Shoreline, WA Accessory Structures: ADU Rules (2026)
ADU rules in Shoreline, WA, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.
Key Facts
- Max ADUs per lot
- Two, subject to Table 20.50.020(1) density
- Size cap
- 1,200 square feet (interior exception applies)
- Location
- Attached, within main structure, or detached
- Governing section
- Shoreline Municipal Code § 20.40.210
- Enforcement
- Notice and order, $500+ civil penalty
Summary
In the City of Shoreline, homeowners can build up to two accessory dwelling units per lot under Shoreline Municipal Code § 20.40.210, subject to the density formula in Table 20.50.020(1). Each ADU can share the primary structure or stand detached, but is capped at 1,200 square feet unless it qualifies for the interior-unit exception. All ADUs must meet the City's building and zoning codes.
A. Two accessory dwelling units per lot subject to the max density calculations in Table 20.50.020(1). B. Accessory dwelling units may be located in the same structure as a principal dwelling unit, or in a detached structure. C. Accessory dwelling units shall not be larger than 1,200 square feet. Exception to SMC § 20.40.210(C): An accessory dwelling unit interior to the residence may be larger than 1,200 square feet where the unit is located on a separate floor and shares a common roof with the primary residence. D. Accessory dwelling unit shall comply with all applicable codes and standards.
Full Breakdown
Shoreline Municipal Code § 20.40.210 governs accessory dwelling units (ADUs) citywide, permitting up to two ADUs per lot in addition to the principal dwelling, with the maximum allowable density set by the calculations in Table 20.50.020(1) of the Development Code. An ADU can be attached, built within the same structure as the main house, or constructed as a fully detached structure on the same lot; the code does not require the two forms to match. Size is capped at 1,200 square feet under subsection C, but Shoreline carves out one exception: an ADU built inside the residence can exceed 1,200 square feet if it occupies a separate floor and shares a common roof with the primary dwelling, recognizing basement or upper-floor conversions that do not add new building footprint.
Subsection D requires every ADU to comply with all applicable codes and standards, which pulls in Chapter 15.05 SMC's adopted building and fire codes plus the Development Code's parking, setback and design requirements for the zone. Applications run through the Planning and Community Development Department under the permit procedures in Chapter 20.30 SMC. A property owner who builds or rents an ADU that does not conform to § 20.40.210, or without the required permits, is subject to the code enforcement process in SMC § 20.30.760, including a notice and order and civil penalties, and can face a misdemeanor citation under § 20.30.770(B) for willful violations. Appeals of a notice and order go to the Hearing Examiner within 14 days of service under SMC § 20.30.790.
Violations & Fines
Building or occupying an ADU that exceeds the 1,200-square-foot cap, or without permits, triggers a Director's notice and order under SMC § 20.30.760. Civil penalties start at $500 for the first 14 days after the compliance deadline passes, rising to 150 percent for the next 14 days and doubling every period after that under § 20.30.770(D). Willful violations are a misdemeanor punishable by up to a $1,000 fine and 90 days in jail under § 20.30.770(B).
Frequently Asked Questions
How many accessory dwelling units can I build on my Shoreline property?
Is there a size limit for a Shoreline ADU?
What happens if my ADU does not meet code?
Sources & Official References
Other rules in Shoreline
How Shoreline compares: Easiest Cities to Build an ADU·Compare Shoreline to another location·View the Washington accessory structures overview
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ADU Rules in Nearby Cities
How other cities in King County handle adu rules.