The purposes of the accessory dwelling unit (ADU) regulations are to: implement the policy provisions of the housing element of the comprehensive plan by eliminating barriers to accessory dwelling units in residential neighborhoods and provide for affordable housing; provide homeowners with a means of obtaining rental income, companionship, security and services through tenants in either the accessory dwelling unit or principal unit; protect neighborhood character and stability by ensuring ADUs are compatible with surrounding land uses.

(Ord. 1056 § 1 Exh. A (part), 2007)

(Ord. No. 1336, § 2(Exh. A), 6-5-2025)

Two ADUs are permitted as an accessory use to a principal dwelling unit in the R4, R4.5, R6, R8, R12, R20, and MU12 zones, provided that the criteria presented in this chapter are met.

(Ord. 1056 § 1 Exh. A (part), 2007)

(Ord. No. 1336, § 2(Exh. A), 6-5-2025)

When ADUs are permitted as an accessory use, the following requirements shall be met:

A.

A maximum of two ADUs shall be permitted per principal dwelling unit. ADUs are exempt from the density requirements of the underlying zone.

B.

The total number of occupants in the ADU shall not exceed the maximum number established by the definition of family in DMC Chapter 14.06;

C.

ADUs may be attached to or detached from, the principal unit. The accessory dwelling unit shall comply with all applicable requirements of the underlying zone, except that:

1.

Detached accessory dwelling units may be located at a lot line if the lot line abuts a public alley.

2.

Accessory dwelling units may be converted from existing structures, including but not limited to detached garages, even if they violate current code requirements for setbacks or lot coverage.

D.

ADUs may be subdivided or otherwise segregated in ownership from the primary dwelling unit. The sale or other conveyance of a condominium unit independent of a principal unit may not be prohibited solely on the grounds that the condominium unit was originally built as an accessory unit.

E.

A detached ADU shall not exceed one thousand (1,000) square feet of gross floor area.

F.

An ADU that is part of an existing house shall not exceed one thousand five hundred (1,500) square feet of gross floor area. If an ADU occupies an entire single floor, the director may allow for an increase in the allowed size of the ADU in order to efficiently use all of the floor area, so long as all other standards of this chapter are met;

G.

An ADU is permitted above detached garages, or attached garages, if the ADU area is not in excess of one thousand five hundred (1,500) square feet. If an ADU occupies an entire single floor, the director may allow for an increase in the allowed size of the ADU in order to efficiently use all of the floor area, so long as all other standards of this chapter are met;

H.

A detached ADU shall be limited to a maximum building height of 24 feet as measured to the eave. See DMC Section 14.64.130 for calculating building height. An ADU located within the principal dwelling unit may meet the height of the zone.

I.

One off-street parking space shall be provided for the ADU, in addition to the number of spaces required for the primary dwelling unit. Parking spaces shall be paved with materials as deemed acceptable by the director, and may include garages, carports, driveways or other off-street areas reserved for vehicles;

J.

All ADUs shall comply with the design requirements of Title 14, Unified Development Regulations as they pertain to the primary dwelling unit on a parcel. No additional restrictions exceeding those required for the principal dwelling unit shall be required.

K.

If applicable, the portion of a single-family dwelling in which an ADU is proposed shall comply with all standards for health and safety contained in all applicable codes, such as building, plumbing, electrical, mechanical, fire and health, with the exception for ceiling height requirements of the International Residential Code (IRC). The building official may waive the ceiling height requirements of this chapter if it is determined that the structure was built in compliance with past building code requirements. The ADU shall comply with all DMC provisions for single-family dwellings including height, setbacks, and design standards, and the ADU shall be included as part of the impervious surface and floor area limitations for a building site.

(Ord. 1056 § 1 Exh. A (part), 2007)

(Ord. No. 1336, § 2(Exh. A), 6-5-2025)

A.

An applicant seeking to build an Accessory Dwelling Unit shall apply for an ADU permit with the building department. The application shall include an affidavit signed by the property owner agreeing to all the general requirements outlined in this section. An applicant seeking to build an ADU shall file a notice approved by the department with the King County department of records and elections that identifies the dwelling unit as accessory. The notice shall run with the land. The applicant shall submit proof that the notice was filed before the department shall approve any permit for construction of the ADU. The required contents and form of the notice shall be set forth by the director.

B.

If the owner intends to sell an Accessory Dwelling Unit, a notice of intent to sell must be submitted to the City 60 days prior to sale.

(Ord. 1056 § 1 Exh. A (part), 2007)

(Ord. No. 1336, § 2(Exh. A), 6-5-2025)

Impact and connection fees shall be determined by the City's adopted Fee Resolution.

(Ord. 1056 § 1 Exh. A (part), 2007)

(Ord. No. 1336, § 2(Exh. A), 6-5-2025)

Elimination or cancellation of a registered ADU may be accomplished by the owner filing a certificate with the King County department of records. Elections and licensing services, stating that the ADU no longer exists on the property. Cancellation may also result from an enforcement action by the city. The ADU structure may be converted to another permitted or accessory use or permanently removed from the property.

(Ord. 1056 § 1 Exh. A (part), 2007)

(Ord. No. 1336, § 2(Exh. A), 6-5-2025)