Off-Grid Living in San Francisco County, California

Planning a build in San Francisco County

The rules above decide what you may build. The numbers below decide what you will have to build, and they come from this place rather than from a national average.

Solar: size for the worst month, not the average

San Francisco County averages 5.3 peak sun hours a day across the year, but its worst month averages 3.7. That is a drop of about 31 percent. An array sized on the annual figure will therefore come up short in the worst month by roughly that much, in the season when lights, pumps, and heating fans all run hardest.

Put another way, meeting the same daily load in the worst month here takes about 1.4 times the array that the annual average implies, or a generator and the fuel budget to run it. Neither is wrong; what is wrong is discovering the gap in the first winter. The solar calculator runs this arithmetic against your own load list, and lesson four covers building that list before buying panels.

Heat: 2,909 heating degree days

That is a moderate heating season, where a single well-chosen appliance usually carries the house. Heating demand at this level dwarfs everything electrical in the house, which is why almost nobody here heats with electricity from a battery bank.

As a rough order of magnitude, a small, reasonably insulated cabin heated mainly with wood in a climate like this tends to burn in the region of 2.4 cords a season, with the real figure swinging widely on insulation, house size, and how you burn. Treat that as a bracket for planning your woodshed rather than a promise, split and stack a season ahead, and check with a moisture meter before burning. The firewood calculator and heat-loss calculator narrow it down from your own building.

Water: what the roof would actually catch

San Francisco County receives about 23.7 inches of precipitation a year. A 1,000 square foot roof here would shed on the order of 12,524 gallons a year at a realistic 85 percent collection efficiency, before any losses to first-flush diversion, evaporation, or overflow in a heavy storm.

The annual total is the easy part. What sizes a cistern is the longest dry stretch, because catchment is seasonal almost everywhere and a tank that covers the average year can still run empty in August. Check the local rules too: rainwater harvesting is regulated in some states even where it is broadly allowed. The rainwater calculator works from your own roof and rainfall pattern, and lesson three covers why water is chosen before power.

Distance is part of the plan

Measured straight line from the center of San Francisco County: the nearest fire station is about 7.0 miles away (Muir Beach Volunteer Fire Deparment), the nearest hospital is about 29.0 miles away (Menlo Park Surgical Hospital), the nearest supermarket is about 2.3 miles away (Calmart). Road miles will be longer, and in winter longer again.

The fire distance is worth noting before you buy rather than at renewal: insurers commonly rate rural property partly on how far it is from a responding station and from a water source, and some decline off-grid or owner-built structures outright. Ask an agent who writes rural policies what they would need to see, while the answer can still change what you build. Lesson eleven covers the insurance and financing side.

The hospital distance sets what your first aid kit and your medical plan have to cover in the gap, and it is the number to think about before anyone in the household depends on refrigerated medication or mains-powered equipment.

Confirming this for your own parcel

On this page 1 of the eight topics is recorded as unclear or as varying within San Francisco County: mandatory utility connection. Those are the calls to make first, because they are the ones where a general answer cannot be trusted for a specific parcel. Ask for the answer in writing where the office will give it, and note the name and the date where it will not.

Where a topic is recorded as settled here (zoning, what counts as a dwelling, building permits and codes, septic and sewage, greywater, rainwater harvesting, wells and water rights), the source is cited further down this page. Sources go stale, ordinances get amended, and this site logs corrections publicly rather than editing them away, so if you find something here that no longer matches the county, the corrections page is how to say so.

Before any of those calls, walk the parcel with the land walk checklist and take the questions for the county with you. The parcel check pulls flood, wetland, slope, and access data for a specific parcel and shows its sources, which is a good way to arrive at the office with the questions already framed. Lesson two is the wider version of this list.