Considering an Accessory Dwelling Unit in Whatcom County?

July 11th, 2018 - Catherine A. Moore

Accessory dwelling units (or ADUs for short) are currently a topic of much discussion and many new laws in Whatcom County. An ADU is an attached or detached dwelling unit sharing a property with a single-family home. Examples of ADUs include mother-in-law suites, backyard cottages, garden suites, granny flats, garage apartments, and laneway houses. ADUs provide homeowners extra income, give renters more rental options, and help alleviate some pressure on cities to sprawl. They are also cause for concern among those who are wary of increased congestion in their neighborhoods.

This post provides a brief overview of some of the kinds of ADU regulations you might see in Whatcom County. If you’re considering building an ADU, renting out an ADU, or concerned about a neighbor’s ADU, read this blog for background, then call or visit your city or county’s permit office.

Zoning Restrictions

The zone in which your property is located will dictate whether you can have an ADU and might also impose additional restrictions on the kind of ADU you may have. Check with your permit office to determine which zone you’re in; do not assume you can tell which zone you live in based on the property uses you see around you.

ADU-Specific Permits

Some jurisdictions require a property owner seeking to establish and ADU to get approval first. For example, in several of Whatcom County’s zones, ADUs are only allowed with the approval of the County after the property owner has submitted an ADU application providing proof of a number of considerations. See Whatcom County Code 20.32.132. In Ferndale, property owners go through a similar process. See Ferndale Municipal Code 18.34.070. However, in other jurisdictions, it may only be necessary to submit a building permit.

Owner-Occupancy Requirements

Generally, the owner of the property must live in either the primary residence or the ADU. Whatcom County requires a deed restriction be recorded mandating that one of the units be owner-occupied. Bellingham and Ferndale require a deed restriction and require owners to submit an affidavit every other year affirming that one of the two units is owner-occupied in residential zones. Bellingham Municipal Code 20.10.035(B); Ferndale Municipal Code 18.34.020(O).

Size Restrictions

You are likely to face restrictions on the total size of your ADU. For example, in Lynden’s residential single-family zone, ADUs must not exceed 600 square feet or 40% of the square footage of the primary residence, whichever is smaller, and they may contain only one bedroom. See Lynden Municipal Code 19.16.030(G). Bellingham’s single-family residential zone limits ADUs to 800 square feet, and 40% or 50% of the size of the main residence depending on the circumstances. See Bellingham Muncipal Code 20.10.035(B).

Attached-Detached restrictions

Many zones require that ADUs be attached to the main dwelling. For example, in Lynden’s single family residential zone, ADUs must be attached to the main home. Lynden Muncipal Code 19.15.030. The same is true in Bellingham’s single-family residential zone. Bellingham Muncipal Code 20.10.035(B); 20.30.030(A).


Are you in a community with an HOA? If so, you might be subject to additional restrictions. Be sure to read your CC&Rs carefully to determine whether they place additional limitations on your ability to build or rent an ADU. Your permit office might not be able to tell you if you are subject to CC&Rs, so it is important that you fully understand your CC&Rs yourself.

As ADUs are a hot topic in land use law right now, the laws cited above might change. Again, please visit your permit office before taking any action to establish an ADU. You can find your permit office by visiting your city or county’s website, but for the convenience of most folks in Whatcom County, here are links to the permit offices for Whatcom County, the City of Bellingham, the City of Lynden, and the City of Ferndale. If you have additional questions or concerns the permit office is unable to address, a local land use attorney would likely be able to help you. Finally, if you’re considering building an ADU to rent, you might find our blogs on landlord tenant law helpful.

Disclaimer: This article and blog are intended to inform the reader of general legal principles applicable to the subject area. They are not intended to provide legal advice regarding specific problems or circumstances. Readers should consult with competent counsel with regard to specific situations.

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