Possible, but hard and costly. The ground is steep, with slopes averaging about 38%. That raises the cost of a driveway, septic, and foundation. The growing season runs about 279 frost-free days, long enough for a spring and a fall garden. The U.S. Forest Service rates wildfire risk high across much of the county, so plan cleared ground around the house.
What the land says
Rain
Rain helps, but plan on a well for most of your water and on watering the garden in dry months.
About 34 inches a year (PRISM, 1991 to 2020 average)
Wells
Typical well depth. Budget for a mid-range well.
The typical well here is about 170 feet deep; a well typically runs $10,000 to $22,000
Growing season
Long enough for a spring and a fall garden.
About 279 frost-free days, USDA zone 9b; last frost about March 2, first about December 5
Sun
Strong sun. A modest solar array covers a household.
About 5.9 hours of full sun a day, averaged over the year
Flood
Flood zones run along creeks and rivers here. Look up the parcel on FEMA's flood map.
FEMA maps flood zones within a quarter mile in places
Wildfire
Wildfire risk is high across much of the county. Plan cleared ground around the house and fire-resistant materials.
U.S. Forest Service wildfire hazard map: Low to High here
Storms
Hurricanes and strong tornadoes are rare here.
NOAA: no hurricane-strength storm within 50 miles since 1975; no strong (EF2 or stronger) tornado within 25 miles since 1990
Earthquakes
Strong shaking is possible. Build to the seismic code and brace the water tank.
USGS seismic hazard map: very high
Terrain
Steep. A flat house site and a driveway route will drive the cost.
Slopes average about 38%, about 890 feet above sea level
Soil
Expect a costlier septic system, because rock or a hard layer sits about 30 inches down. The county's soil test decides.
Loam, well drained (USDA soil survey). A mound, sand filter, or treatment unit typically runs $10,000 to $20,000
Road
Paved roads are close by.
Nearest paved road usually within about 0.9 miles (OpenStreetMap)
Check a California parcel, or plan the one you own
Get a free 0-100 off-grid score.
A step-by-step build plan, sizing your solar, water, garden, septic, heat, and buildings.
Is it legal here?
Zoning
Napa County zones land outside its towns and publishes its zoning map. Our free lookup shows the district for any address.
Building code
The California Building Standards Code (Title 24) applies statewide and every city and county must enforce it, so a new house needs a permit however remote. A county may adopt the state's optional rules for owner-built rural homes, which relax some standards but still require a permit.
Rainwater
Collecting it is allowed.
Composting toilets
Allowed with a permit and an approved unit.
Water rights
A mix of two systems. Ask the state water office before you drill a well or dam a creek.
Drilled to about 170 feet, with pump and pressure tank
Septic
$10,000 to $20,000
Mound, sand filter, or treatment unit
Solar and batteries
$18,000 to $32,000
Sized for a modest household
Road or driveway
$4,000 to $10,000
From the nearest road to a house site
Clearing
$1,000 to $5,000
A house site, solar, and garden
Total
$42,000 to $88,000
Before the house
Before you make an offer on land here
Soil test
Get a soil test before you count on septic.
Rock or a hard layer sits about 30 inches down, which can rule out a standard system.
Wildfire
Ask an insurance agent whether they will write a policy.
The U.S. Forest Service rates wildfire risk high across much of the county.
Flood map
Look up the parcel on FEMA's flood map.
Flood zones run along creeks and rivers here. Building in one means flood insurance and extra permits.
Nearby counties
133,216 people live in Napa County, about 177.2 per square mile. It ranks tied for 45th of the 58 California counties we scored, and California ranks 45th of 50 states.