Off-Grid Living in King County, Washington

I'm looking at unincorporated King County here, not Seattle, Bellevue, Renton, or any of the other incorporated cities inside the county, since those all run their own zoning and building codes that override the county rules once you cross into city limits. If your parcel sits inside a city, start with that city's planning department instead.

Zoning. King County zones unincorporated land countywide under Title 21A of the King County Code, run by the King County Council/Department of Local Services. You'll land in something like Rural Area, Agricultural, Forestry, Mining, or a rural town zone, and each has its own permitted-use table and setbacks (Rural Area zones, for instance, carry a 30-foot front setback). Raw land isn't a blank slate, so pull your parcel's zoning from the county GIS lookup before planning anything.

Dwellings, tiny homes, RVs. The county requires any dwelling unit, tiny home included, to have an approved potable water source and wastewater system, which in rural areas usually means a permitted well and septic. RVs are for temporary camping only, capped at 60 days in a rolling year, and you can't just park and store one on vacant land. ADUs are allowed on most lots (one per primary house) but not in Forest-zoned parcels. Tiny houses on foundations follow the state building code; tiny houses on wheels get treated like RVs.

Building permits. The county's Department of Local Services Permitting Division enforces the state building code locally, cross-checked against Title 21A's density and dimension tables.

Septic and composting toilets. Public Health - Seattle & King County runs on-site sewage system permitting under Board of Health Code Title 13, which adopts the state's WAC 246-272A rules and applies stricter county provisions where they exist. The county updated its OSS rules in 2025, and Public Health is currently warning of longer-than-usual review times due to a system transition and staffing. Composting toilets need to be on the state DOH's registered products list and installed under a county permit.

Greywater. I couldn't confirm a King County-specific greywater ordinance; the state's WAC 246-274 framework, applied by local health jurisdictions, presumably fills the gap, but treat this as unconfirmed and ask Public Health directly.

Rainwater. No county restriction turned up in my research; this looks like it follows Washington Department of Ecology's generally permissive state stance, but I haven't found a county-specific page confirming it.

Wells. Permit-exempt wells are allowed, but King County Public Health caps domestic exempt wells at 950 gallons/day per residence with limited irrigation, and any system serving two or more parcels needs Group B public water system permitting. Some rural subdivisions require a recorded covenant for future Group A connection.

Off-grid utilities generally. No blanket ban, but since occupancy permits hinge on an approved water and septic system, full disconnection from water/sewer infrastructure is functionally gated by that permitting process rather than outlawed outright.