Accessory Dwelling Units (ADUs)

The 1995 Accessory Dwelling Unit (ADU) ordinance requires review of the existing regulations upon issuance of the 200th ADU permit or before any specific neighborhood exceeds 20 ADUs, which is true of our South Hill Neighborhood. This update intends to analyze the current regulations for attached and detached ADUs, and to recommend possible changes that will ensure implementation of the comprehensive plan, efficient use of land and clear and consistent review processes. Click here to follow the legislative process for the ADU Ordinance update. 

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?

In single family zones, Bellingham only allows ADUs that are within or attached to the main residence. Attached and detached ADUs are allowed in other zones that allow residential uses. 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.

See the ADU Ordinance Update Public Process webpage for a list of past and upcoming meetings, and opportunities to provide public comment.