Accessory Structures in Bellingham, WA (2026)
5 verified accessory structures rules for Bellingham, Washington, sourced directly from the municipal code and official government pages.
Verified from official government sources
ADU Rules
Bellingham updated BMC 20.10.036 effective August 22, 2023 to pre-emptively adopt most provisions of WA HB 1337 (RCW 36.70A.680-696) before the state deadline. Up to TWO ADUs are permitted per single-family lot. A detached ADU (D-ADU) may be up to 1,000 sq ft of habitable floor area (1,800 sq ft total including ancillary space for one D-ADU; 2,000 sq ft for two attached D-ADUs). Height limit 24 ft. Setbacks 5 ft side/rear (zero from an alley). No off-street parking required within 0.5 mi of a Whatcom Transportation Authority major transit route. Bellingham was an early ADU adopter (first ordinance 1995).
Bellingham Accessory Dwelling Units (BMC 20.10.036 + WA HB 1337)
Few RestrictionsShed Rules
BMC 20.30.100 governs accessory buildings (including sheds) in Residential Single (RS) areas: max one story or 12 ft height, max 800 sq ft area (larger only by conditional use permit), and located in the rear yard or the rear 22 ft of an interior side yard. The 2018 Washington State Building Code (RCW 19.27) — based on the 2018 IBC/IRC adopted by WAC 51-50 and 51-51 — exempts one-story detached residential accessory structures up to 200 sq ft from a building permit, provided no electrical, plumbing, or mechanical systems are added. Sheds over 200 sq ft, or any shed with utilities, require a Bellingham Permit Center building permit.
Bellingham Shed Rules (BMC 20.30.100 + WSBC)
Few RestrictionsGarage Conversions
Converting a Bellingham garage to habitable space requires a building permit (plus electrical, mechanical, and plumbing permits) from the Bellingham Permit Center under the 2018 Washington State Building Code (RCW 19.27). A garage-to-ADU conversion that adds a kitchen and separate entrance falls under BMC 20.10.036 ADU rules — 1,000 sq ft habitable floor max, 5 ft side/rear setbacks. Per WA HB 1337 (RCW 36.70A.681), Bellingham cannot impose an owner-occupancy mandate and cannot require off-street parking replacement within 0.5 mi of a Whatcom Transportation Authority major transit route.
Bellingham Garage Conversion (BMC 20.10.036 + WSBC)
Some RestrictionsCarport Rules
BMC 20.30.100 treats detached carports as accessory buildings in RS zones: max one story or 12 ft height, max 800 sq ft, located in the rear yard or rear 22 ft of an interior side yard. Attached carports follow the principal-building setbacks (front, side, rear) of the underlying RS or RM zone, with typical 5 ft side and 20-25 ft front setbacks per BMC 20.30.040. Construction requires a building permit from the Bellingham Permit Center under the 2018 Washington State Building Code (RCW 19.27) with engineered anchorage for Bellingham wind loads (~85-95 mph) and Seismic Design Category D2.
Bellingham Carport Rules (BMC 20.30.100 + WSBC)
Few RestrictionsTiny Homes
A tiny home on a permanent foundation in Bellingham is treated either as a primary single-family dwelling (must meet BMC 20.30.040 RS zone standards) or as an Accessory Dwelling Unit under BMC 20.10.036 (1,000 sq ft habitable floor cap, 24 ft height, 5 ft side/rear setbacks). The 2018 Washington State Building Code (RCW 19.27 + WAC 51-51, effective July 1, 2021) adopts IRC Appendix Q (Tiny Houses) — allowing reduced ceiling heights, ladder access to lofts, and small-stair geometry for homes 400 sq ft or less. Tiny homes on wheels (THOWs) registered as RVs cannot serve as a permanent residence in Bellingham residential zones.
Bellingham Tiny Home Rules (BMC 20.10.036 + IRC Appendix Q)
Some RestrictionsLooking for Whatcom County county-wide rules?
County ordinances apply to unincorporated areas and may supplement Bellingham city rules.
Accessory Structures in Whatcom County →