Title 24 for JADU vs ADU: What's the Difference?

Accessory Dwelling Units (ADUs) and Junior Accessory Dwelling Units (JADUs) are both paths to adding a second living unit on a single-family lot in California, and both require Title 24 energy compliance documentation — but the specifics differ in ways worth understanding before you start planning.

A JADU is capped at 500 square feet and must be constructed within the existing walls of the primary residence — it cannot be a new freestanding structure or even a bump-out addition. JADUs typically share at least some systems with the main house (often the bathroom, occasionally connecting through an interior doorway) and are required to include an efficiency kitchen at minimum.

An ADU has no such size restriction tied to the primary residence's existing footprint (though local zoning sets its own size caps, commonly 1,200 sq ft or based on lot size), and it can be entirely new construction — detached in the backyard, attached to the main house, or converted from existing space like a garage.

From a Title 24 standpoint, this distinction matters because of how the compliance forms are structured. JADU projects, given their smaller scope and the requirement that they sit within an existing structure, commonly use a CF1R-ADD (Addition) or CF1R-ALT (Alteration) form, reflecting that they're modifying an existing conditioned or unconditioned space rather than constructing an entirely new building envelope.

Detached ADUs, being effectively small standalone homes, are generally evaluated more like new construction — a complete envelope, independent HVAC system, and water heating, modeled as their own building even if zoning treats them as accessory to the main house.

Attached ADUs fall somewhere in between, depending on how much of the building envelope and systems are newly constructed versus shared with the existing residence.

In all three cases, the underlying requirement is the same: a signed Title 24 report demonstrating compliance with California's energy code for your climate zone, submitted as part of the building permit application. The specific form and modeling approach simply reflects the nature of the construction involved.