Do ADUs require solar?

It depends on the project type. Newly constructed dwelling units in California — which can include certain new detached ADUs — may be required to include a solar photovoltaic (PV) system under the energy code, while many ADUs and most garage conversions fall under common exceptions. Solar rules and exemptions shift between code cycles and project conditions, so confirm what applies to your specific ADU with your local building department.

When solar applies — and when it doesn't

The solar mandate flows from the requirement that newly built dwelling units carry on-site PV. For ADUs, the practical lines look like this:

• New detached ADUs — may be required to include PV, with system size typically calculated from conditioned floor area and the local climate zone.
• Garage conversions — classified as alterations rather than new construction, so they are generally not subject to the new-construction solar requirement.
• Conversions of existing interior space and many JADUs — likewise fall under alteration rules.

Common exceptions even for new construction

Several recognized exceptions can reduce or eliminate the PV requirement on a qualifying new ADU:

1. Existing PV on the property — if the main home already has a solar array large enough to cover the ADU's calculated requirement.
2. Insufficient solar access — shading, obstructions, or roof orientation that leaves too little usable solar area.
3. Small available roof area — limited unshaded roof can cap or excuse the requirement.

Even when a physical PV system isn't required, plans generally must show solar-ready conduit, and many new ADUs also face battery- or energy-storage-ready (ESS-ready) provisions under the current code.

Two example scenarios

Because the rules turn on project type and site conditions, two similar-looking projects can land very differently:

• New 900 SF detached ADU, sunny unshaded roof, no existing solar. This is the classic case where PV is most likely required — the system is sized to the conditioned area and climate zone, and the electrical plans show the solar-ready and (where applicable) ESS-ready infrastructure.
• 500 SF garage conversion. Treated as an alteration, so the new-construction solar mandate generally doesn't apply — though solar-ready conduit and other energy-code items may still be expected.

The takeaway: don't assume your ADU does or doesn't need solar based on a neighbor's project. Verify against your own project type, roof, and any existing array.

How solar shows up on your plans

The MEP set provides the electrical infrastructure, while the PV system itself is designed and installed by a solar contractor. On the electrical plans, that typically means:

• Solar-ready conduit routing and panel provisions.
• Reserved breaker space and, where ESS-ready rules apply, a dedicated subpanel with identified backup circuits and conduit for a future battery.

Because the solar requirement is tied to the energy code, it's closely connected to your Title 24 report — see the ADU Title 24 Guide and Title 24 Reports. We coordinate the solar-ready infrastructure in your Full MEP Package so your electrical plans match the CF1R. Solar rules and exemptions are among the more frequently revised parts of the code, so verify current requirements for your project type before finalizing the design.