Bellingham is one of the most ADU-friendly cities in Washington State. Following the December 8, 2025 ordinance update — which aligned city code with state HB 1337 mandates — most residential lots within city limits can now support up to two ADUs with streamlined Type I permitting.
This guide covers Bellingham's specific ADU rules under BMC 20.10.036, the permit process, costs unique to the city, and a neighborhood-by-neighborhood breakdown of opportunities and restrictions.
What's Allowed in Bellingham
Max ADUs per lot
2 (any configuration)
Max ADU size
1,000 sq ft (CUP for larger)
Max height
24 feet
Permit type
Type I (streamlined)
Permit timeline
4–6 weeks
Owner occupancy
No longer required (HB 1337)
Impact fees
Currently none for ADUs
Condo ownership
Allowed
Bellingham ADU Zoning Rules (BMC 20.10.036)
Where ADUs Are Allowed
ADUs are permitted in most residential zones within Bellingham city limits — anywhere listed as a permitted use. The major exception is the Lake Whatcom Watershed (Chapter 16.80 BMC), where ADUs are banned to protect drinking water quality. For the complete code breakdown, see our BMC 20.10.036 guide.
Source: BMC 20.10.036(B)(1)
Size Limits
- General maximum: 1,000 sq ft
- D-ADU floor area includes all attached ancillary space (garage, workshop, shed)
- Basement exception: A-ADU conversions are exempt from the size limit if the primary home has been on the property 5+ years
- D-ADU may exceed 1,000 sq ft only with a Conditional Use Permit approved by the Hearing Examiner
Source: BMC 20.10.036(B)(6)
Setbacks
ADUs must comply with all standard zoning setbacks for the primary dwelling. However, there's an important exception:
A detached ADU may be placed less than 5 feet from the property line if:
- 1. A joint agreement with the adjoining property owner is recorded, OR
- 2. The planning director determines impacts are negligible (considering slope, existing development, etc.)
Source: BMC 20.10.036(B)
Permit Types
Type I (Most ADUs)
Administrative review. May be submitted with building permit. No neighbor notification required. This is the fastest path — typically 4\u20136 weeks.
Type II
Required for 7+ dwelling units (including ADUs) per Interim Middle Housing Ordinance 2025-12-032. Requires 500-foot mailing list notice.
Conditional Use Permit (CUP)
Required for oversized D-ADUs exceeding 1,000 sq ft. Public hearing before the Hearing Examiner with 500-foot notice to neighbors.
Source: BMC 21.10.040, BMC 20.10.036
Lake Whatcom Watershed: ADUs Prohibited
If your property falls within the Lake Whatcom Watershed boundary, ADU construction is currently prohibited under Chapter 16.80 BMC. This includes neighborhoods like Silver Beach and parts of Sudden Valley. Our feasibility study checks this automatically.
Read the full Lake Whatcom Watershed guideKnow your property qualifies? See the full Bellingham ADU cost breakdown or let our permit specialist handle the paperwork — $1,500 deposit, applied to your project cost. Not sure yet? Get a free feasibility study.
Bellingham Neighborhoods for ADUs
ADU feasibility varies significantly by neighborhood. Our ADU design team tailors plans to each neighborhood's unique lot characteristics. Here are the key highlights:
Birchwood
Some of Bellingham's largest residential lots (up to 1 acre). Multi-ADU development potential with deep rear lots. Transit parking exemptions available.
Sunnyland
The most ADU permits of any Bellingham neighborhood. Dense, walkable, transit-adjacent. Smaller lots mean tighter setbacks — consider attached ADU or basement conversion.
Columbia
Established neighborhood with proven ADU track record. Good mix of lot sizes and configurations.
Cordata
Transit-adjacent with parking exemptions. Growing neighborhood with newer infrastructure. Strong rental market.
Fairhaven
Historic district considerations may affect design review. Walkable location with strong rental demand near WWU and downtown.
Silver Beach
Lake Whatcom Watershed — ADUs NOT allowed. Beautiful lakefront but strict environmental protections override ADU permissions.
Related Guides
Last updated: March 2026. This guide references BMC 20.10.036 as amended December 8, 2025. Not legal advice.
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