ADU Rules in Lake Stevens, WA: Size, Number and Parking (2026)
By Eric Dexter, Owner & Builder ·
Lake Stevens is a few minutes from our Monroe base, and it has its own ADU code, separate from both Snohomish County's and Seattle's. The City updated its rules to match Washington's ADU law, and they now read cleanly. Here is what Lake Stevens allows in 2026, from the City's current ADU handout and submittal checklist.
The short version
- Two ADUs per lot, under Lake Stevens Municipal Code 14.44.045 — two detached, two attached, or one of each.
- 250 to 1,000 sq ft of gross floor area per ADU, per the City's 2026 submittal checklist.
- A larger unit can be allowed when it sits entirely on one floor inside the footprint of the main house or an existing legal accessory structure — a basement or a converted outbuilding, say.
- Zone standards apply for height, setbacks and impervious surface, the same as for the main house.
- One parking space per ADU, in addition to the main house's parking, per the City's handout.
How that fits state law
Washington's 2023 ADU law requires cities inside urban growth areas to allow two ADUs per lot, prohibits caps smaller than 1,000 sq ft, and bars ADU-specific dimensional rules stricter than those for the main house. Lake Stevens' code sits right at that statutory floor. The state also limits parking requirements within half a mile of a major transit stop, which does not reach most Lake Stevens lots, so the one-space rule generally applies. Background in Washington's ADU laws.
What usually decides a Lake Stevens project
- Impervious surface. The unit, its parking space and the path to it all add hard surface, and the zone's impervious limit can bind before the size cap does.
- The parking space itself. On a narrow lot, finding a legal space that doesn't block the house's parking shapes the whole site plan.
- Lakefront and critical areas. Shoreline jurisdiction, wetlands, streams and steep slopes bring their own review and buffers. Lots near the lake deserve an early check — see building on a difficult lot.
- Sewer or septic. Most in-city lots are sewered; anything on a septic system goes through the Snohomish County Health Department first — ADUs on septic.
Inside the city or outside it?
A Lake Stevens mailing address does not mean the City governs the lot. Unincorporated parcels around the city go through Snohomish County Planning and Development Services under the County's code, and rural parcels outside the urban growth area fall under a different framework again — Washington's rural DADU law. The parcel lookup in how to check your zoning settles it in a few minutes.
Building one in Lake Stevens
Two 1,000 sq ft units on one lot is a lot of house, and most owners build one first. Our 1,000 sq ft two-bedroom plans are sized for exactly this cap, and ADU floor plans by size shows what fits below it. Rules and handouts change, so confirm the current version with the City's planning department before design. Or send us the address — we will confirm the jurisdiction, the parking and the impervious budget, and tell you what the lot can carry. More on our Lake Stevens page.
