Bellingham, WA Accessory Structures: Tiny Homes (2026)

Bellingham regulates tiny homes through the same framework as other residential and accessory structures. A tiny home built on a permanent foundation falls under the 2018 Washington State Building Code (RCW 19.27 + WAC 51-50 + WAC 51-51, which adopts the 2018 IRC including Appendix Q Tiny Houses effective July 1, 2021). Appendix Q allows tiny houses (400 sq ft or less, excluding lofts) to use reduced ceiling heights (6'-8" in habitable rooms, 6'-4" in bathrooms), ladder or alternating-tread-device access to lofts, smaller stair geometry (winders allowed, headroom reduced to 6'-2"), and smaller egress window minimums (5.0 sq ft minimum opening for grade-level egress from sleeping lofts). Site-built or HUD-Code tiny homes on a permanent foundation may be: (1) the primary single-family dwelling — must meet the underlying Bellingham RS zone's minimum lot area, lot width, setbacks, and dimensional standards under BMC 20.30.040 (typically 20-25 ft front yard, 5-7 ft side yard, 20-25 ft rear yard, max 35 ft height; permitted outright when total floor area is under 5,500 sq ft); or (2) an Accessory Dwelling Unit under BMC 20.10.036 — 1,000 sq ft habitable floor cap (1,800 sq ft total including ancillary), 24 ft height, 5 ft side/rear setbacks (zero from alley). WA HB 1337 (RCW 36.70A.680) requires Bellingham to allow at least two ADUs per single-family lot — meaning tiny-house ADUs are explicitly enabled, and Bellingham's BMC 20.10.036 (updated August 22, 2023) already pre-emptively implements this. Cottage developments under BMC 20.28.080 (in the BMC 20.28 Infill Housing chapter, expanded citywide via interim ordinance May 19, 2025) provide another pathway for tiny-house-scale primary dwellings on subdivided lots. Tiny homes on wheels (THOWs) registered as travel trailers, park-model RVs, or recreational vehicles with the WA Department of Licensing are NOT compliant with RCW 19.27 as permanent dwellings and cannot serve as a primary or accessory residence in any Bellingham residential zone — BMC 20.08.020 defines dwelling unit as a structure designed for human occupancy with permanent provisions for living, sleeping, eating, cooking, and sanitation. RV park placement is governed separately by BMC Title 20 and RCW 59.20 (Mobile Home Landlord-Tenant Act). Manufactured (HUD-Code) tiny homes follow WAC 296-150M (WA manufactured home regulation by Labor & Industries) and may be placed in residential zones that permit manufactured homes per BMC 20.10 and applicable neighborhood zoning tables. WA HB 1110 (RCW 36.70A.635) middle-housing rules separately allow duplex/triplex/fourplex configurations under BMC 20.28.110 that can include tiny-house-scale units on single-family lots citywide in Bellingham (~95K population).