The purpose of this chapter is to allow for residential accessory structures to be established which are incidental to the primary residential use of a single-family residence or middle housing residence, while ensuring compatibility with surrounding residential uses. The accessory structure must be clearly subordinate to the primary use. Accessory structures or uses may not be established until the principal structure is constructed on the property.
(Ord. 3351 § 5 (Exh. A), 2025; Ord. 3367 § 1 (Exh. A), 2025)
In the zones in which a residential accessory structure is listed as a permitted use, the community development director or designee shall review all proposals for accessory structures. The following standards and regulations shall apply to all proposed accessory structures.
(1) 
Table 1
Front setback
See MMC § 22C.010.080 for standard lots and MMC § 22G.080.080 for PRD lots.
Side setback
5 feet
Side street setback
10 feet along nonarterials; 15 feet along arterials
Rear yard setback 1, 2, 3
5 feet (one-story structure); 10 feet (when the entrance faces the rear yard or for two-story or greater structure in PRDs); 15 feet (two-story structure or when accessory structure entrance faces an alley with right-of-way less than 10 feet wide) 4
Building and impervious coverage
See MMC § 22C.010.080 for standard lots or MMC § 22G.080.080 for PRD lots
Accessory structure footprint 5
On lots under one acre, accessory structures are further limited to 80 percent of the footprint of the primary residence. 6
Height
20 feet (lots under one acre) 6; or 30 feet (lots over one acre, or lots under one acre where the accessory structure contains an accessory dwelling unit)
Notes:
1 Accessory structures in planned residential developments are subject to the rear yard setbacks set forth in MMC § 22G.080.080.
2 No more than 50 percent of the required rear setback area (i.e., back 20 feet of the lot) may be covered with accessory structures.
3 An accessory structure which is located in the rear setback area may be attached to the principal structure; provided, that no portion of the principal structure is located within the required yard setbacks for principal structures in the zone.
4 The increased alley setback applies to vehicle access points from garages, carports, fenced parking areas or other accessory structure. Exception: in the downtown neighborhood, the rear setbacks outlined in the table above may be reduced to two feet from the rear lot line; provided, that the alley right-of-way is a minimum of 20 feet in width. Where the alley right-of-way is less than 20 feet in width, the property owner shall be required to dedicate to the city sufficient property to widen the abutting alley to the full width as measured from the design centerline, to conform to the applicable road standards specified by the city engineer. Upon dedication of the necessary right-of-way, the rear setback may be reduced to two feet from the rear lot line. Where an existing, nonconforming structure located in the downtown neighborhood is internally remodeled to include an accessory dwelling unit, but the footprint of the structure is not increased, the structure can be allowed to remain at a zero setback; provided, that the right-of-way is 20 feet in width.
5 The community development director is specifically authorized to allow an increase in the size of a detached accessory structure over the requirements outlined in this table; provided, that the accessory structure(s) shall be compatible with the principal structure and/or neighborhood character. To make this determination, the community development director may consider such factors that include, but are not limited to, view obstruction, roof pitch, building materials, screening and landscaping, aesthetic impact on surrounding properties and streetscape, incompatible scale with dwellings on surrounding properties, and impact on neighborhood character. The community development director shall also have the authority to impose greater setback requirements, landscape buffers, or other locational or design requirements to mitigate the impacts of accessory structures which are greater in size than otherwise allowed by this section.
6 The community development director may allow minor deviations to the 20-foot height and the 80 percent building footprint limitations applicable to properties under one acre as necessary to accommodate industry standards for building dimensions.
(2) 
A detached garage, carport or other permitted accessory structure may be in the front or side yard, or on the flanking street side of a corner lot, only if the applicant demonstrates to the satisfaction of the community development director that:
(a) 
The accessory structure is consistent with the architectural character of the residential neighborhood where it will be located, and the principal structure on the lot; and
(b) 
The accessory structure shall have a roof pitch similar to the principal structure and have siding and roofing materials similar to or compatible with those used on the principal structure. No metal siding or roofing shall be permitted unless it matches the siding and roofing of the principal structure, or unless it is a building material that is of a residential character such as metal tab roofing or other products consistent with standard residential building materials. Plans for the proposed accessory structure(s) indicating siding and roofing materials shall be submitted with the application.
(Ord. 3351 § 5 (Exh. A), 2025; Ord. 3367 § 1 (Exh. A), 2025)