It is the purpose of this chapter to implement the policy provisions of the housing element of the city’s comprehensive plan by eliminating any unnecessary or onerous barriers to the location of accessory dwelling units in single-family residential zones and to provide for a more diverse and affordable housing stock while maintaining neighborhood quality. It is also the purpose of this chapter to provide owners of single-family dwelling units with a means of obtaining rental income, companionship, security, and services through tenants in either the accessory dwelling unit or the principal dwelling unit. (Ord. 2025-671 § 11).

A. “Accessory dwelling units” shall have the meaning stated in NMC 18.06.183.

B. “Property owner” shall mean the owner of the property as indicated by documents recorded with the King County department of records and elections. (Ord. 2025-671 § 11).

Up to two accessory dwelling units shall be permitted as subordinate to a single-family dwelling unit if the accessory dwelling unit meets the following requirements:

A. New or Existing Development. Accessory dwelling unit(s) shall be allowed in either an existing garage structure or an existing or a newly constructed single-family residence. Conversions to accessory dwelling units are allowed in nonconforming structures.

B. Size and Scale. An accessory dwelling unit shall be a minimum of 300 square feet and not more than 1,000 square feet in size; provided, that if an accessory dwelling unit is located completely on a single floor, the director of community development may allow the accessory dwelling unit to exceed these square footage requirements to the extent necessary to efficiently use all floor area.

C. Location. Accessory dwelling unit may be added to or included within the same structure as the principal dwelling unit, or the accessory dwelling unit may be located in a detached structure.

D. Height. Attached accessory dwelling units may be up to 30 feet in height, while detached accessory dwelling units are limited to 24 feet. Height for accessory dwelling units is calculated in the same manner as for primary unit single-family detached homes in NMC 18.12.030(B)(23).

E. Parking. One parking space is required per accessory dwelling unit, independent of parking requirements for the primary unit. Parking for accessory dwelling units and/or the primary unit may be collocated on a site for condominiums or a parent lot if a unit lot subdivision is in effect.

1. Off-street parking for accessory dwelling units are not required within one-half mile of a major transit stop.

F. Tenure. Accessory dwelling units may be either rented or sold as condominiums or fee simple within an approved unit lot subdivision.

G. Home Occupations. A site may not contain both an accessory dwelling unit and a Type II home occupation or a home industry, as defined in Chapter 18.30 NMC.

H. Compliance With Applicable Codes. The accessory dwelling unit shall comply with all standards as adopted by the city, including the construction codes as adopted and administered in NMC Title 15, and any other applicable codes or regulations, except as provided in this chapter. Except as provided in this chapter, the accessory dwelling unit shall comply with all zoning code provisions for single-family residences, including height and setbacks, and the accessory dwelling unit shall be included as part of the impervious surface and floor area limitations for a building site. (Ord. 2025-671 § 11).

The city shall not require that an accessory dwelling unit have a separate connection to any utility service facilities; provided, that the owner shall comply with any rules or regulations of the utility service provider regarding the connection of an accessory dwelling unit to the service provider’s facilities. (Ord. 2025-671 § 11).