Off-grid site report
Napa County, CA
38.2971, -122.2855 · 20 ft elevationRead this before you act on anything below. This is my researched starting point for Napa County, CA, not legal advice and not a guarantee. Rules change, and the deciding facts on any specific parcel (setbacks, perc results, overlay districts, deed restrictions, road frontage) live at the county or town office, not in any database. Before you buy land or build, confirm the current rules directly with the local zoning and health offices - the sources on this page tell you exactly who to call.
The local rulesNapa County, CA
Zoning & raw-land occupancy
RestrictedNapa County has countywide zoning (Title 18), so there's no unzoned raw land to simply occupy. Most rural parcels sit in Agricultural Preserve or Agricultural Watershed districts geared toward farming, and residential use has to tie to an approved dwelling and the allowed-uses list for that district, per Napa County Planning, Building & Environmental Services (PBES). source
Dwellings, tiny homes & RVs
RestrictedManufactured homes on permanent foundations are only allowed in specific zoning districts (AW, AP, RS, PD) and need a building permit, while factory-built and kit homes must meet the California Building Code and are inspected by the county. Napa County has not adopted a tiny-home-on-wheels ordinance like some neighboring counties, so using an RV or THOW as a primary residence isn't confirmed as a legal pathway, per Napa County PBES Building Division. source
Building permits & codes
RestrictedAny new or replacement dwelling, including manufactured home installs and kit/factory-built homes, needs a Napa County building permit, and that approval is contingent on first satisfying both water-supply and wastewater-disposal requirements, per PBES Building Division working with Environmental Health. source
Septic & composting toilets
RestrictedNapa County's Environmental Health Division (Well and Onsite Wastewater Treatment) requires a site evaluation, a permitted design, and a sewage permit application before any septic/OWTS installation, with setbacks set by County Code Chapter 13.28/13.32. Whether composting toilets can substitute for a permitted system is not confirmed, so ask this office directly. source
Greywater reuse
Unclear - verifyI couldn't find a Napa County-specific greywater ordinance in official sources; it appears the county just administers the state's California Plumbing Code Chapter 15 baseline through Building/Environmental Health permitting. Confirm any local nuance directly with Napa County PBES.
Rainwater harvesting
Unclear - verifyNo Napa County ordinance specifically addressing rooftop rainwater harvesting beyond the state's Rainwater Capture Act baseline turned up in official sources, so it looks like the state standard applies, but this isn't confirmed with a distinct county rule.
Private wells & water rights
RestrictedNapa County's Well and Onsite Wastewater Treatment division issues its own well construction permits and, in designated groundwater-deficient basins, requires a separate groundwater permit (a ministerial groundwater permit option exists for new single-family homes on parcels over 2 acres). A yield test within the past five years is also required before a building permit can be approved, per Napa County Code Chapter 13.12/13.15. source
Living disconnected from utilities
Unclear - verifyNo official Napa County source directly addresses living fully disconnected from utilities as its own legal category. In practice, the county's building permit process effectively requires a permitted well and septic system before a dwelling gets approved, so a truly off-grid, unpermitted setup isn't a recognized legal path; confirm specifics with PBES Building and Environmental Health. source
Sun30-year normals
- Peak-sun hours, annual average
- 5.8 hrs/day
- Worst month (sizes an off-grid array)
- 3.4 hrs/day
- Yearly output per 1 kW of panels
- 1,602 kWh
JFMAMJJASOND
Weather1991-2020
- Precipitation
- 28 in/yr
- Heating degree days
- 2,511 (mild)
- Frost-free season
- Feb 11 to Dec 5
How far help isstraight-line
- Hospital
VacaValley Hospital - 18.6 mi
- Fire station
Carneros. Vol. Fire Dept Satelite Station 210 - 3.8 mi
- Hardware store
Friedman's - 9.5 mi
- Grocery
Grocery Outlet - 1.2 mi
From OpenStreetMap. Road miles will be longer, often much longer in hill country.
Plan this spot
These open with this location's real numbers already filled in (ZIP 94581).
Size a solar systemHeat loss & insulationFirewood per winterRainwater harvestGarden sizePanel tilt
Looking at a specific parcel in Napa County, CA?The rules above are the jurisdiction. The land check runs the parcel itself: flood zone, soils and septic suitability, wetlands, slope, access, climate, and these verdicts, from a parcel number or coordinates.
Check a parcel →Share or save this report:New report
Sources: US Census Bureau geocoder; NLR PVWatts v8 (solar); NOAA NCEI 1991-2020 climate normals (nearest station) or Open-Meteo (ZIP-centroid) for weather; Open-Elevation; OpenStreetMap contributors. Public data retrieved Aug 22, 2026; agencies update their layers on their own schedules. Planning data, not a survey or legal advice.
New here, or not sure where this fits? Start here walks through the whole thing in order.