Bellingham, WA Accessory Structures: Garage Conversions (2026)

A Bellingham garage-to-living-space conversion is a change-of-occupancy under the 2018 Washington State Building Code (RCW 19.27 + WAC 51-50) — moving from IRC Group U (utility) to IRC Group R-3 (residential). The Bellingham Permit Center (210 Lottie Street, 360-778-8300) issues building, electrical, mechanical, and plumbing permits as required. Code minimums for the converted space include: 7 ft minimum ceiling height (IRC R305), light and ventilation per IRC R303 (8 percent natural glazing of floor area, with operable window area for ventilation), egress windows from each sleeping room per IRC R310 (5.7 sq ft net openable, 24 in minimum opening height, 20 in minimum opening width, 44 in maximum sill height), smoke alarms in each sleeping room, hallway, and on each level per IRC R314, CO alarms outside each sleeping area per IRC R315, separation of attached private garages from the dwelling unit per IRC R302.6 (no longer required after the garage is fully converted), 2021 Washington State Energy Code (RCW 19.27A) insulation and air-sealing requirements (notably higher than national IECC due to WA climate amendments), and structural confirmation that the existing garage slab and walls meet R-3 occupancy loads. If the conversion adds cooking facilities (kitchen with sink, range, refrigerator) and a separate exterior entrance, the converted garage becomes an Accessory Dwelling Unit (ADU) under BMC 20.10.036 — subject to the 1,000 sq ft habitable floor cap (1,800 sq ft total including ancillary space), 24 ft height limit, and 5 ft side/rear setbacks (zero from alley). Under WA HB 1337 (RCW 36.70A.681), Bellingham cannot require owner-occupancy as a condition of ADU approval, and cannot impose an off-street parking replacement requirement within 0.5 mi of a Whatcom Transportation Authority major transit route (high-frequency route at 15-minute intervals for at least 5 peak hours weekdays). Most Bellingham residential properties fall within this transit buffer due to WTA's network. Outside the buffer, Bellingham may require replacement parking under BMC Chapter 20.12 if the garage conversion eliminates the dwelling's required off-street parking. The Bellingham ADU Homeowner Handbook walks owners through the conversion process. Compliance review is by the Bellingham Permit Center and Planning & Community Development Department. Permit fees per BMC 14.32.020 fee schedule, typically $1,500-$3,500 depending on scope.