ADU Title 24 California: What Every Homeowner Must Know
You've done the research. You've picked your ADU design. Now your contractor drops a term you've been hearing since day one: Title 24. Here's the reality: Title 24 compliance is not optional in California. Miss a requirement and your permit gets rejected. Catch it late in construction, and you're looking at costly redesigns, delays, and a Certificate of Occupancy that never arrives.What Is Title 24 and Why It Applies to Your ADU
Title 24 refers to the California Building Standards Code, with Part 6 (Building Energy Efficiency Standards) being the section most relevant to ADUs. The CEC adopted the 2025 code cycle in September 2024, officially effective January 1, 2026. Permits submitted before that date follow the 2022 standards; anything after must meet the new requirements.
The 2025 cycle introduced significant changes: California replaced the old TDV compliance metric with Long-Term System Cost (LSC), evaluating the full 30-year cost of energy use. Heat pump water heaters are now the prescriptive baseline for new detached ADUs. A full CF1R, CF2R, and CF3R documentation package is now required — not just the CF1R alone. If your architect is still referencing the 2022 code, that's a red flag worth raising immediately.
Which ADU Projects Fall Under Title 24
- Detached new-construction ADUs — Most comprehensive requirements: solar PV, heat pump water heaters, full insulation compliance, and HERS testing
- Attached ADUs and additions — Treated similarly to new construction for newly conditioned space
- Garage and basement conversions — Classified as alterations; new mechanical systems must still meet efficiency standards, but the broader mandate generally doesn't apply
- Junior ADUs (JADUs) — Typically treated as alterations with reduced compliance obligations when built within the existing envelope
Energy Efficiency Requirements
Whether your ADU is 500 or 1,200 square feet, Title 24 sets hard requirements tied to permit approval:
- Insulation — R-values vary by California's 16 climate zones, with roof and ceiling insulation the most stringent due to summer heat gain
- Windows and doors — Must meet U-factor and Solar Heat Gain Coefficient thresholds, tightened in 2025 for hotter inland zones
- HVAC — Minimum SEER and AFUE ratings, properly insulated and sealed ductwork; California is targeting 500,000 heat pump installations in the program's first three years
- Water heating — Heat pump water heaters are now the prescriptive baseline for new detached ADUs (ADUs under 500 sq ft may qualify for an electric tankless exception)
- Lighting and ventilation — High-efficacy LED lighting, often with occupancy or daylight sensors, plus whole-house mechanical ventilation meeting ASHRAE 62.2 standards
Solar PV Requirements
Newly constructed detached ADUs generally require a solar PV system as part of the permit application — extended to ADUs in 2023 and reinforced in the 2025 cycle. System size is calculated using Equation 150.1-C based on conditioned floor area and climate zone, with a general baseline of approximately 3 watts per square foot.
Two key exemptions exist: if the sizing formula produces a requirement below 1.8 kW-dc, the mandate is automatically waived — the most commonly applied exemption in the state. A jurisdiction may also grant an exemption if your roof has limited access, heavy shading, or structural unsuitability. Garage conversions, basement conversions, and attached ADUs treated as additions are classified as alterations and aren't subject to the mandate at all.
If a standalone system is impractical, some jurisdictions allow connecting to an existing PV system on the main residence. Adding a battery to the system is also an alternative compliance path in specific scenarios — and under NEM 3.0, pairing storage with solar maximizes bill savings well beyond a solar-only system.
Additional Requirements to Know
- Cool roof materials — May be required in hotter climate zones like the Central Valley and Inland Empire to reduce indoor temperatures and AC demand
- Electric-ready infrastructure — Dedicated raceways for future EV charging and circuits for electric water heaters, ranges, and dryers, even if gas appliances are installed initially
- HERS testing — A certified rater must inspect duct leakage, insulation quality, HVAC refrigerant charge and airflow, and ventilation rates, with results submitted to the CEC
Documentation: What to Submit
The CF1R energy report is required for every ADU permit application — under the 2025 code, the full CF1R, CF2R, and CF3R package is mandatory. Prepared by a certified energy consultant using approved software, it typically costs $300–$800.
Two compliance paths exist: the Prescriptive Method, where each component must individually meet code (simpler but less flexible, sometimes pricier for custom designs), and the Performance Method, where a consultant models the ADU as a whole system, allowing trade-offs between components. Most experienced ADU builders use the performance method for its design flexibility.
After construction, a certified HERS rater must inspect and test required systems before your jurisdiction issues a Certificate of Occupancy — budget for this as a standard line item.
Why US Power
US Power's CSLB-licensed consultants handle Title 24-compliant ADU solar installations across California — sizing, permitting, installation, and utility interconnection under one roof. As California's exclusive factory-direct QCells partner, we offer American-made Tier-1 panels at 15–20% below typical market pricing, backed by a 25-year comprehensive warranty covering panels, workmanship, and performance. Most installations complete in 3–4 weeks from contract to Permission to Operate, with $0-down financing available.
The homeowners who move through this process smoothly are the ones who plan for Title 24 from day one and work with licensed professionals who treat compliance as a long-term investment in lower utility bills and higher property value.
https://uspowersolar.com/blog/adu-title-24-california