Quick Answer: Yes — the California solar mandate (2019 Title 24 Energy Code) requires that new detached ADUs over 500 square feet include a solar photovoltaic (PV) system. The minimum solar system size is calculated based on the ADU’s conditioned floor area and climate zone (San Jose is Climate Zone 4). For a 600 sq ft detached ADU in San Jose, the minimum solar system is typically 1.5-2.0 kW DC, which at current pricing (2025) costs approximately $5,000-$8,000 installed including battery incentive options. Exceptions: garage conversions (JADUs) and interior space conversions are generally exempt from the solar mandate; detached ADUs under 500 sq ft are also exempt; attached ADUs added to the primary dwelling typically share the primary home’s solar system. The 30% federal solar tax credit (IRA) applies to ADU solar systems — reducing the after-credit cost to $3,500-$5,600.
California Solar Mandate — ADU Requirements 2025
Helpful Resources:
| ADU Type | Solar Mandate Applies? | Estimated Solar Cost |
|---|---|---|
| Detached ADU over 500 sq ft | Yes — solar PV required | $5,000 – $8,000 (before 30% ITC) |
| Detached ADU 500 sq ft or less | No — exempt | N/A |
| Attached ADU (addition to primary home) | Usually no — if primary home already has solar | May need to upsize existing system |
| Garage conversion (JADU) | Generally no — conversion exempt | N/A |
| Interior conversion (converted bedroom, etc.) | No — conversion exempt | N/A |
| 30% Federal ITC applies to ADU solar | Yes | Reduces cost by ~30% |
Quartz Construction includes Title 24 energy compliance and solar coordination in all new detached ADU projects in San Jose. We work with licensed solar installers to satisfy the mandate. CSLB #1003436 | Call (650) 749-7436.
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