California Title 24 Solar Mandate Calculator

Yes. Since January 1, 2020, California's Building Energy Efficiency Standards — Title 24, Part 6 of the California Code of Regulations, adopted by the California Energy Commission (CEC) and enforced by local building departments — have required most new low-rise residential buildings to include a solar photovoltaic system. The required size depends on the home's climate zone, conditioned floor area, and number of dwelling units. Since then, the CEC's three-year update cycles have carried the mandate well beyond single-family homes: high-rise multifamily and many nonresidential buildings now have solar and battery-storage requirements of their own. The standards in force today are the 2025 code cycle, effective January 1, 2026.

The calculator on this page gives you the number that whole process starts from: your home's minimum required PV size in kilowatts, with and without battery storage.

The solar mandate is not a one-time 2020 rule — the CEC updates the Title 24 energy code roughly every three years, and each cycle has widened its reach.

The 2025 cycle, in force since January 1, 2026, keeps the residential sizing method this calculator uses and extends solar and battery-storage requirements across more nonresidential and high-rise multifamily project types. If you're building a standard low-rise home, duplex, or townhome, the formula below is still your formula — but if your project is multifamily high-rise or commercial, it falls under separate provisions this calculator doesn't cover.

Here's the part most searchers get wrong: for a typical new low-rise single-family home, Title 24 does not require a battery. Storage is a compliance option the code rewards — install at least 7.5 kWh of JA12-compliant battery storage and your required solar array shrinks by 25%. The 2025 cycle also adds battery-ready wiring and space provisions for some multifamily and nonresidential projects, which is preparation for storage rather than a requirement to install it.

Whether the trade is worth it comes down to more than compliance math. Under California's current net-billing rules, solar exported to the grid earns far less than it once did, so storing your afternoon surplus and using it in the evening is where the economics have moved — a battery that shrinks your required array often pays its way in avoided evening rates and outage backup on top of the code benefit.

If you're weighing how much storage makes sense beyond the 7.5 kWh code minimum, our battery bank sizing calculator sizes a bank from your actual daily loads rather than the code floor.

This calculator gives you the code-minimum number. A real design goes further: it maps irradiance, shading, and roof angle to place panels where they'll actually perform, and it accounts for the fire and ridge setbacks your jurisdiction requires — the reason people spec a roof full of panels and then get a permit rejection for space they can't legally use.

The low-pressure path: see what a complete kit sized to your number would cost first, then talk to a solar design technician only if it fits your budget and goals. Unbound has spent 20 years equipping DIYers and professional installers with professional-grade equipment done right — you're not figuring this out alone.