Accessory Dwelling Units

Guide to Developing Accessory Dwelling Units

An Accessory Dwelling Unit (ADU), also known by other terms such as a laneway house, granny flat, or mother in law unit, is a separate housing unit on the same lot as a typical single family house. It can be either attached or detached from the main house. It could be rented out to a tenant, or it could be provided for free to the homeowner’s friends or family. 

ADUs are self-contained dwellings. That means an ADU should provide space for cooking, sleeping, and using the bathroom. 

ADUs have a long history in Bremerton. They were a popular form of housing since the days of World War 2, when Bremerton’s population boomed and housing was desperately needed. However, because many of those historical ADUs were small and built cheaply and quickly, they were not often considered in a positive light. Most people can imagine the benefit of having an ADU on their property, whether for housing their loved ones who can no longer live independently, or gaining additional income from rent. However, in recent decades the Zoning Code limited ADU construction, and many property owners that wanted to accommodate an ADU on their property were blocked from doing so. 

The City of Bremerton has recently made changes to the Zoning Code in an effort to make it easier than ever to establish ADUs (Ordinance No. 5410; Ordinance No. 5416). This page will help you to determine whether ADUs are feasible for your property, and inform you of the City’s requirements for ADUs. Below is a table showing some quick standards for ADU construction. Click here for a helpful guidebook that will walk you through developing an ADU. If you have any questions about Zoning Code, Building Code, or Fire Code standards for ADUs, please contact the Department of Community Development at or 360-473-5275.
What is an ADU?An additional, accessory dwelling unit on a lot with an existing principal unit added to or created for use as a complete, independent or semi-independent living unit with provisions for cooking, eating, sanitation and sleeping.
What areas of the City are ADUs permitted?An ADU may be permitted anywhere a new or existing single-family dwelling unit is allowed. ADUs are exempt from the density requirements of the underlying zone.
What is the maximum size of an ADU (square footage)?An ADU is limited to one thousand (1,000) square feet or not more than sixty (60) percent of the principal unit’s total habitable floor area, whichever is greater.

  • If the primary residence is greater than 1667 square feet, an ADU can be 60% of its size.
  • If the primary residence is 1667 square feet or less, an ADU can be up to 1000 square feet.
How many ADUs can a property have? Each property can have a one (1) single family home and two (2) ADUs, for a maximum total of three (3) dwelling units. These ADUs can be either detached or attached to the single family home.
Must the owner live on site?No, owner occupancy is not required.
Is parking required for an ADU?The first ADU is not required to provide an additional off-street parking space. The site must comply with Chapter 20.48 BMC - that means the two (2) paved parking spaces for the single family home must be provided. A 2nd ADU must provide an additional paved parking space, for a total of three (3) spaces.
What are the required yards (setbacks & development coverage)?In the R-10 zone, the minimum front and rear yard setbacks are 15 feet, and the side yard setbacks are 5 feet. Contact a Planner to determine your zone.

An ADU must comply with the development standards of the underlying zone for the principal unit including setbacks, height, and lot coverage. However:

  • An ADU can be placed directly on the rear property line, if it abuts an alley.
  • An ADU can be as close as 3 feet from the side property lines, as long as the wall closest to the property line is built according to fire separation standards.
What are the design standards for ADUs?ADUs must preserve the appearance of the main house as a single-family dwelling,and the design of an ADU should blend into the existing house or the neighborhood. That means no duplex-like designs, and nothing that sticks out like a sore thumb. Try to design an ADU so that the materials used complement the design of the main house.