For California Energy Code purposes, the work’s project state can change the compliance route. The California Energy Commission’s 2025 ADU FAQs distinguish a detached new structure, an addition that increases conditioned area or volume, and an alteration to an existing conditioned space. The distinction is useful for planning a code review; it does not replace the local building department’s classification or a complete energy analysis.
Classify the work before choosing a checklist
| Project description | Energy Code treatment described by the CEC | What still needs project review |
|---|---|---|
| New detached ADU | New construction under the new-building path | Applicable sections, climate zone, permit date, design, and local interpretation |
| Attached ADU that adds conditioned area or volume | Addition | Exact scope and applicable addition provisions |
| Garage or other previously unconditioned space converted to conditioned living space | Addition when conditioned floor area and volume increase | Existing conditions, scope, components, and local application |
| Existing conditioned space converted to an ADU or JADU | Alteration; requirements may be triggered when covered components are changed | Which components change and which alteration provisions apply |
The CEC 2025 ADU FAQ defines these paths and links them to the relevant Title 24 sections. Do not infer that two physically similar rooms have the same path: whether space is conditioned and what the work changes can matter.
Review the energy systems that the path affects
The CEC FAQ identifies project-specific questions about ventilation, space conditioning, water heating, electric-ready provisions, solar photovoltaic requirements, and battery-energy-storage readiness. Some requirements differ between a newly constructed detached unit and an attached addition. For example, the FAQ says the 2025 Energy Code’s photovoltaic treatment differs for those two project types. The FAQ also distinguishes factory-built housing from HUD-certified manufactured homes; neither label alone answers every local installation or code question.
These topics should be read with the exact adopted provisions and the unit’s permit record. A manufacturer, contractor, or existing primary-home system cannot determine compliance without the authority’s classification, applicable code sections, system design, and any required verification or diagnostic testing.
Keep the energy review separate from other approvals
An energy-code result does not establish zoning eligibility, fire safety, utility service capacity, installation approval, or occupancy. A detached unit may have separate utility connection questions even when the Energy Code permits a particular compliance approach. A conversion may also trigger building, fire, electrical, plumbing, or ventilation review unrelated to the energy classification.
Questions for the local building department
Bring a scope description showing whether the unit is detached, attached, a conversion of conditioned or unconditioned space, or factory built. Ask which 2025 Energy Code sections apply, how the authority classifies the unit, what climate-zone and permit-date provisions control, what calculations or field verification are required, and which other codes need separate review. The CEC FAQ is a current California-wide reference, not a finding that any individual design complies.