How many ADUs can I build, and how big?
✓ Verified against code · August 19, 2026
Two per lot in any configuration — including converting an existing detached garage — at 1,000 sq ft each (an internal ADU may be the larger of 50% of the house or 1,000 sq ft).
Citation: SMC 21.05.010.C(5)(a)
How current is this?
Sammamish’s ADU rules run under SMC 21.05.010.C(5) / 21.04.030.C (Sammamish Municipal Code) (Ordinance O2024-578). Sammamish's Title 21 rewrite (Ord O2024-578) took effect January 1, 2025 — six months ahead of the state deadline. Beware the city's own DADU handout: last revised September 2023, it still shows an 18-ft height limit, one-DADU cap, and two-space parking rule, all long repealed. We verified this answer against primary sources on August 19, 2026, and every change we catch is logged in the changelog.
More Sammamish ADU questions
- Does a Sammamish ADU count against my floor-area (FAR) limits?
- How tall can a Sammamish DADU be?
- Do I need parking for a Sammamish ADU?
- How close to the lot line can my DADU sit?
All Sammamish ADU rules → · Compare Washington cities →
Not legal advice — lot-specific overlays can change the answer for your parcel. The citation above points at the governing code section; check it, or ask the city to confirm.