Accessory dwelling units (ADUs) are intended to:

A.

Provide for a range of housing choices in the city, including rental and ownership options;

B.

Provide additional dwelling units, thereby increasing densities with minimal cost and disruption to existing neighborhoods;

C.

Allow individuals and smaller households to retain large houses as residences;

D.

Enhance options for families by providing opportunities for older or younger relatives to live in close proximity while maintaining a degree of privacy; and

E.

Ensure that the development of an ADU does not cause unanticipated impact on the character or stability of single-family neighborhoods.

(Ord. 2515 § 1 (Exh. A (part)), 2008: Ord. 2443 § 3 (Exh. A (part)), 2006)

(Ord. No. 19-012, § II(Exh. A), 11-4-2019; Ord. No. 25-025 meeting, § I (Exh. A), 12-15-2025)

ADUs shall meet the requirement of this chapter, and may be allowed in all zones where residential uses are permitted.

(Ord. 2515 § 1 (Exh. A (part)), 2008: Ord. 2443 § 3 (Exh. A (part)), 2006)

(Ord. No. 19-012, § II(Exh. A), 11-4-2019; Ord. No. 25-025 meeting, § I (Exh. A), 12-15-2025)

ADUs are allowed in the following configurations and conditions:

A.

Attached ADUs, such as in a basement, attic, or garage; or

B.

Detached ADUs, which may be comprised of either one or two detached structures; or

C.

A combination of one attached ADU and one detached ADU.

D.

ADUs may be converted from existing legal accessory structures.

E.

Individual ADUs can be conveyed separately as condominium units per Chapter 64.34 RCW or can be divided into unit lots.

(Ord. 2515 § 1 (Exh. A (part)), 2008: Ord. 2443 § 3 (Exh. A (part)), 2006; (Ord. No. 2691, § I(Exh. A), 1-21-2014; Ord. No. 19-012, § II(Exh. A), 11-4-2019; Ord. No. 25-025 meeting, § I (Exh. A), 12-15-2025)

Editor's note— ; Ord. No. 25-025 meeting, § I (Exh. A), adopted December 15, 2025, renumbered the former §§ 18.27.040—18.27.060 as §§ 18.27.030—18.27.050. The historical notation has been retained with the amended provisions for reference purposes.

A.

Number. No more than two ADUs in any configuration shall be allowed in residential zoning districts with a principal unit. ADUs count towards the unit densities of Chapter 18.25 Middle Housing, so that two ADUs are allowable only if a lot is improved with only one principal dwelling unit.

B.

Building Permit. The applicant must apply for a building permit for an ADU. An ADU shall comply with applicable building, fire, health, and safety codes. Addressing of the ADU shall be assigned by the building department. An ADU cannot be occupied until a certificate of occupancy is issued by the building department.

C.

Conformance to Zoning. The addition of an ADU shall not make any lot, structure or use nonconforming within the development site. An ADU shall conform to existing requirements for the primary residence, unless stated otherwise in this chapter. ADUs converted from existing accessory structures may be nonconforming to current setback and lot coverage requirements.

D.

Height. Building height is limited to twenty-four feet for a detached ADU. Building height requirements of the underlying zone apply to the ADU for internal conversion, or structural addition to the existing primary dwelling.

E.

Setbacks. An ADU unit shall comply with the front yard setback. A detached ADU shall not be located closer than five feet to a side or rear lot line, or not closer than ten feet to a side lot line along a flanking street of a corner lot. A detached ADU does not require a setback from any rear lot line that abuts a public alley.

F.

Total Floor Area. The total gross floor area of an ADU shall not exceed one thousand square feet. The Director may allow an increase in floor area when an ADU is completely located on a single floor within the footprint of an existing residential unit or accessory structure in order to allow for efficient use of existing floor area.

G.

Parking. An ADU shall have a minimum of one off-street parking space, in addition to the off-street parking required for the other residential units on the same lot. This requirement does not apply to ADUs located within one-half mile of a major transit stop.

H.

Utilities. An ADU shall connect to public sewer and water. A home or lot not connected to public sewer and water, which adds an ADU, shall connect to public sewer and water. An ADU may share water and sewer connections with the primary unit only when the meter, service lines, and any STEP/STEF tank are adequately sized to serve the primary unit and ADU. ADUs that are or will be separately owned shall maintain fully independent utility services.

(Ord. 2515 § 1 (Exh. A (part)), 2008: Ord. 2443 § 3 (Exh. A (part)), 2006)

(Ord. No. 19-012, § II(Exh. A), 11-4-2019; Ord. No. 25-025 meeting, § I (Exh. A), 12-15-2025)

Editor's note— See Editor's note in § 18.27.030.

A.

Architectural Design. Detached ADUs must incorporate at least two of the following elements found on the principal dwelling unit(s):

1.

Roof overhang of the same depth

2.

Same roof pitch

3.

Trim of the same dimension and style

4.

Matching window proportions, grille patterns, and color

5.

Same primary paint color

6.

Same roofing material and color

7.

Similar porch or entryway detailing

8.

Same primary siding material

B.

Privacy. ADUs shall be designed and located to minimize disruption of privacy and outdoor activities on adjacent properties. Strategies to accomplish this include, but are not limited to:

1.

Stagger windows and doors to not align with such features on abutting properties.

2.

Avoid upper-level windows, entries and decks that face common property lines to reduce overlook of a neighboring property.

3.

Install landscaping as necessary to provide for the privacy and screening of abutting property.

C.

Any and all design requirements, limits, or restriction that apply to the principal unit shall also apply to ADUs.

(Ord. 2515 § 1 (Exh. A (part)), 2008: Ord. 2443 § 3 (Exh. A (part)), 2006)

(Ord. No. 2612, § I(Exh. A), 2-7-2011; Ord. No. 2691, § I(Exh. A), 1-21-2014; Ord. No. 19-001, § I(Att. A), 1-22-2019; Ord. No. 19-012, § II(Exh. A), 11-4-2019; Ord. No. 24-007, § II (Exh. A), 5-6-2024; Ord. No. 25-018 meeting, § I—III, 11-3-2025; Ord. No. 25-025 meeting, § I (Exh. A), 12-15-2025)

Editor's note— See Editor's note in § 18.27.030.

A.

Exterior Finish Materials. Exterior finish materials must duplicate or reflect the exterior finish material on the primary dwelling unit.

B.

Roof Slopes. For buildings over fifteen feet in height, the slope of the accessory dwelling unit roof must be the same as that of the predominate slope of the primary dwelling structure.

C.

Historic Structures. If an accessory dwelling unit is on the same lot as, or within an historic structure which has been designated on the national, state, or local historic register, the following design guidelines are applicable:

1.

Exterior materials shall be of the same type, size, and placement as those of the primary dwelling structure.

2.

Trim on edges of elements of an ADU shall be the same as those of the primary structure in type, size, and placement.

3.

Windows in any elevation which faces a street shall match those in the primary structure in proportion, i.e., same height, width, and orientation (horizontal or vertical).

4.

Pediment and Dormers. Each accessory dwelling unit over twenty feet in height shall have either a roof pediment or dormer, if one or the other of these architectural features are present on the primary dwelling.

(Ord. 2515 § 1 (Exh. A (part)), 2008: Ord. 2443 § 3 (Exh. A (part)), 2006)