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Bellingham, WA Accessory Structures: ADU Rules (2026)

Some Restrictions

Compiled from the official code textEditor Martyn O'NeillLast verified August 2026

ADU rules in Bellingham, WA, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.

Key Facts

ADUs per lot: Up to two, attached or detached
Max ADU size: 1,000 sq ft per unit
D-ADU + ancillary cap: 1,800 sq ft (2,000 for two)
D-ADU setback: 5 ft side/rear; none on alley
D-ADU height: 24 ft (or 12 ft, alt. definition)

ADU Eligibility Quick-Check

An Accessory Dwelling Unit (ADU) is a smaller, independent living unit on the same lot as a single-family home: converted garages, detached cottages, basement or attic conversions, and attached additions all qualify. Most states have streamlined ADU permitting since 2020, but local rules still control size, height, and setback.

Is your lot zoned single-family or multi-family residential?
Does your lot have at least 1,200 sq ft of buildable space?
Is your existing home owner-occupied (in most states this is not required, but some require it for ADU permits)?
Will the ADU stay under your state's size cap (commonly 850-1,200 sq ft for detached)?
Can you provide one off-street parking space (waived in many states within 0.5 mi of transit)?

If you answered 'yes' to most of these, you likely qualify in Washington under recent ADU streamlining laws. The Bellingham, WA rules below cover local size, height, and setback requirements.

Summary

Bellingham allows up to two accessory dwelling units per lot, capping each ADU at 1,000 square feet and detached units at 24 feet tall under Bellingham Municipal Code § 20.10.036.

5. a. 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. 6. a. An ADU shall not exceed 1,000 square feet. 7. b. A five-foot side and rear yard setback shall be provided... 8. A D-ADU shall be no higher than 24 feet under BMC 20.08.020, height definition No. 1 or 12 feet under height definition No. 2.

View official code

Official source re-checked September 8, 2026: no newer edition of the code had been published (publisher’s edition: current through Ordinance 2026-06-015, passed June 1, 2026).

Full Breakdown

BMC 20.10.036 lets a lot have up to two ADUs, attached or detached, each capped at 1,000 square feet; a detached ADU (D-ADU) can add up to 800 square feet of attached garage, workshop or shed space, but the whole structure tops out at 1,800 square feet (2,000 for two attached D-ADUs) without a conditional use permit. D-ADUs must keep a five-foot side/rear setback (none along an alley) and stay under 24 feet under Bellingham's first height definition, or 12 feet under its second. ADUs otherwise follow the principal unit's zoning for height, setbacks, floor area, parking and open space.

Violations & Fines

Building a third ADU on a lot, exceeding the 1,000-square-foot per-unit cap, or a D-ADU exceeding 1,800 (or 2,000) square feet without a conditional use permit violates BMC 20.10.036 and can block permit approval or occupancy.

Frequently Asked Questions

How many ADUs can I build on one lot in Bellingham?

Up to two, in any mix of attached or detached units, under BMC 20.10.036(B)(5)(a): each still capped at 1,000 square feet.

Does Bellingham require the owner to live on-site for an ADU?

No. Bellingham's ADU code sets no owner-occupancy requirement: state law (HB 1337) bars most such mandates, and the local rules focus on size, setback and height limits instead.

Sources & Official References

[1]Bellingham Municipal Code § 20.10.036

Other rules in Bellingham

Parking Rules: Street Parking LimitsSome Restrictions Noise Ordinances: Construction HoursSome Restrictions Shed & Carport RulesSome Restrictions ADU Impact FeesLight Restrictions Garage ConversionsSome Restrictions ADU Rental RestrictionsSignificant Restrictions ADU Owner OccupancyFew Restrictions Tiny HomesSome Restrictions Noise Ordinances: Barking DogsSome Restrictions Parking Rules: Commercial & Oversized VehiclesSome Restrictions Parking Rules: EV ChargingSome Restrictions Animal Ordinances: Mandatory Spay/NeuterSome Restrictions

All Bellingham rules

How Bellingham compares: Easiest Cities to Build an ADU·Compare Bellingham to another location·View the Washington accessory structures overview

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