Clean Energy SF: San Francisco, fog then sun, est. 2026

Vol. 1 - No. 14 - Thursday, September 24, 2026 - Free to readers

Policy ยท Analysis

New homes in San Francisco carry solar by law, and the fine print decides how much

California requires most new homes to be built with rooftop solar. In a city of foggy, shaded, often north-facing roofs, the exemptions and the sizing rules do most of the work, and batteries change the math.

Filed October 3, 2026 By the Clean Energy SF editors Reading time: 6 minutes

I. What the law actually requires

If a contractor just handed you a permit set for a new house or a backyard in-law unit in the Sunset, somewhere in that stack is a page for rooftop solar you probably did not ask for. Since the start of 2020, California has required most new homes to be built with a solar electric system already on the roof. The requirement rides along with the building permit, so it is usually settled long before you pick a paint color.

The rule is real, and in a city of north-facing Victorian roofs, summer fog off the Pacific, and lots hemmed in by taller neighbors, the fine print does a lot of work. A roof that is too small, too shaded, or pointed the wrong way can shrink the requirement or remove it. This desk hears the question two ways: does my new place have to have panels, and if so, how big, and who gets to decide. Both answers run through one document, the state energy code known as Title 24, and through the people at the permit counter who apply it.

II. The sizing rule, and who it lets off the hook

Title 24, Part 6, the California Building Energy Efficiency Standards, is where the requirement lives. The California Energy Commission (the state agency that writes building energy rules) updates it about every three years, and the 2019 edition, in effect since January 1, 2020, is the one that first told builders of most new low-rise homes, meaning houses and apartment buildings of three stories or fewer, to include a solar photovoltaic system (panels that turn sunlight into electricity). Nobody picks the system size by feel. The code sets it with a formula that scales with the home's conditioned floor area (the heated and cooled living space) and a factor for the local climate zone.

Exemptions are where many San Francisco roofs actually land. San Francisco sits in California Climate Zone 3, a mild, foggy coastal band, so the per-home target tends to run smaller than it would in the hot Central Valley, and once you subtract fire-code setbacks, vents, and shade from trees or taller buildings, the usable roof can shrink fast. Roofs with too little unshaded area can be excused, and there are paths to meet the rule with community solar (a shared offsite array you buy into) where that option exists. The honest summary: the mandate is firm, but it bends to what a given roof can hold, and the permit reviewer signs off on which case you are in.

III. Where batteries enter the math

Panels alone made more sense under the old net metering deal, where the utility credited exported midday power at close to the retail rate. That changed with the state's Net Billing Tariff, often called NEM 3.0, which the California Public Utilities Commission approved for the big investor-owned utilities and which took effect in April 2023. Under it, power you send to the grid in the sunny afternoon is generally worth much less than power you pull back after dark, which is roughly when San Francisco households use the most.

That spread is what makes a home battery pencil out for some owners: you store the cheap afternoon solar and use it in the evening instead of selling low and buying high. San Francisco adds a wrinkle, because most residents buy their electricity through CleanPowerSF, the city's community choice program run through the SFPUC, rather than straight from the incumbent utility, and the credit you earn for exports depends on your specific rate plan. Before you add storage, it is worth pricing the system with and without a battery on your actual plan, because the answer is not the same for every household.

IV. Worth watching this month

1. Watch the California Energy Commission's schedule for the next Energy Code cycle, which is expected to take effect in 2026, since each update has nudged the solar and battery rules.

2. Check whether your project's permit set lists a solar exemption, and ask the plan reviewer which one and why, before framing starts.

3. If you are weighing storage, pull your current CleanPowerSF rate and its export credit before you sign a battery contract, because the economics hinge on it.

4. Keep an eye on California Public Utilities Commission proceedings touching the Net Billing Tariff, since the export credits that drive battery payback can shift with future decisions.

Frequently asked questions

Does every new home in San Francisco have to have solar?

Most new low-rise homes do, but not all. Small, heavily shaded, or awkwardly oriented roofs can qualify for a reduced size or an exemption, and the permit reviewer decides based on the plans.

Who decides how big my system has to be?

The size comes from a state formula tied to your home's floor area and climate zone, not from the installer's preference. San Francisco's mild Climate Zone 3 generally means a smaller target than hotter inland areas.

Do I have to add a battery?

For a standard new single-family home, storage is generally not required, though newer code editions require it for some larger or nonresidential buildings. Many owners add one anyway because the current export rules make evening use of stored solar more valuable.

Does this apply to a backyard ADU?

It can. Accessory dwelling units and additions can trigger the solar requirement depending on their size and the scope of work, so ask your designer early where yours falls.

References