Off-grid site report
San Mateo County, CA
37.4789, -122.1462 · 10 ft elevationRead this before you act on anything below. This is my researched starting point for San Mateo 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 rulesSan Mateo County, CA
Zoning & raw-land occupancy
Varies locallyIn unincorporated San Mateo County, zoning is set by the County Planning Department under the newly reorganized Development Code (Title 8), with rural, agricultural, and Coastal Zone districts carrying extra hazard and resource standards. Incorporated cities and towns like Woodside, Portola Valley, and Half Moon Bay set their own zoning, so you have to check with the specific jurisdiction where your land sits. source
Dwellings, tiny homes & RVs
RestrictedThe County has definitions for RVs and manufactured/mobile homes (mirroring state Health & Safety Code) but treats them as park-sited housing types, not a general right to live full-time on raw land in an RV or tiny home. Long-term occupancy outside a licensed park runs into zoning use-permit and building code enforcement, so I'd confirm with County Planning before counting on it.
Building permits & codes
RestrictedThe County's Title 10 (Building Regulations) governs permitting in unincorporated areas, and Design Review, Coastal Zone, Resource Management, and Planned Agriculture districts always require planning review before you even get to building permits. Towns like Woodside add their own municipal building and site development permits on top of the County's process. source
Septic & composting toilets
RestrictedSan Mateo County Environmental Health Services says septic is the only approved on-site wastewater system where there's no sewer, and alternative systems (composting, holding tanks) need a separate County operating permit with heightened oversight. Woodside and likely other towns require a dual permit from both the town and County EHS for any new, expanded, or repaired septic system. source
Greywater reuse
Generally allowedA simple clothes-washer-to-mulch-basin or sub-surface irrigation system that meets the Uniform Plumbing Code standard doesn't need a permit from Environmental Health, but any larger or building-connected greywater system does require plans submitted to EHS and possibly the local building department. Reuse of actual blackwater/sewage can only be permitted by the State. source
Rainwater harvesting
Generally allowedSimple rain barrels not tied into your home's plumbing don't need a County permit, but larger or plumbing-connected systems go through the same Environmental Health 'Alternative Water' review as greywater. The County also actively promotes harvesting through its Green Infrastructure program, and some cities like San Mateo even offer rebates. source
Private wells & water rights
RestrictedEnvironmental Health Services issues well construction and destruction permits under County groundwater standards, and a special local ordinance adds extra requirements for wells in the Westside Basin Aquifer area north of Highway 92 and west of Highway 280. If you're in the Coastal Zone you'll also need a Coastal Development Permit from Planning, and towns like Woodside layer on their own building permit requirements too. source
Living disconnected from utilities
Unclear - verifyI couldn't find any County ordinance that directly addresses living off the electric or water grid as its own legal category, so this is not confirmed. In practice it comes down to whether your dwelling can satisfy the building code, zoning, and Environmental Health requirements for an approved sewage system and water supply, so it's worth asking County Planning and Environmental Health Services directly about your specific setup.
Sun30-year normals
- Peak-sun hours, annual average
- 5.8 hrs/day
- Worst month (sizes an off-grid array)
- 3.7 hrs/day
- Yearly output per 1 kW of panels
- 1,646 kWh
JFMAMJJASOND
Weather1991-2020
- Precipitation
- 16 in/yr
- Snowfall
- 0 in/yr
- Heating degree days
- 2,732 (mild)
- Frost-free season
- Feb 7 to Dec 6
How far help isstraight-line
- Hospital
Menlo Park Surgical Hospital - 1.4 mi
- Fire station
Menlo Park Fire District Station 2 - 0.8 mi
- Hardware store
Yardbird Equipment - 5.0 mi
- Grocery
Mercadito Latino - 4.3 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 94303).
Size a solar systemHeat loss & insulationFirewood per winterRainwater harvestGarden sizePanel tilt
Looking at a specific parcel in San Mateo 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.