Bellingham ADU rules
✓ Verified against code · August 20, 2026
Current rules under BMC 20.10.036 (Accessory Dwelling Units), adopted by Ordinance 2025-12-035 §2, in effect since December 23, 2025. Bellingham completed its HB 1337 alignment in Ordinance 2025-12-035, effective December 23, 2025 — roughly six months after the state's June 30 deadline. Two of the standards below rest on interim ordinances rather than permanent code: the citywide elimination of parking minimums, and the companion infill regulations that sunset in December 2026.
Common questions, answered from the code
How many ADUs can I build in Bellingham?
Two per lot, in any combination you like. The code is explicit that no more than two are permitted alongside the principal unit and that they may be in any configuration of attached or detached units — so two detached ADUs on one lot is allowed, as is one of each.
BMC 20.10.036(F) · Permalink
How tall can a detached Bellingham ADU be?
Either 24 ft or 12 ft, depending on which of the city's two height definitions you measure by. The first measures from the lowest existing grade at the wall and allows 24 ft; the second measures from the highest existing grade within 20 ft of the building and allows 12 ft. Where both are genuinely available to your site, you elect which to use, subject to the director agreeing the choice won't be unduly detrimental to neighbouring properties. On a sloping lot that election is the single most consequential decision in the design.
BMC 20.10.036(B)(6)(c); BMC 20.10.070 · Permalink
Can I Airbnb my Bellingham ADU?
It depends on whether it is attached. An attached ADU may be short-term rented anywhere in the city. A detached ADU may only be short-term rented in commercial, multi-residential and urban-village zones — or in a single-family zone once the citywide rental vacancy rate reaches 4%. Either way, only one of the main house or the ADU may hold a short-term rental permit, never both.
BMC 20.10.037 · Permalink
Can I sit a Bellingham ADU on the alley line?
Yes. Bellingham requires 5 ft to the side and rear generally, but imposes no side or rear setback at all where the lot abuts a public alley. A detached ADU may also occupy the rear yard and the rear 22 ft of an interior side yard.
BMC 20.10.036 · Permalink
Can I sell a Bellingham ADU separately?
Yes, and there are two routes with different consequences. An ADU may be condominiumized and sold separately from the main house. Subdividing a detached ADU onto its own lot is also possible, but that path triggers an affordable-housing deed restriction under BMC 20.29 — so confirm which mechanism you are using before you assume the unit is freely saleable.
BMC 20.10.036; BMC 20.29 · Permalink
The rules at a glance
| ADUs allowed per lot | Two per lot. The code says it directly: "No more than two ADUs shall be permitted in conjunction with the principal unit on a single lot of record. The ADUs may be in any configuration of attached or detached units."BMC 20.10.036(F) |
| Maximum size | 1,000 sq ft per ADU. Up to 800 sq ft of ancillary non-living space — a garage, workshop or shed — may be attached to a detached ADU without counting against that cap, though the ADU and its ancillary space together are limited to 1,800 sq ft with one detached ADU or 2,000 sq ft with two, absent hearing examiner approval.BMC 20.10.036 |
| Detached ADU height | 24 ft measured under the city's first height definition (from the lowest existing grade at the wall), or 12 ft measured under the second (from the highest existing grade within 20 ft of the building). Where both are available the owner elects which to use, subject to the director finding the choice is not unduly detrimental to neighbouring properties.BMC 20.10.036(B)(6)(c); BMC 20.08.020; BMC 20.10.070 |
| Detached ADU setbacks | 5 ft to the side and rear, measured to the foundation — and no side or rear setback at all where the lot abuts a public alley. A detached ADU may sit in the rear yard and in the rear 22 ft of an interior side yard.BMC 20.10.036 |
| Off-street parking | None required. The ADU chapter sets only a minimum stall size if parking is provided voluntarily, and citywide minimums were eliminated separately.BMC 20.10.036; BMC 20.12.010; Ord 2025-11-030 (interim) |
| Owner-occupancy | Not required. The city puts it plainly: owners used to have to live on site as a condition of adding an ADU, and no longer do.BMC 20.10.036 (absence verified); City ADU page |
| Lot coverage / floor area | No ADU-specific cap. The ADU and principal unit together must meet the base zone's height, setback, floor-area and FAR standards for the site.BMC 20.10.036 |
| Permit path & timeline | Type I director review for the large majority of conforming ADUs; Type II if the ADU brings the lot to seven or more dwelling units; Type III-A, with a pre-application neighbourhood meeting and a public hearing, otherwise. No published review timeline.BMC 20.10.036; BMC Ch. 21.10 |
Worth knowing
- One pre-approved ADU plan is registered with the city — a 1,000 sq ft, two-bedroom design — offering a faster and cheaper permit path.
- Short-term rentals are split by ADU type: attached ADUs may be rented short-term citywide, detached ADUs only in commercial, multi-residential and urban-village zones, or in single-family zones once the citywide vacancy rate reaches 4%. Only one of the principal unit or the ADU may hold a short-term rental permit, never both (BMC 20.10.037).
- ADUs may be condominiumized and sold separately from the main house.
- Subdividing a detached ADU onto its own lot triggers an affordable-housing deed restriction (BMC 20.29).
- An unpermitted ADU built before 1995 can be legalized under the current code.
On our watchlist
The citywide elimination of parking minimums rides on interim Ordinance 2025-11-030. If it lapses without permanent adoption, a baseline parking minimum could return.
Companion interim Ordinance 2025-12-032 (infill and middle-housing regulations) sunsets December 4, 2026 absent further council action, which would change the site-design context ADUs sit within.
Whether an interim measure held HB 1337 compliance between the June 30, 2025 deadline and the December 23, 2025 effective date is unverified.
Primary sources
- BMC 20.10.036 (Accessory Dwelling Units)
- BMC 20.10.070 (height definition election)
- City of Bellingham ADU ordinance updates
Other Washington cities
Auburn · Bellevue · Bothell · Burien · Edmonds · Everett · Federal Way · Issaquah · Kent · Kirkland · Lynnwood · Olympia · Puyallup · Redmond · Renton · Sammamish · Seattle · Shoreline · Spokane · Tacoma · Vancouver
Not legal advice. Every fact above cites the code section it comes from — check the cite, or ask your city’s planning department to confirm your specific lot. Spotted an error or a new ordinance? See about to reach us; corrections are logged in the changelog.