Guide · Sammamish · King County · Updated July 2026
How many units can you build in Sammamish?
If you own or are evaluating a residential lot in Sammamish, the first question is almost always the same: how many homes can legally go on it? Since Washington's HB 1110 middle-housing law took effect, the answer for most Sammamish lots is now more than one. Sammamish allows 3 units per lot by right, rising to 4 with an affordable unit, a retained home, or transit proximity, and up to 6 per structure via net-density rules.
Sammamish at a glance: 3 units per lot by right, up to 6 with the city's bonus, plus up to 2 ADUs under HB 1337. Source: SMC 21.04.030 & the MHO overlay (Ord. O2024-578).
What Sammamish's adopted code allows
Sammamish allows 3 units per lot by right, rising to 4 with an affordable unit, a retained home, or transit proximity, and up to 6 per structure via net-density rules. ADUs count toward the maximum.
The details: 4 with an affordable unit, a retained existing home, or transit proximity; up to 6 per structure via net-density rules. These are Sammamish's city-wide standards, per SMC 21.04.030 & the MHO overlay (Ord. O2024-578); the exact figure for a specific parcel — its zone, lot size, transit proximity, and critical areas — is what a Civexa report resolves.
What actually fits: floor area, height, and setbacks
HB 1110 and the city code set the right to a number of units; the zone's building envelope sets what physically fits. Floor-area ratio, lot coverage, height, and setbacks together decide whether those homes pencil as detached cottages, a townhouse row, or a stacked-flat building. Civexa computes this envelope for Sammamish zone by zone, so the unit count you see is one the zoning can actually hold.
What can shrink it: critical areas
Steep slopes, wetlands, streams, and flood zones can override the unit math on a specific parcel. A lot that qualifies for the maximum on paper may be constrained once environmentally critical areas are mapped. Civexa screens FEMA flood, slope, and county critical-area layers for every Sammamish address so you find this out before you make an offer, not after.
Get the exact number for your Sammamish parcel
The figures above are Sammamish's city-wide rules. The number that matters is the one for your address — its zone, lot size, transit proximity, and critical areas. Civexa turns that into a full feasibility report in about a minute: unit count, buildable envelope, a preliminary pro forma, utilities, and permit path.
Run a Sammamish feasibility report →
Frequently asked
How many units can I build on a residential lot in Sammamish?
Sammamish allows 3 units per lot by right, rising to 4 with an affordable unit, a retained home, or transit proximity, and up to 6 per structure via net-density rules. That is per SMC 21.04.030 & the MHO overlay (Ord. O2024-578). The exact number for a specific parcel still depends on its zone, lot size, transit proximity, and critical areas — run a Civexa report for the parcel-level figure.
Can I add ADUs on top of that in Sammamish?
Washington's HB 1337 allows up to two accessory dwelling units on a residential lot. In some cities they count toward the middle-housing total and in others they are separate — your Civexa report applies Sammamish's specific rule.
What unlocks the maximum in Sammamish?
4 with an affordable unit, a retained existing home, or transit proximity; up to 6 per structure via net-density rules.