Do ADUs require solar under Title 24?

Sometimes — and the answer depends on the project. California's energy code requires solar photovoltaic (PV) systems on many new dwelling units, but ADUs benefit from several important exceptions. Many newly built detached ADUs end up not requiring their own PV system, while others do. The deciding factors are the project type, the roof, and the main home's existing solar.

When solar may be required

For certain newly constructed detached ADUs, a PV system may be required, with the system size typically calculated from the conditioned floor area and the climate zone (California has 16 climate zones, each with different solar and energy characteristics). Where it applies, the requirement is part of the Title 24 compliance package.

Common ADU exceptions

Several widely used exceptions can remove or reduce the PV requirement:

• Existing solar on the main home. If the primary residence already has a PV system large enough to cover the ADU's calculated requirement, a separate ADU system may not be needed.
• Insufficient solar access. If the roof is too shaded, obstructed, or poorly oriented to host a viable array, a reduction or exception may apply.
• Limited available roof area. Small ADU roofs with little usable solar zone may qualify for an exception.
• Conversions and certain alterations. Garage conversions and similar alteration projects generally do not trigger the new-construction solar requirement.

Solar-ready and storage-ready provisions

Even when a PV system isn't required up front, plans commonly must show solar-ready conduit — a pathway and panel provisions for a future array. Many new ADUs may also be subject to battery/energy-storage-ready (ESS-ready) provisions depending on the code cycle and project type.

On the electrical plans, that means showing conduit routing, reserved panel space, and any identified backup circuits. The actual PV system design and installation is handled by a solar contractor; the MEP plans provide the infrastructure and the CF1R documents the requirement or the exception relied upon.

What to do

1. Confirm whether your ADU is new detached construction or a conversion.
2. Check whether the main home already has qualifying solar.
3. Assess roof shading, orientation, and available area for an exception.
4. Have the CF1R document the requirement or the specific exception.

Because solar rules and exceptions are sensitive to the code cycle and local amendments, confirm the specifics with your local building department. We document the applicable solar requirement or exception in the registered CF1R, available as a +$240 Title 24 add-on alongside your MEP plans — see California ADU requirements.