ADU Rulebook

City · Washington

ADU rules in Bellevue

5 sources

These are the primary sources for accessory dwelling unit regulations in Bellevue: the city's own zoning code, planning department pages, and permit guides. Start here before talking to anyone: the rules below are what your permit reviewer will apply.

Rules at a glance

Detached (backyard) ADU
Allowed

Up to two ADUs (attached or detached) per lot in any land use district that allows a single-family dwelling. Detached ADU standards were added with the 2025 middle housing/ADU update (Ord. 6851, 6-24-25); the 2023 reform covered attached ADUs only. Detached ADUs limited to 24 ft height (28 ft as an addition over an existing accessory structure) and follow middle housing dimensional standards per LUC 20.20.538, except they may be sited at an alley lot line.

LUC 20.20.120.C.1, 20.20.120.E
Attached or internal ADU
Allowed

Attached ADUs must be located within or attached to the primary structure and are subject to the same height and setback requirements as the primary structure. Attached ADU floor area does not count toward the maximum allowable square footage for single-family and middle housing projects under LUC 20.20.390.

LUC 20.20.120.C.1, 20.20.120.D
Maximum size
1,200 sq ft (attached and detached); Director may approve more for an ADU on a single floor of the primary structure or for additions to/conversions of existing detached accessory structures; guest cottage conversions exempt; up to 300 sq ft of parking or unheated storage per ADU excluded from the cap

Cap raised from 800 to 1,200 sq ft by Ord. 6746 (2023).

LUC 20.20.120.C.3
Owner occupancy
Not required

Current LUC 20.20.120 contains no owner occupancy requirement. The city's ADU Reform LUCA page confirms Ord. 6746 (adopted 7-17-23) eliminated it: property owners are no longer required to reside on the same site as the ADU. Consistent with WA HB 1337 (RCW 36.70A.680).

LUC 20.20.120 (no owner occupancy provision); Ord. 6746
Extra parking
None for ADUs under 1,000 sq ft of floor area (excluding garage) or within 1/2 mile of a major transit stop (as defined in RCW 36.70A.696); otherwise 1 off-street space per ADU, in addition to spaces required for the primary structureLUC 20.20.120.C.5, 20.20.120.B.1
Approval process
Permitted use

Residential use chart note 9: ADUs are permitted subject to LUC 20.20.120. Per LUC 20.20.120.C.2 the ADU is a subordinate use to the primary structure until use and occupancy are allowed under BCC 23.05.140 (certificate of occupancy), then it becomes a permitted use. Building permit via MyBuildingPermit; no conditional use permit.

LUC 20.10.440 Residential chart note 9; LUC 20.20.120.C.2
Rental restrictions
No ADU-specific rental restrictions in the Land Use Code; no minimum lease term. LUC 20.20.800 (Short Term Stay Uses) by definition applies only to PUD and multifamily dwelling units, not ADUs on single-family lots

Ord. 6746 also removed the prohibition on selling ADUs as condominiums, so separate ownership is possible.

LUC 20.20.120 (no rental provisions); LUC 20.20.800.A
The fine print: 6 caveats that can change the picture
  • Two ADUs per lot are allowed only in land use districts that permit a single-family dwelling on that lot (LUC 20.20.120.C.1).
  • Detached ADUs follow middle housing dimensional standards (LUC 20.20.538), with a 24 ft height cap (28 ft when built as an addition over an existing accessory structure) and alley lot-line siting allowed (LUC 20.20.120.E).
  • No new ADU is permitted on a unit lot created through a unit lot subdivision or short subdivision under LUC 20.45A/20.45B (LUC 20.20.120.C.7).
  • A site may not contain both an ADU and a business operating under a Home Occupation Permit (LUC 20.20.120.C.6).
  • Existing structures (e.g. detached garages) may be converted to ADUs even where the structure does not meet current setback or lot coverage requirements, without creating a nonconformity (LUC 20.20.120.C.4).
  • The Director may exceed the 1,200 sq ft cap in listed circumstances, so the size limit is not absolute (LUC 20.20.120.C.3.a).

Summarized from Bellevue's ordinance text, read July 2026; every row links the code section it came from. Rules often vary by zone and lot, so treat this as orientation, not a permit determination, and confirm with the planning department before you commit to a design.

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ADU regulations

Short-term rental rules

Planning to rent your ADU on Airbnb or VRBO? Bellevue regulates short-term rentals separately; check these before counting on nightly rental income.

Washington statewide law also applies

Washington sets baseline ADU rights at the state level. Where local rules are stricter than state law allows, state law usually wins, so both are worth reading.

See Washington statewide rules

Spotted something outdated?

Zoning codes change. If a link is dead or Bellevue has updated its ordinance, report it and we'll verify against the official source.

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