Sammamish ADU rules
✓ Verified against code · August 19, 2026
Current rules under SMC 21.05.010.C(5) / 21.04.030.C (Sammamish Municipal Code), adopted by Ordinance O2024-578, in effect since January 1, 2025. 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last revised September 2023, it still shows an 18-ft height limit, one-DADU cap, and two-space parking rule, all long repealed.
Common questions, answered from the code
Does a Sammamish ADU count against my floor-area (FAR) limits?
No — ADUs on single-family lots are exempt from both FAR and hardscape-coverage calculations. That's the opposite of Seattle's January 2026 rule, and it makes Sammamish one of the friendliest cities in the region for adding a DADU to an already-large home.
SMC 21.04.030.C · Permalink
How tall can a Sammamish DADU be?
24 feet in every residential zone. The city's own 2023 handout still says 18 feet — it predates the January 2025 rewrite and hasn't been updated.
SMC 21.04.030.C · Permalink
Do I need parking for a Sammamish ADU?
Usually not: no additional space if your parcel already has four or more, and no minimum at all within a quarter mile of an existing — or even a planned — transit stop.
SMC 21.05.010.C(5)(a)(iv); 21.06.030 · Permalink
How many ADUs can I build, and how big?
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).
SMC 21.05.010.C(5)(a) · Permalink
How close to the lot line can my DADU sit?
Five feet from side and rear lines — but only if it's a stand-alone DADU. Combine it with a garage or other structure and standard setbacks apply, so the configuration choice matters.
SMC 21.04.030.C conditions (4), (7) · Permalink
The rules at a glance
| ADUs allowed per lot | Two ADUs per lot with a single-family home — two attached, two detached (in one or two structures), one of each, or conversions of existing structures like a detached garage.SMC 21.05.010.C(5)(a)(i)–(ii) |
| Maximum size | 1,000 sq ft; an ADU entirely within the existing residence may be the larger of 50% of the home's floor area or 1,000 sq ft.SMC 21.05.010.C(5)(a)(iii) |
| Detached ADU height | 24 ft for detached ADUs in every residential zone (the primary residence gets 35 ft in R-1 through R-8, 60 ft in R-12/R-18).SMC 21.04.030.C height table |
| Detached ADU setbacks | Side 5 ft and rear 5 ft in every residential zone — but only for stand-alone DADUs; a DADU combined with another structure (garage, pool house) takes standard structure setbacks. Accessory-structure front setbacks run 10–20 ft by zone (30 ft on arterials).SMC 21.04.030.C + conditions (4), (7) |
| Off-street parking | No additional space required when the parcel already has four or more; and no minimum parking at all for homes, ADUs, and middle housing within a quarter mile of an existing or planned transit stop — counting planned stops is unusually generous.SMC 21.05.010.C(5)(a)(iv); 21.06.030 |
| Owner-occupancy | None — no owner-occupancy condition appears anywhere in the adopted ADU regulations.SMC 21.05.010.C(5)(a) (verified absence) |
| Lot coverage / floor area | ADUs are exempt from FAR and hardscape-coverage calculations on single-family lots — a significant design lever. The 3,000 sq ft per-building footprint cap still applies, and the two ADUs together count as one dwelling unit for density.SMC 21.04.030.C ('Exempt' row) + condition (10); 21.05.010.C(5)(a)(v) |
| Permit path & timeline | Building permit via MyBuildingPermit.com. No published review timeline (secondary sources suggest roughly 8–14 weeks for single-family-class review).City Permit Center page |
Worth knowing
- The FAR/hardscape exemption is the standout: on Sammamish's large-home lots, an ADU doesn't eat the main house's floor-area budget — the reverse of Seattle's 2026 change.
- The 'planned transit stop' parking waiver means lots near future transit corridors already qualify.
- The city's inclusionary fee-in-lieu ($34.45/sq ft, enacted March 2025) exempts projects of 1,500 sq ft or less, and ADUs up to 1,000 sq ft are excluded from the affordable-housing calculation.
- The city's DADU handout No. 310 (Sept 2023) is dangerously stale — 18-ft height, one DADU, two parking spaces, façade-matching — none of it current.
- No pre-approved ADU plan program.
On our watchlist
The SMC is current through Ordinance O2026-595 (May 2026); whether any 2025–26 ordinance touched the ADU sections is unverified because the code host blocks automated access — no ADU changes surfaced in searches. We re-check each pass.
The 'two ADUs count as one dwelling unit' density phrasing is loose — worth confirming the city's interpretation if density is load-bearing for a project.
Check your parcel
The rules above are citywide — what you can build depends on your lot’s zone, size, and setbacks. Look yours up on the official viewers:
- King County Parcel Viewer
- King County Assessor Property Search (eRealProperty)
- Sammamish Property Tool (zoning & parcels)
Primary sources
- Adopted 2024 Comp Plan code updates (Ord O2024-578)
- City ADU page
- DADU handout 310 (stale — for contrast)
Other Washington cities
Bellevue · Bothell · Burien · Edmonds · Everett · Issaquah · Kent · Kirkland · Lynnwood · Olympia · Redmond · Renton · Seattle · Shoreline · Tacoma
Not legal advice. Every fact above cites the code section it comes from — check the cite, or ask your city’s planning department to confirm your specific lot. Spotted an error or a new ordinance? See about to reach us; corrections are logged in the changelog.