Can I build a backyard home in Sammamish?
Since 2023, Washington law lets most city lots hold up to two more homes. Sammamish writes its own rules on top. Here’s what the code says, in plain English — and a free report on what may fit on your lot.
What Sammamish allows.
The headline standards. Tap any one for the full wording and the code section.
ADUs per lot2: two attached, two detachedFull wording
2: two attached, two detached (in one or two structures), or one attached plus one detached, per lot with one single-family detached residence; conversions of existing structures such as a detached garage are allowed (SMC 21.05.010.C.5.a.i, iv).
Max size1,000 sq ft (more for a unit inside the house)Full wording
1,000 sq ft floor area per ADU. If an ADU is wholly inside the existing house, the cap is 50% of the existing unit's floor area or 1,000 sq ft, whichever is larger (SMC 21.05.010.C.5.a.v).
Max height24 ft for detached accessory dwellings in every residential zoneFull wording
24 ft for detached accessory dwellings in every residential zone (SMC 21.04.030.C table).
Front setbackNo DADU-specific front setbackFull wording
No DADU-specific front setback, so the zone front setback applies. In R-4/R-6 it is 15 ft for buildings under 2,500 sq ft (20 ft for a garage) (SMC 21.04.030.C; city Handout 130, Mar 2025).
Side setback5 ft for a stand-alone detached ADU in all residential zonesFull wording
5 ft for a stand-alone detached ADU in all residential zones (SMC 21.04.030.C, notes 4 and 7). Standard setbacks apply when the DADU is combined with another structure (note 7).
Rear setback5 ft for a stand-alone detached ADU in all residential zonesFull wording
5 ft for a stand-alone detached ADU in all residential zones (SMC 21.04.030.C, notes 4 and 7). The code table has no alley lot-line rule; RCW 36.70A.681 alley siting applies.
Lot coverageR-4: 40% maximum hardscape coverageFull wording
R-4: 40% maximum hardscape coverage (R-6 50%, R-1 30%). ADUs are exempt from hardscape and FAR calculations (SMC 21.04.030.C, note 10).
ParkingNot confirmed yet — none extra if the lot has 4+ spacesFull wording
Not confirmed yet — ask the city. The code says no additional off-street space is required when the parcel already has four or more parking spaces (SMC 21.05.010.C.5.a.ix). The base per-ADU requirement was not found.
Where a city figure reads stricter than the state floor (RCW 36.70A.681), the floor may control — the report flags it for your parcel.
Living there, selling it, plans, time and fees.
Each answer is the code’s own wording, with the section it comes from. “Not published yet” means the city hasn’t posted a figure — the report asks the city, not the internet.
Are backyard homes allowed?
Yes. Residential accessory uses, including ADUs, are permitted (P5) in the R-1 through R-8 and R-12 through R-18 zones and not in NB, CB or O (SMC 21.05.010 use table, condition 5.a). Two detached ADUs are an allowed configuration (SMC 21.05.010.C.5.a.iv).
Minimum lot size
None for an ADU in SMC 21.05.010.C.5.a; the zone minimum applies to new lots.
Do you have to live there?
No. Current SMC 21.05.010.C.5.a contains no owner-occupancy condition; several former ADU conditions were repealed by Ord. O2024-578.
Can it be sold on its own?
Not addressed; RCW 36.70A.681 floor applies
Pre-approved plans
None found
How long the city takes
Not published
Impact fees
Not found; RCW 36.70A.681 caps ADU impact fees at 50% of the principal unit's
Plans Sammamish has already approved.
A pre-approved plan skips the design review: Sammamish has already checked the drawings, so the permit review is about your lot.
Loading the plans…
Pictures are the official pages’ own. A pre-approved plan is not a permit: the city still reviews your site.
The code is half the answer. Your parcel is the other half.
Lines and easements
Where the lot lines really are, which setbacks apply on each side, and whether a utility or access easement takes the corner you had in mind.
Critical areas and slope
Steep slopes, wetlands and streams come with buffers that no citywide number shows. The report reads the county’s maps for your parcel.
Sewer, septic, water, trees
Whether sewer reaches the lot or it’s on septic, where the water service is, and which trees a city protects — the things that decide where a unit can actually go.
What Sammamish allows, what could fit on your lot, and a planning cost range. If something won’t fit, the report says so — and shows what might.
Where this page comes from.
Read from the Sammamish municipal code and the city’s own pages on November 5, 2026. The same table feeds the HousUp report, so the report and this page never disagree. Cities amend their codes; before you design anything, confirm the current wording with the city.
2 sources, read November 5, 2026
Find out what your property could become.
Type your address. Within a few hours: what Sammamish allows, what could fit, and a planning cost range. Free, no obligation.