DADU) units. That said, no two cities are alike.

To help you understand what you can build in your neighborhood, we’ve compiled the core rules that apply to ADUs in Seattle and its surrounding cities. All information listed here is courtesy of The Master Builder’s Association of King & Snohomish County and is current as of January 2020. 

Remember that this list is just a starting point. Click the link on each city’s name to read more about its ADU codes, or give us a call. We can review the specifics and discuss what’s possible. 

Arlington

Everett

Federal Way

Issaquah

Kenmore (in the process of updating code)

Kent

Kirkland (in the process of updating code)

Lake Stevens

Lynnwood

Marysville

Mercer Island

Mill Creek

Mukilteo

Newcastle

North Bend

Renton

Renton (in the process of updating code)

Sammamish

SeaTac

Seattle 

Shoreline

Snohomish

Snoqualmie (in the process of updating code)

Stanwood

Tukwila

Unincorporated King County

Unincorporated Snohomish County

Woodinville