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Does my ADU need solar panels? (California)
Updated August 7, 2026 · based on the 2025 California Title 24 Energy Code · by Cali Energy
Does a California ADU need solar? A newly built detached ADU generally must include solar PV under the 2025 Title 24 Energy Code (unless the calculated size is under ~1.8 kW, or there’s too little usable roof). An attached ADU or a garage conversion is treated as an addition and is generally exempt.
✓ Based on the 2025 California Energy Code — your Title 24 analyst signs the final CF1R. See the rules ↓
Will your ADU need its own solar?
Based on the currently adopted California Energy Code (Title 24); newly built detached ADUs are generally treated as new residential construction. Verify the exact requirement and system size with your Title 24 analyst and LADBS/AHJ.
The rates and figures this calculator usestap to verify
The answer comes down to your ADU type under the 2025 Title 24 Energy Code. Here is the rule it applies and the exemptions that can still waive a detached ADU.
| Detached ADU (new) | PV generally required (treated as new low-rise residential) |
| Attached ADU | addition — generally exempt |
| Conversion (garage / existing space) | generally exempt |
| Small ADU | if the code-calculated PV size is under ~1.8 kW — exempt |
| Limited solar access | if usable solar-access roof is under ~80 sq ft — waived |
Requirements come from California’s 2025 Title 24 Energy Code, which treats a newly built detached ADU as new low-rise residential (PV required) but an attached ADU or a conversion as an addition (generally exempt). The required size uses the code’s Equation 150.1-C (conditioned floor area × climate zone); a detached ADU can still be exempt if that size is under ~1.8 kW or if usable solar-access roof is under ~80 sq ft. This is general guidance — your Title 24 analyst makes the determination on the CF1R, and permitting runs through LADBS or your city’s building authority.
How this calculator works
You pick your ADU type (detached, attached, or a conversion), your utility, and whether the main house already has solar. It then applies the 2025 Title 24 rule — detached new construction triggers the PV mandate, additions don’t — and adds notes about metering and your utility. It’s a plain-English read of the code, not a substitute for the compliance analysis.
How to read your result
“Generally required” or “generally exempt” is the starting position for your ADU type; the exemptions (small size, limited roof) and your exact scope can change it. The person who actually decides is the Title 24 analyst who signs your CF1R, and the permit is issued by LADBS or your local AHJ — treat this as preparation for that conversation.
What moves the result the most
Detached vs attached is the whole ballgame: a detached new ADU is new construction (PV required), while an attached ADU or a conversion is an addition (exempt). After that, the small-ADU and limited-solar-access exemptions can still waive a detached unit, and whether your main house’s solar can serve the ADU depends on the meter setup.
Common questions
Does a detached ADU need solar?
Generally yes — a newly built detached ADU is new low-rise residential under Title 24, so PV is required, unless the calculated size is under ~1.8 kW or usable roof is under ~80 sq ft.
Does an attached ADU need solar?
Generally no — an attached ADU is treated as an addition, which the PV mandate doesn’t cover.
What about a garage or space conversion?
Also generally exempt — converting existing space into an ADU isn’t new construction, so it doesn’t trigger the PV requirement. Always confirm against the adopted code for your permit.
Can my main house’s existing solar cover the ADU?
Not by itself, for code purposes. If a detached ADU requires PV, you add new modules under the ADU permit — and those new panels may be placed on the main house and joined to the existing system; they don’t have to serve the ADU’s meter. Meter setup (shared vs separate) matters for interconnection and billing, not for the Title 24 PV requirement.
Does it differ on LADWP vs SCE?
Yes for the credit math, not the PV mandate. LADWP is municipal with its own rate and interconnection rules; SCE uses the Net Billing Tariff (NEM 3.0). See NEM 3.0 explained.
Who makes the final call?
Your Title 24 analyst on the CF1R compliance documents, and the building department (LADBS or your city). This tool is general guidance, not a code determination.
Sources
- California Energy Commission — 2025 Building Energy Efficiency Standards
- California Energy Commission — 2025 Energy Code ADU FAQs
- California Energy Commission — 2025 Energy Code update (effective Jan 1, 2026)
- Title 24 solar sizing for homes & ADUs (equation and 1.8 kW exemption)
- EnergySage — LADWP net metering (2026)
Estimates only, not a quote. Assumptions, rates, incentives and program rules can change — confirm current details with your utility, the program administrator or a licensed professional.
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