Accessory Dwelling Units (ADUs)

The 2018 Accessory Dwelling Unit (ADU) ordinance requires review of the existing regulations By City Council when one of the following occurs:

  1. by December 31, 2025; or
  2. when the city issues 200 D-ADU permits citywide; or
  3. when the city issues 25 D-ADU permits in any one neighborhood as defined in Chapter 20.00 BMC, Zoning Tables.

What is an ADU?

An ADU is a small, self-contained residential unit located on the same lot as an existing single-family home. As the term “accessory” implies, ADUs are defined to be smaller in size and prominence than the main residence on the lot, and aid the City in providing a range of housing choices for residents. They are sometimes called “mother-in-law apartments” or “granny flats” because they are often used to house extended family. An ADU has all of the basic facilities needed for day-to-day living independent of the main home, such as a kitchen, sleeping area and a bathroom. An ADU may be created as a separate unit within an existing home (such as in an attic or basement), and addition to the home (such as a separate apartment unit with separate entrance), or in a separate structure on the lot (such as a converted garage).

What are the local restrictions?

Attached and detached ADUs are allowed in most areas that allow residential development, including single family zoned areas. Whether attached or detached from the main residence, the City of Bellingham requires that the main residence and the ADU are owned by the same person, and the owner must live on site. Below are some local resources that can provide more details:

Other Resources

Staff Contact: Chris Koch at or 360-778-8349.



Planning & Community Development