The purpose of allowing and regulating accessory dwelling units (ADUs) in residential neighborhoods pursuant to this chapter is to promote affordable housing and a range of housing types, to encourage increased density within existing neighborhoods without significantly changing the character of the neighborhoods, and to provide the opportunity for homeowners to gain the extra income necessary to help meet the rising costs of home ownership.

(Ord. 729 § 2 (Exh. B) (part), 2007)

(Ord. No. 815, § 2, 10-2-2012; Ord. No. 25-1006, § 1(Att. A), 1-22-2025)

ADUs are permitted in all single-family zones and in the R12 zone, subject to the requirements of this chapter and all requirements of Title 15. No more than two ADUs shall be allowed per lot. No ADU will be permitted on the same lot as any duplex or multifamily dwelling.

(Ord. 729 § 2 (Exh. B) (part), 2007)

(Ord. No. 25-1006, § 1(Att. A), 1-22-2025)

A.

Code Compliance. ADUs shall meet all development standards for the applicable zone, except as modified by this chapter, and shall comply with all applicable city regulations, including but not limited to the building code.

B.

Size. ADU size shall be no more than fifty percent of the principal residence's size when the principal residence is more than 2,000 square feet. For principal residences less than 2,000 square feet, the ADU may be up to 1,000 square feet.

C.

Parking. Separate and apart from the parking requirements applicable to the principal residence, one off-street parking space is required for each ADU; provided that on-site parking is not required for ADUs within one-half mile of a major transit stop.

D.

Walkway. Each ADU shall be serviced by a pedestrian walkway connecting the adjacent street or alley to the primary entrance of the ADU.

E.

Bedrooms. No more than two bedrooms shall be located within an ADU.

F.

Nonconformance. No permit shall be issued for a nonconforming ADU unless and until the structure is brought into conformance with all applicable current regulations.

G.

Mobile Homes. No mobile home, recreational vehicle, camper or vehicle shall be used as an ADU.

H.

Specific provisions for accessory dwelling units are set forth in the impact fee regulations codified at Title 3 CMC and the utility regulations codified at Title 13 CMC. ADUs under this chapter shall comply with all such regulations, as well as any and all other applicable requirements, specifically including without limitation the King County regulations regarding wastewater capacity charges.

(Ord. 729 § 2 (Exh. B) (part), 2007)

(Ord. No. 815, § 3, 10-2-2012; Ord. No. 25-1006, § 1(Att. A), 1-22-2025; Ord. No. 25-1010, § 1(Exh. A), 4-1-2025)

In addition to all of the standards described in CMC Section 15.46.030, Attached ADUs must also comply with the following:

A.

Entrance. Only one entrance for the entire residential structure may be visible from any street.

B.

Design. Each attached ADU shall be designed so that, to the degree reasonably feasible, the appearance of the building remains that of a single-family residence. At a minimum, the architecture of each attached ADU should conform to the following guideline:

1.

Any new exterior construction associated with creating an attached ADU should match the existing exterior materials, color and design of the principal residence;

2.

The pitch of the attached ADU's roof should match that of the principal residence within a twenty-degree range;

3.

Window styles should be similar to that of the original house in size, shape, trim color and the number of panes.

(Ord. 729 § 2 (Exh. B) (part), 2007)

(Ord. No. 25-1006, § 1(Att. A), 1-22-2025)

In addition to all of the standards contained in CMC Section 15.46.030, detached ADUs must also comply with the following:

A.

Height. The maximum height of a detached ADU shall be twenty-five feet.

B.

Reserved.

C.

Setbacks. Detached ADUs are subject to the same setback regulations as single-family detached dwelling units and garages that apply in the underlying zoning district, unless otherwise provided by this title.

D.

The detached ADU should be similar to the principal residence with regard to:

1.

Exterior materials, color and design;

2.

Roof pitch should match that of the principal residence within a twenty-degree range;

3.

Window styles including size, shape, trim color and number of panels.

(Ord. 729 § 2 (Exh. B) (part), 2007)

(Ord. No. 25-1006, § 1(Att. A), 1-22-2025)

A.

Each ADU shall require an application for accessory dwelling unit permit subject to the Type I permit review process [CMC 15.09.020 and CMC 15.09.050].

B.

In addition to the accessory dwelling unit permit application, an application for an ADU shall include:

1.

Site plan showing location of the proposed ADU, parking spaces for the ADU and principal residence, vehicular access for the ADU, pedestrian walkway to serve the ADU, and location of principal residence and any other structures on the lot. The site plan should also show the required building setbacks for the underlying zone.

2.

Size in square feet of the floor areas of the proposed ADU and the principal residence.

3.

Building plans showing the lay-out of the proposed ADU, specifying the number and location of all bedrooms.

4.

Elevations that show the ADU and the principal residence, illustrating the exterior construction, roof pitch, window styles and colors of the proposed ADU and specifying dimensions including building heights.

(Ord. 729 § 2 (Exh. B) (part), 2007)

(Ord. No. 25-1006, § 1(Att. A), 1-22-2025)