5 county-level rules, plus city-specific rules for 1 city in Whatcom County, Washington.
Verified from official government sources
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.
A one-story detached shed of 200 square feet or less needs no building permit in Whatcom County, but it must still meet zoning setbacks, separation from other buildings, and fire and natural-resource rules.
Whatcom County, WA — Accessory Structures
An accessory structure is a structure that is customarily accessory to and incidental to the dwelling or primary use located on the same lot.
Converting a garage into living space in Whatcom County requires a building permit and must meet habitable-room code for egress, ceiling height, insulation, and ventilation. If it becomes a separate unit, ADU standards under WCC 20.80.910 apply.
A carport is an accessory structure in Whatcom County. One that exceeds the 200-square-foot exemption needs a building permit, must meet zoning setbacks, and counts toward the lot coverage limits for your zone.
In Whatcom County, a tiny home on a permanent foundation is a dwelling under the building code and can qualify as an ADU under WCC 20.80.910. A tiny home on wheels is treated as an RV, not a permanent residence on a standard lot.
1 cities in Whatcom County have their own accessory structures rules. Each link goes to that city's dedicated page with code citations.
See every category we cover for Whatcom County — parking, noise, fences, fires, animals, pools, and more.
Whatcom County Ordinance Hub →