Guide · Mill Creek · Snohomish County · Updated July 2026
How many units can you build in Mill Creek?
If you own or are evaluating a residential lot in Mill Creek, 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 Mill Creek lots is now more than one. Mill Creek allows at least 2 units per lot in its Neighborhood Residential zone, with middle-housing types up to sixplexes permitted subject to a density cap.
Mill Creek at a glance: at least 2 units per lot, with more allowed by lot size and zoned density, plus up to 2 ADUs under HB 1337. Source: MCMC Ch. 17.02/17.04 (Ord. 2025-933).
What Mill Creek's adopted code allows
Mill Creek allows at least 2 units per lot in its Neighborhood Residential zone, with middle-housing types up to sixplexes permitted subject to a density cap.
The details: no transit tier (Tier 3); middle-housing types up to sixplexes are permitted, capped by density (about 6 homes per acre). These are Mill Creek's city-wide standards, per MCMC Ch. 17.02/17.04 (Ord. 2025-933); 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 Mill Creek 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 Mill Creek address so you find this out before you make an offer, not after.
Get the exact number for your Mill Creek parcel
The figures above are Mill Creek'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 Mill Creek feasibility report →
Frequently asked
How many units can I build on a residential lot in Mill Creek?
Mill Creek allows at least 2 units per lot in its Neighborhood Residential zone, with middle-housing types up to sixplexes permitted subject to a density cap. That is per MCMC Ch. 17.02/17.04 (Ord. 2025-933). 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 Mill Creek?
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 Mill Creek's specific rule.
What unlocks the maximum in Mill Creek?
No transit tier (Tier 3); middle-housing types up to sixplexes are permitted, capped by density (about 6 homes per acre).