Guide · Mountlake Terrace · Snohomish County · Updated July 2026
How many units can you build in Mountlake Terrace?
If you own or are evaluating a residential lot in Mountlake Terrace, 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 Mountlake Terrace lots is now more than one. Mountlake Terrace permits 2 to 6+ units per lot depending on the residential district, with sixplexes unlocked through its affordability incentive.
Mountlake Terrace at a glance: 2 units per lot by right, up to 6 with the city's bonus, plus up to 2 ADUs under HB 1337. Source: MTMC 19.30 Table 19.30.030 (Ord. 2884).
What Mountlake Terrace's adopted code allows
Mountlake Terrace permits 2 to 6+ units per lot depending on the residential district, with sixplexes unlocked through its affordability incentive. R-1 is the 2-unit floor; R-4 has no flat unit cap.
The details: varies by district — R-2 reaches a sixplex via the affordability bonus, R-3 permits all middle-housing types through sixplexes, and R-4 adds multifamily with no flat cap; no transit tier. These are Mountlake Terrace's city-wide standards, per MTMC 19.30 Table 19.30.030 (Ord. 2884); 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 Mountlake Terrace 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 Mountlake Terrace address so you find this out before you make an offer, not after.
Get the exact number for your Mountlake Terrace parcel
The figures above are Mountlake Terrace'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 Mountlake Terrace feasibility report →
Frequently asked
How many units can I build on a residential lot in Mountlake Terrace?
Mountlake Terrace permits 2 to 6+ units per lot depending on the residential district, with sixplexes unlocked through its affordability incentive. That is per MTMC 19.30 Table 19.30.030 (Ord. 2884). 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 Mountlake Terrace?
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 Mountlake Terrace's specific rule.
What unlocks the maximum in Mountlake Terrace?
Varies by district — R-2 reaches a sixplex via the affordability bonus, R-3 permits all middle-housing types through sixplexes, and R-4 adds multifamily with no flat cap; no transit tier.