ADU rules in Whatcom County, WA — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
Inside urban growth areas, Whatcom County now allows up to two ADUs per lot with no owner-occupancy requirement (WCC 20.80.910). Rural lots outside a UGA still need an administrative use permit and must meet large minimum lot sizes.
Whatcom County regulates ADUs under WCC 20.80.910. Within urban growth areas — excluding the Lake Whatcom Watershed, commercial, Agriculture, Rural, and Rural Forestry zones — an ADU is now a permitted use: up to two per lot, no minimum lot size, no owner-occupancy, and only one off-street space required on lots under 6,000 square feet. This tracks Washington's HB 1337. Outside a UGA, rural zoning controls: a detached ADU typically needs an administrative use permit and a large minimum lot (4.5 acres in Rural Residential up to 40 acres in Agriculture). ADUs generally may not exceed 1,248 square feet.
Building an ADU without the required building permit — or a rural detached ADU without an administrative use permit — is a code violation that must be legalized or removed.
Other ordinances people look up for this city. Green dot = verified primary-source excerpt.
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