Bellingham’s ADU guidance applies across a range of principal dwelling forms, but the Lake Whatcom watershed is a named geographic exception. Check the City boundary, residential-use permission, and watershed map before counting a lot as eligible.
Confirm the location and principal form
The City’s September 17, 2026 update says attached and detached ADUs are allowed in areas where residential development is allowed, except in the Lake Whatcom watershed. The listed principal forms include single-family homes, duplexes, triplexes, fourplexes, townhomes, and other principal units. This broad form coverage still depends on the parcel’s zoning and mapped location.
The City guide caps the number at two ADUs per lot and each unit at 1,000 square feet. It says owner occupancy and additional ADU parking are not required. These are summarized City standards; the current Bellingham Municipal Code and any project-specific review remain controlling.
Resolve the watershed and project route
Use the City’s current zoning and watershed maps to determine whether the property is inside the Lake Whatcom watershed. If the map or boundary is unclear, ask Planning and Development to confirm it before relying on the ordinary residential-area route. A detached ADU that includes ancillary space and larger residential projects may follow separate review processes, and utilities and site standards still apply.
This page does not establish a parcel result or building approval. For the statewide urban framework and the separate rural county option, compare Seattle’s ADU count screen and Washington’s rural detached ADU route.