California's Title 24 energy code divides the state into 16 climate zones. Climate Zone 3 (Bay Area Coast) covers San Francisco, Oakland, San Mateo, Santa Cruz, and the inner Bay. Your zone determines the exact kW per square foot of conditioned floor area required on a new ADU.
Title 24 multiplies your ADU's conditioned floor area by a climate-zone-specific kW factor to set the minimum required solar system size. Marine-influenced climate with cool summers and consistent year-round production (~1,500 kWh/kW/year).
Most ADUs in Climate Zone 3 land in the 1.6–3.8 kW range — typically 4 to 10 modern (~400W) panels.
Annual solar production in Climate Zone 3 is driven by local irradiance, temperature, and shading. Marine-influenced climate with cool summers and consistent year-round production (~1,500 kWh/kW/year). Expect roughly 1,400–1,700 kWh per installed kW per year for typical south-facing roofs.
Title 24-compliant ADU solar packages range from $4,000 to $15,000 in Climate Zone 3. Pricing is driven primarily by system size, panel quality, and battery — not climate zone itself. HDM financing typically reduces effective cost by ~40%.
Climate Zone 3 (Bay Area Coast) covers San Francisco, Oakland, San Mateo, Santa Cruz, and the inner Bay. The California Energy Commission publishes the full ZIP-to-zone mapping.
Climate zones with hotter summers or more cloud cover tend to require slightly larger systems per square foot. Climate Zone 3 ADUs typically need 1.6–3.8 kW.
Yes — enter your ZIP code on our solar cost calculator. We map every California ZIP to its Title 24 climate zone automatically.