Does a JADU Need a Title 24 Report?
Usually yes, but by a different route than a detached ADU. A junior accessory dwelling unit is created within an existing home, so the work is normally an alteration rather than new construction.
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Why a JADU sits differently in the code
A junior ADU is formed inside the walls of an existing single-family dwelling and is limited to 500 square feet. In Energy Code terms that usually means the floor area was already conditioned and already inside the thermal envelope, so nothing is being added — it is being reconfigured. That makes the work an alteration, and alterations are assessed on what the work actually touches rather than against a whole-building target.
Which parts of the work are regulated
The trigger is the scope. Adding or altering heating or cooling to serve the new unit is regulated. So is a new water heater, new or enlarged windows, and insulation work. Simply putting up a partition, adding a door and fitting the efficiency kitchen a JADU requires may touch very little that the Energy Code regulates — which is why the honest answer to this question depends on the drawings rather than on the unit type.
The case that changes the answer
A JADU that takes in an attached garage is not the simple case. That part of the floor area was unconditioned, so bringing it into use is newly conditioned space and falls under the addition provisions, exactly as a garage conversion ADU does. A single project can therefore be an alteration in one room and an addition in the next, and the documentation has to reflect both.
Because the answer turns on scope rather than on the label, the reliable way to settle it is to check the drawings against the current standards before the permit application goes in, rather than after a plan checker has raised it.