Kirkland, WA Accessory Structures: ADU Rules (2026)

07 permits two Accessory Dwelling Units (ADUs) per single-family dwelling: either one attached and one detached, or two of the same type. An ADU does not count as a separate 'dwelling unit' under the one-detached-unit-per-lot rules that otherwise apply in Chapters 15 through 56 KZC. Each ADU is capped at 1,200 square feet of gross floor area, though the Planning and Building Director may allow more square footage for an attached ADU that fits entirely within existing floor area on a single floor. Excluded from that square footage count: space under five feet of ceiling height, uncovered rooftop decks and at-grade patios, and up to 200 square feet of covered or uncovered exterior elements.

ADUs must generally meet the same setbacks, height limits, and lot coverage as the main house, though converting an existing structure like a detached garage into an ADU is exempt from current setback and lot coverage rules as long as it doesn't increase existing nonconformities. Parking is relaxed near transit: no off-street parking is required within a half-mile of a major transit stop, and even beyond that only one space is required when a lot has more than one ADU, unless on-street parking sits within 600 feet or 15-minute headway transit service is within a half-mile.

Permitting runs through the Planning and Building Department: the owner submits an application with a signed affidavit, and if no building permit is needed, a registration form and a property covenant recorded with the King County Recorder's Office are required instead. An unpermitted ADU created without a finaled building permit requires a physical inspection before an ADU permit can issue. Planning Official decisions are appealable under Chapter 145 KZC.