2025 California Energy Code Updates: What Changed for ADUs?

California updates its Energy Code on a roughly three-year cycle. The 2025 Energy Code — adopted by the California Energy Commission in September 2024 and published as part of the 2025 Triennial Edition of Title 24 on July 1, 2025 — took effect January 1, 2026. It's now the active standard for permit applications submitted on or after that date. Projects whose permit applications were submitted before January 1, 2026 generally remain subject to the 2022 code cycle for that project's life. If you're not sure which cycle applies to your project, that usually comes down to your permit application date, not your construction start date — worth confirming with your building department or energy consultant if you're near the boundary.

Here's what changed at the statewide level, and where the details depend on your specific project.

At the general, statewide level, the 2025 cycle continues the shift toward electrification that started under the 2022 code. Energy budget calculations now more strongly favor heat pump equipment for both space conditioning and water heating in newly constructed single-family and low-rise multifamily buildings — meaning heat pump systems have an easier time meeting the energy budget than comparable gas equipment under the new modeling, even where gas remains legally permitted. Prescriptive envelope and ventilation requirements were also tightened in most climate zones compared to 2022, though the exact numbers vary by zone and building type.

How much this affects your project depends heavily on project type. New construction sees the most substantial changes — expanded electric-ready provisions now require pre-wiring and pre-plumbing for future heat pump water heaters and electric cooking equipment in multifamily buildings and commercial kitchens, even on projects where gas is still being installed initially. Additions, alterations, and remodels that don't rise to the level of new construction are affected less dramatically; for many smaller residential remodel projects, the practical day-to-day experience of Title 24 compliance hasn't changed as much as the headlines suggest.

Occupancy type matters too. The multifamily and commercial kitchen electric-ready provisions described above are occupancy-specific — they don't apply the same way to a single detached ADU, which is generally evaluated more like a small single-family home.

The compliance approach you use also shapes the outcome. As with prior cycles, projects can generally pursue either the prescriptive path (meeting fixed component-by-component requirements) or the performance path (whole-building energy modeling). Which path makes sense — and exactly how the 2025 changes affect your numbers — depends on your specific design, and is something your energy consultant works out project by project rather than something with a single universal answer.

Finally, local enforcement and interpretation still play a role. Individual building departments retain some discretion in how they apply and verify code requirements, and some California jurisdictions maintain their own "reach codes" that go beyond the statewide minimums. Your local building department is the final authority on what's required for your specific permit.

One thing that hasn't changed across either cycle: the baseline ADU requirement. All ADUs, regardless of size, still need full energy compliance documentation. What changes cycle to cycle is the specific efficiency targets and compliance credits available, not whether documentation is required at all.

If your project is in progress and you're not certain which code cycle your report should reflect, the safest step is to confirm your permit application date with your building department and let your energy consultant know — a report built for the wrong cycle can trigger plan-check corrections that are easy to avoid by confirming this upfront.