Chapter 17.100
ACCESSORY DWELLING UNITS (ADUS)
Sections:
17.100.010 Purpose and intent.
17.100.030 Standards and criteria.
17.100.010 Purpose and intent.
The purpose of an accessory dwelling unit (ADU) is to:
A. Add affordable units to existing housing and make housing units available to moderate-income residents who might otherwise have difficulty finding homes within the city.
B. Provide homeowners with a means of obtaining, through tenants in either the accessory dwelling unit or the principal residence, rental income, companionship and/or security.
C. Protect neighborhood stability, property values and the single-family residential appearance of the neighborhood by ensuring that accessory dwelling units are installed under the conditions of this title. (Ord. 2083-24 § 1, 2025; Ord. 1954-20 § 1 (Exh. A)(part), 2020)
17.100.020 Permit required.
A development authorization application is required for all accessory dwelling units. Application for an ADU shall be made in accordance with the permit procedures established in Chapter 2.90. The director shall have the authority to approve accessory dwelling units (ADUs) which are consistent with the regulations and provisions herein. (Ord. 2083-24 § 1, 2025; Ord. 1954-20 § 1 (Exh. A)(part), 2020)
17.100.030 Standards and criteria.
Accessory dwelling units shall meet the following criteria:
A. Accessory dwelling units are subject to the codes, regulations, and statutes adopted by reference in Chapter 15.04. The design and size of the accessory dwelling unit shall conform to all applicable standards in the building, plumbing, electrical, mechanical, fire, health, and any other applicable codes. When there are practical difficulties involved in carrying out the provisions of this title, the director or a designee may recommend modifications that will meet the intent of these codes. Such modifications shall be processed as a variance under this title.
B. ADUs are permitted on lots in all zones that allow single-family residences. The lot must meet minimum lot size requirements for the principal residence and may not contain more than one primary dwelling unit.
C. Not more than two ADUs shall be permitted per lot.
D. An accessory dwelling unit may be attached or detached from the principal unit.
E. An accessory dwelling unit may be established in an existing single-family dwelling unit or in a detached structure on a legal building lot by any one or by a combination of the following methods:
1. Alteration of interior space of the dwelling; or
2. Conversion of an attic, basement, attached or detached private garage, or other previously uninhabited portion of a dwelling; or
3. Addition of attached living area onto an existing dwelling; or
4. Construction of a detached living area.
F. The maximum size of an accessory dwelling shall not exceed one thousand square feet. The maximum height of an ADU shall not exceed twenty-four feet; except the height of a structure containing an ADU over a garage (carriage house) may be increased to match the existing roof pitch of the primary residence, not to exceed thirty-five feet. If the height limitation on the primary residence is less than twenty-four feet, the maximum height of the ADU shall not exceed that limitation.
G. The minimum size of an accessory dwelling unit shall not be less than two hundred five square feet.
H. The accessory dwelling unit may be sited at a lot line if the lot line abuts a public alley, unless the city routinely plows snow on the public alley.
I. The accessory dwelling unit must have a separate entrance from the primary unit.
J. The ADU shall be billed as a unit for monthly city utility billing purposes. Utilities between the primary dwelling unit and the ADU may be shared and may require upgrades to be in compliance with utility regulations. In all cases, the utility service shut-offs must be accessible to occupants of both units.
K. On lots equal to or smaller than six thousand square feet, one off-street parking space is required per ADU, in addition to the off-street parking spaces required for the principal residence, before any zero lot line subdivisions (as applicable) or lot splits. On lots greater than six thousand square feet, two off-street parking spaces are required per ADU, in addition to the off-street parking spaces required for the principal residence, before any zero lot line subdivisions (as applicable) or lot splits. Off-street parking is not required for an ADU if the lot is located within one-half mile walking distance of a major transit stop, as defined in RCW 36.70A.030(25). Parking must be provided on the subject property, either off of an alley or on a driveway. When the property abuts an alley, the off-street parking space for the accessory dwelling unit shall gain access from the alley. Parking shall be developed in accordance with the standards in Chapter 17.36.
L. Spec homes may be constructed with an associated ADU, if in compliance with this chapter.
M. Recreational vehicles or temporary housing shall not be utilized as an accessory dwelling unit.
N. The accessory and principal dwelling units shall comply with all applicable requirements of the International Residential Code and zoning ordinance as adopted or amended by the city.
O. A permit for an accessory dwelling unit shall not be transferable to any lot other than the lot described in the application.
P. ADUs shall comply with the same design guidelines as the primary dwelling. The planning director may approve alternate design of detached ADUs if the proposed building meets the design standards for residential buildings in a planned residential development. This clause is intended to allow for ADU designs that are aesthetically interesting but may not resemble the architecture of the primary dwelling. There are many off-the-shelf ADU designs that provide a high level of aesthetic interest, but may not be similar to the primary dwelling.
Q. The address of the ADU(s) shall be the same as the main house with an “A” added to the end of the address number for the first ADU and a “B” added to the end of the address number for a second ADU. The address of the primary residence shall remain the same.
R. Short-term rentals are not permitted on properties with an accessory dwelling unit. (Ord. 2083-24 § 1, 2025; Ord. 2096-25 § 1, 2025; Ord. 2043-23 § 1 (Exh. A), 2023; Ord. 1954-20 § 1 (Exh. A)(part), 2020)