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All ADU Regulations

Newcastle ADU Regulations

Newcastle is a perfect place to build an ADU. Here are Newcastle's up-to-date ADU rules.
Updated Jul 21, 2023


Nestled between Lake Washington and Cougar Mountain, Newcastle is a lively place that offers beautiful scenery and waterfront views. The city's beginnings as a coal mining town helped fuel the growth of the entire Puget Sound region. Newcastle’s peaceful community is an ideal place to live in!


Accessory Dwelling Unit (ADU) projects must comply with all zoning code provisions for single-family residences, including height and setbacks, and the accessory dwelling unit shall be included as part of the impervious surface and floor area limitations for a building site. Zoning maps can be found on the city’s website.

Number of units

One ADU is allowed per single-family dwelling. It can be attached or detached.

Building size

The minimum size of an ADU must be 300 square feet and not more than 1,000 square feet in size. It is not allowed to exceed 40% of the total square footage of the primary dwelling unit and the accessory dwelling unit, excluding the garage.


The ADU will comply with the setback requirements of its zoning code.


There must be at least three parking spaces provided for each primary dwelling unit with an ADU.


Either the principal dwelling unit or the accessory dwelling unit must be occupied by an owner of the property, or an immediate family member of the property owner.
Cottage is here to help you navigate the ADU 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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