Title 17C Land Use Standards
Chapter 17C.300 Accessory Dwelling Units
Section 17C.300.130 Development Standards
- Development Standards – Requirements for All Accessory Dwelling Units.
All accessory dwelling units must meet the following:
- Creation.
An accessory dwelling unit may only be created through the following methods:
- Converting existing living area, attic, basement or garage.
- Adding floor area.
- Constructing a detached accessory dwelling unit on a site with an existing residential use.
- Constructing a residential use with an internal or detached accessory dwelling unit.
- In the R1, R2, RMF, or RHD zone, constructing an attached or detached accessory dwelling unit on a site with any existing or new principal structure (including non-residential uses or structures). Any structure shall comply with all applicable building, fire, and engineering standards.
- Number of Residents.
The total number of individuals that reside in all units on the site may not exceed any lawful limits on occupant load per square foot or generally applicable health and safety provisions as established by applicable building or fire code, as provided in RCW 35.21.682.
- Location of Entrances for Internal ADUs.
Only one entrance may be located on the facade of the structure facing the street, unless the principal structure contained additional entrances before the accessory dwelling unit was created. An exception to this regulation is entrances that do not have access from the ground such as entrances from balconies or decks.
- Parking.
- Studio and one-bedroom ADUs require no additional parking. One additional off-street parking space is required for the accessory dwelling unit with more than one bedroom, plus one per bedroom after two bedrooms. Existing required parking for the principal structure must be maintained.
- As an exception to subsection (a), no additional off-street parking space is required for the ADU within one-quarter-mile of stops for a bus or other transit mode providing actual fixed route service at intervals of no less frequently than fifteen minutes for at least five hours during the peak hours of operation on weekdays, defined as a major transit stop under RCW 36.70A.696.
- Additional Development Standards for Detached ADUs.
- Setbacks.
Except for conversion of existing accessory structures, the accessory dwelling unit must be:
- as specified for setbacks in Table 17C.111.205-2 for accessory structures and
- Height.
The maximum height allowed for a detached accessory dwelling unit is provided in Table 17C.111.205-2.
- Bulk Limitation.
The building coverage for the detached accessory dwelling unit may not be larger than the building coverage of the principal structure.
- On lots five thousand five hundred square feet or larger, the combined building coverage of all detached accessory structures may not exceed fifteen percent of the total area of the site.
- On lots smaller than five thousand five hundred square feet, the combined building coverage of all detached accessory structures may not exceed twenty percent of the total area of the site.
- Conversion of Existing Detached Accessory Structures.
- Conversion of an existing detached accessory structure that is in a front building setback required by Table 17C.111.205-2 is not allowed. Conversion of an existing detached accessory structure that is in a rear or side building setback is allowed as provided by SMC 17C.111.235, Setbacks, and SMC 17C.111.240, Accessory Structures.
- If the accessory dwelling unit is proposed for an existing detached accessory structure that meets any of the standards of subsections (B)(2) and (3) of this section, alterations that will move the structure out of conformance with the standards that are met are not allowed.
- If the accessory dwelling unit is proposed as a conversion of an existing detached accessory structure or a portion of the building, and any floor area is added to the existing detached accessory structure to accommodate an ADU, then the entire structure must meet the underlying zoning development standards.
- Utilities and Addressing.
The ADU must utilize those municipal utilities and address established for the principal dwelling unit.
- Code Compliance.
The ADU must meet all technical code standards of this title including building, electrical, fire, and plumbing code requirements and permits.
Date Passed: Monday, November 20, 2023
Effective Date: Monday, January 1, 2024
ORD C36459 Section 27
