Solar Requirements for ADUs

"Wait — does my ADU need solar panels?" Maybe. The rule splits cleanly.

New construction: generally yes. California's energy code requires solar photovoltaic systems on newly constructed dwellings, and a ground-up detached ADU is one. The system is sized to the ADU's modest expected usage — typically a small array, often 2–4 panels' worth for a compact unit, not a roof-covering installation. Budget roughly $5K–$12K depending on size and site.

Conversions: no. Garage conversions and ADUs created within existing space aren't "newly constructed" for this purpose — no solar requirement. One more quiet economy of the conversion path.

Where the panels go — three options:

1. On the ADU's roof — simplest, if orientation and shading cooperate.
2. On the main house's roof — allowed, and often better: bigger, better-oriented surface. The system just has to be added to serve the new unit.
3. Existing solar counts. If your home already has a system with adequate capacity (or you're expanding it), that can satisfy the requirement — bring your solar documentation to design.

Exceptions exist for genuinely shaded or unsuitable roofs through the compliance process — your Title 24 consultant handles the math.

Planning notes: batteries aren't required (but pair well if you're already installing); solar interacts with your electrical design, so it belongs in the plan set from the start, not bolted on after; and if a separate meter is in your plans, tell your solar designer — it affects how the system interconnects.