Accessory dwelling units are permitted uses in the R-1 zoning district, subject to the requirements set forth in this chapter and the requirements of the individual zone. In the event that the applicable regulations conflict, this chapter shall control. (Ord. 1019 § 1 (Exh. A), 2025; Ord. 805 § 1, 1999; Ord. 706 § 2, 1994)

All legally nonconforming accessory dwelling units may be maintained after the effective date of this chapter without compliance with its requirements, subject to the provisions of Chapter 17.60 CHMC, Nonconforming Uses. Any other nonconforming accessory dwelling units existing at the time of adoption of this chapter must comply with the requirements set forth herein or be subject to an enforcement action under Chapter 17.80 CHMC, after February 1, 1995. (Ord. 1019 § 1 (Exh. A), 2025; Ord. 805 § 1, 1999; Ord. 706 § 2, 1994)

A. Compliance With Applicable Codes. An accessory dwelling unit shall meet the requirements of all other applicable zoning and building codes, including, but not limited to, the city’s building and fire code and minimum lot coverage, size, and setbacks.

B. Certification by City of Bellevue Utilities Department. A certification must be provided by the Bellevue utilities department that the water supply and sewage disposal facilities for the accessory dwelling unit are adequate to serve the unit.

C. Attached or Detached Accessory Dwelling Unit. An accessory dwelling unit may be an attached (AADU) or detached (DADU) accessory dwelling unit.

D. Limitation on Number of Accessory Dwelling Units. Up to two accessory dwelling units may be created on lots with a single-family dwelling. If a lot is developed with a middle housing unit, then no accessory dwelling unit is permitted on that lot.

E. Location and Lot Restrictions. Accessory dwelling units may not be constructed on any lot that contains critical areas or buffers.

F. Size Restrictions. The accessory dwelling may not exceed 1,000 square feet of gross floor area. The maximum height may not exceed 25 feet.

G. Off-Street Parking. Accessory dwelling units must maintain the following minimum off-street parking spaces:

1. Two stalls per accessory dwelling unit on lots greater than 6,000 square feet before any unit lot subdivisions or lot splits.

2. One stall per accessory dwelling unit on lots less than 6,000 square feet before any unit lot subdivisions or lot splits.

3. Any off-street parking required for an accessory dwelling unit must be in addition to any off-street spaces required for the single-family, principal dwelling, pursuant to Chapter 17.52 CHMC.

4. Exception. Within a one-half mile walking distance from a major transit stop, as defined in RCW 36.70A.696, off-street parking for accessory dwelling units is not required. The walking distance must be calculated using a pathfinding method.

H. Conversion of Existing Structures to ADU. An existing structure, including attached or detached garages, may be converted into an accessory dwelling unit. If converting a garage to an accessory dwelling unit, the required minimum number of off-street parking spaces must be maintained, per this chapter and Chapter 17.52 CHMC.

1. Existing Nonconforming Structure Conversion. A structure that does not conform to current setback or lot coverage standards may be converted to an accessory dwelling unit, or its existing footprint may be used for such a conversion. However, the conversion must comply with all other applicable regulations, including maximum ADU size limits.

I. Separate Address. The accessory dwelling unit shall have a separate numbered address as established by the city.

J. Setback Requirements for Accessory Dwelling Units.

1. The reduced rear yard setback requirements for accessory buildings as stated in CHMC 17.16.060 shall not apply to accessory dwelling units.

2. Alley Setback Exception. For lots located along public alleyways not routinely snow-plowed, an accessory dwelling unit may be sited at the lot line adjacent to the alley. This exception does not apply to private lanes and alleys. (Ord. 1019 § 1 (Exh. A), 2025; Ord. 819 § 1, 2000; Ord. 805 § 1, 1999; Ord. 745 § 1, 1996; Ord. 706 § 2, 1994)

A. Application Requirements. Any property owner seeking to establish an accessory dwelling unit must submit an application to the public works director on forms provided by the city. The application must be processed in accordance with the established permit type under CHMC Title 19.

B. Inspection by Public Works Director – Approval. After receipt of a complete application form and prior to approval of any accessory dwelling unit, the public works director must inspect the property to confirm that the standards of this chapter are satisfied. If these standards are met, the accessory dwelling unit must be approved.

C. Registration. The property owner must file a completed registration application form agreeing to the standards within this chapter. After approval, the registration form or other form as required by the public works director shall be recorded against the property with the King County department of records and elections.

D. Cancellation of Registration. Cancellation of the accessory dwelling unit’s registration may be accomplished by the property owner’s filing a certificate with the public works director for recording at the King County department of records and elections, or may occur as a result of enforcement action.

E. Fees, Costs to Be Paid by Applicant. An application fee shall accompany the application described in subsection (A) of this section, which fee shall be determined by resolution of the city council. The property owner shall also be responsible to pay all recording and filing costs attributable to establishment, maintenance or cancellation of an accessory dwelling unit. The cancellation certificate will confirm that the residence has reverted to use as a single-family dwelling unit. (Ord. 1019 § 1 (Exh. A), 2025; Ord. 805 § 1, 1999; Ord. 706 § 2, 1994)