Accessory Dwelling Units (ADUs)

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On August 7, 2023, the City of Bellingham amended its zoning and process codes to improve ADU standards, permitting process, and consistency with State legislation (see Ordinance 2023-08-022). ADUs are seen as a valuable component in achieving the City’s infill housing goals. There are many benefits to enabling ADU development in Bellingham including increasing housing choice and affordability as well as providing an opportunity for homeowners to earn additional income, age in place, or care for an ailing relative.

An ADU is a separate, self-contained residential unit located on the same lot as an existing single-family home. An ADU has all the basic facilities needed for day-to-day living independent of the main home, such as a kitchen, sleeping area and a bathroom. They are sometimes called “mother-in-law apartments” or “granny flats” because they are often used to house extended family.

An ADU may be created as:

  • In a separate structure on the lot (such as a converted garage).
  • A separate unit within an existing home (such as in an attic or basement),
  • An addition to the home (such as a separate apartment unit with a separate entrance), or
  • In a separate structure on the lot (such as a converted garage).

The permitting process for ADUs varies depending on the scope of work as detailed in Bellingham Municipal Code (BMC) 21.10 and summarized below:

Type I

The Type I permit process is streamlined and used when a proposal meets all applicable ADU standards. A Type I ADU application is a staff level (administrative) review and may be submitted with a building permit application. Notification of surrounding property owners is not required.

Type II

The Type II permit process is used when applicants request minor modifications to ADU development standards. These may be approved by the Planning Director if the criteria in BMC 20.10.036(B)(3) are met.

The Type II Permitting process:

  1. The applicant must submit an ADU permit application along with a mailing list of all owners of property within 500 feet.
  2. Planning staff sends notice of the ADU application to the mailing list and applicable neighborhood representatives.
  3. A decision is made based on the information contained in the application and the written public comments received as a result of the public notice. Comments submitted should be focused on the specific minor modification(s) being requested and how it relates to the applicable evaluation criteria. The decision may be appealed to the Hearing Examiner.

Type III-A

Type III-A Conditional Use Permit (CUP) process is additionally required per BMC 20.10.036(B)(6)(c) if an applicant proposes to build a new detached accessory building exceeding 1,000 SF that includes a D-ADU. An example would be new detached accessory building that includes a 450 SF 2-car garage and 950 SF D-ADU for a total building size of 1,400 SF. Regardless, though the gross square footage of the accessory building may exceed 1,000 SF if the CUP criteria are met, the ADU standards limit the D-ADU within to no more than 1,000 SF.

The Type III-A Process:

  1. The applicant must first hold a pre-application neighborhood meeting.  
  2. The applicant submits ADU and CUP applications along with a mailing list of all owners of property within 500 feet.  
  3. Planning staff sends notice of the applications to the mailing list and applicable neighborhood representatives.
  4. A public hearing is held, during which the Hearing Examiner evaluates the proposal against the criteria listed in BMC 20.16.010 and any public comments received.  
  5. The Hearing Examiner then issues a decision on the proposal. The decision may be appealed to Superior Court.

In what areas of the City are ADUs permitted?Attached and detached ADUs are allowed in most areas that allow residential development, including single-family zoned areas. ADUs are exempt from the density requirements of the underlying zone. ADUs are not permitted in the Lake Whatcom Watershed that drains to Basin One (BMC 16.80.040).
How many ADUs can a property have? Eligible properties can have one single family home and two ADUs, for a maximum total of three dwelling units. ADUs can be in any configuration of attached or detached units.
What is the maximum size of an ADU?An ADU is limited to 1,000 square feet.
What is the height limit for ADUs?Attached ADUs must comply with the height limit of the housing type with which it is being built. Detached ADUs shall be no higher than 24 feet under BMC 20.08.020, height definition No. 1 or 12 feet under height definition No. 2
Must the owner live on site?Owner occupancy is only required in areas zoned residential single until occupancy requirements are preempted by the State law (approximately January 1, 2026).
May the ADUs be sold separately from the primary dwelling unit?Yes, the primary dwelling and ADU(s) may be sold separately. An example of this is condos. Note that the property cannot be subdivided for separate “fee-simple” ownership, which means a single entity owns the land. The City is not directly involved in the formation of a condominium, which is governed by state law (RCW 64.34 or 64.90) and administered locally at the county level.   Note: In areas zoned “residential single,” the owner of at least one unit must reside on site.
Is parking required for an ADU?Generally, one on-site parking stall is required for an ADU. However, no parking is required when either improved public street parking is available on at least one side of the block face whereon the ADU is proposed, or the ADU is within one-half mile walking distance to a “major transit route.” Most Whatcom Transportation Authority GoLines qualify; specific routes should be verified with City staff.
How does a pre-existing unit become legal?Homeowners with existing non-permitted ADUs must apply to make them legal. Units that are not legalized will be subject to enforcement. Pre-existing units must meet the same requirements as new ADUs, including parking and building code standards.   Note: Not all two or more-unit structures in single family zones are illegal. Such units may have been built under an old zoning code that allowed such development. If this is the case, the unit may be a legal nonconforming use. Applications to establish a legal non-conforming use are available at the Permit Center

Watch to learn all about ADUs in Bellingham

This panel discussion provides a comprehensive overview of ADUs in Bellingham, covering key aspects of financing, permitting, construction, rental, and sale.

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Contact Us

For questions or more information, please contact the Planning and Community Development Department at planning@cob.org or 360-778-8300.

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