Do ADUs Need Title 24 in California?
Yes — in almost every case. An accessory dwelling unit creates conditioned living space, which brings it under Part 6 of the California Energy Code, so the permit application needs energy compliance documentation.
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The requirement attaches to the work, not the label
Calling a project an ADU does not by itself decide what the Energy Code asks for. What decides it is whether the unit is being built from scratch, carved out of space that was never heated or cooled, or made from rooms that were already conditioned. All three normally need documentation. They do not follow the same path through the code.
The three cases
A newly constructed detached ADU is treated as a new low-rise residential building. It has to meet the new-construction requirements in full, and that includes the solar photovoltaic provisions, subject to the exceptions the code lists.
An ADU made by converting unconditioned space — most often a garage — is newly conditioned space, and the Energy Code treats it as an addition. The requirements are the addition provisions rather than the new-construction ones, and the solar requirement does not attach.
An ADU made from space that was already conditioned, such as a conditioned basement or a finished pool house, is an alteration. That is a third set of rules again, generally the narrowest of the three, because the space was already inside the thermal envelope.
What this means in practice
The first question worth answering on any ADU is which of those three you have, because it changes the target the design is measured against and it changes what has to be installed. A design built against new-construction numbers when the project is really an addition is over-engineered; the reverse fails plan check.
The current standards apply to projects whose permit application is submitted on or after 1 January 2026, so a set of calculations prepared under the previous edition does not automatically carry over to an application filed now.