How do I find out if my lot is zoned for an ADU?

Look the address up in the mapping tool for the jurisdiction that governs it: Seattle’s SDCI online GIS property map inside city limits, King County’s parcel viewer for unincorporated King County, and Snohomish County’s online property information map for unincorporated Snohomish County. Other cities have their own maps. Note the zone, the lot area and whether any critical-area or urban-growth-area layer touches the parcel.

What is the difference between city and county zoning for an ADU?

If the address is inside a city’s limits, that city’s code and permit office govern the ADU. If it is unincorporated, the county does. The rules, size limits and fees differ between them, and outside an urban growth area a different state framework applies entirely.

Do I need a survey before checking zoning?

No. Public maps give the zone, approximate lot lines and dimensions, which is enough to know whether an ADU is plausible. A survey comes later, once feasibility has confirmed it is worth designing.

The DIGS Journal

Permitting & Process6 min read

How to Check Your Zoning Before an ADU: Seattle, King County and Snohomish County

By Eric Dexter, Owner & Builder · October 25, 2026

Excavation for a DIGS Construction DADU on a Seattle lot — the result of checking zoning and site constraints first

Before any builder draws anything, five facts about your parcel decide whether an ADU is possible and roughly what it will cost: which jurisdiction governs it, what zone it is in, how big the lot is, whether a critical area touches it, and whether it sits inside or outside the urban growth area. All five are public, free, and findable in about ten minutes. Doing this homework before the first call turns a generic conversation into a specific one.

Step 1: find out who governs the lot

The mailing address lies. A “Bothell” or “Snohomish” or even “Seattle” postal address can be inside city limits, in an unincorporated pocket governed by the county, or in a neighboring city entirely. The jurisdiction decides which ADU code applies, which counter reviews the permit, and what it costs — the differences are large, as ADU rules in Snohomish and King County shows. The county assessor's parcel record is the quickest way to settle it: it lists the taxing district and jurisdiction for every parcel.

Step 2: the map tools, by jurisdiction

Seattle. The Seattle Department of Construction and Inspections (SDCI) publishes an online GIS property map. Search the address and you get the zone (for most houses, one of the Neighborhood Residential zones), lot dimensions, environmentally critical area overlays, and permit history. The old printed zoning map books were retired in 2025; the online map is now the source.
Unincorporated King County. The County's online parcel viewer shows the parcel outline, zoning, the urban growth boundary and critical-area layers. Cities inside King County — Bellevue, Kirkland, Redmond, Shoreline and the rest — each publish their own zoning map and ADU page; see ADU rules on the Eastside.
Unincorporated Snohomish County. The County's online property information map does the same job: zoning, parcel size, critical areas, and crucially the UGA line. Everett, Lynnwood, Monroe and the City of Snohomish have their own maps for addresses inside their limits.

Tool names and web addresses change; the search that reliably finds the current one is the jurisdiction's name plus “zoning map” or “parcel viewer.” Use the official .gov result, not a third-party aggregator — those are often years out of date.

Step 3: write down these five things

Zone. The code, exactly as written (NR2, R-6, R-5, LR1 and so on). It sets lot coverage, height and how many units the lot can hold — how big a DADU can be explains what the Seattle zones allow.
Lot area and dimensions. Square footage, and the width and depth. Lot coverage is a percentage of area, so this number sets the ceiling on everything.
Critical-area layers. Steep slope, landslide or liquefaction hazard, wetland, stream buffer, flood zone. Any of these changes the project; some end it. See building on a difficult lot.
UGA status. Inside the urban growth area the state ADU mandate applies. Outside it, a different framework does — Washington's rural DADU law. On county maps this is a single on/off layer.
Sewer or septic. Most county maps show sewer service areas; the assessor record or a septic as-built shows whether the house is on a system. It decides the bedroom count — ADUs on septic.

What the maps cannot tell you

Public maps are a screening tool, not an answer. They do not show recorded covenants or HOA rules, which a permit does not override; they do not show tree protection on individual trees, soils, groundwater, or whether the existing electrical service has capacity; and parcel lines on a GIS map are approximate, not surveyed. That is the gap a feasibility study closes, and why it comes before design. But a homeowner who arrives with the zone, the lot size and the overlays already written down has done the first third of that study for free.

Bring it to the first call

Those five facts are the most useful thing you can hand a builder at a first consultation — more useful than a Pinterest board. What that consultation covers is in what happens at a free ADU consultation. If you would rather we pull the records, send us the address and we will tell you what the maps say and what they are hiding.