What is Title 24?
Title 24 is the California Building Standards Code. It sets the baseline for how buildings are designed and constructed throughout California.
Title 24 covers many different building systems: structure, plumbing, electrical, mechanical, and more. For most homeowners planning an ADU, the part that receives the most attention is the Energy Code, which is Part 6 of Title 24.
The California Energy Commission (CEC) publishes and maintains the Energy Code. The CEC updates the standards every three years, publishing new code cycles with names like "2022 Energy Standards," "2025 Energy Standards," and so on. These standards set requirements for insulation, windows, HVAC systems, lighting, water heating, and other energy-related equipment in new buildings and significant renovations.
Why Title 24 matters for ADUs
ADUs are subject to the Energy Code. Compliance is not optional—it is a required part of the permit process.
Energy requirements affect design decisions, equipment choices, insulation thickness, window specifications, HVAC system selection, water heating strategy, and overall project cost. A heat pump system costs more than a gas furnace. Better insulation increases material costs. High-efficiency windows are more expensive than standard windows.
If you plan for energy compliance early in the design phase, you build the requirements into the budget and layout from the start. If you treat energy compliance as a last-minute detail, you risk costly design changes or value engineering that cuts other project features.
Working with an energy consultant or qualified designer early helps you understand the cost impact and choose equipment and strategies that work for your budget and goals.
Which code cycle applies
The key date for determining which energy code cycle applies is the permit application date—not the design date, not when you start construction, and not when you finish construction.
The permit application date is when your complete permit application is submitted to the building department. This is the official date the building department receives all required documents and plan sets.
The California Energy Commission states that the 2025 Building Energy Efficiency Standards apply to permit applications submitted on or after January 1, 2026. If you submit your permit application on January 1, 2026 or later, the 2025 standards apply to your project.
This timing is critical. If you want to qualify for a particular code cycle, you must submit your complete application by the deadline. Homeowners planning projects for early 2026 should confirm their target application date with their building department now.
What the 2025 Energy Code changes
These key changes apply to permit applications submitted on or after January 1, 2026:
Expanded use of heat pumps
Heat pumps (including air-source and ground-source) are now strongly encouraged in newly constructed residential buildings. The code recognizes heat pumps as an efficient alternative to gas furnaces and heat-only systems.
Electric-readiness requirements
New construction must be designed with electric-ready infrastructure, allowing for future conversion or addition of electric equipment without costly retrofits.
Strengthened ventilation standards
Ventilation requirements have been updated to improve indoor air quality. Mechanically ventilated units must meet specific air exchange rates and filtration levels.
Updated insulation requirements
Wall, ceiling, and floor insulation R-values have been adjusted based on climate zone. Some areas see increased requirements; others may see modest reductions.
Solar and battery storage provisions
The code continues to encourage solar photovoltaic (PV) systems and battery storage. For some buildings, solar is required unless specific exemptions apply.
Common Title 24 topics for ADU projects
These are the Title 24 requirements that affect most ADU designs:
HVAC system selection
Choosing between heat pump systems (mini-splits, ducted, or central air-source systems) versus traditional gas furnaces. Heat pumps meet 2025 standards more easily.
Insulation and envelope requirements
Minimum R-values for walls, ceilings, floors, and foundations. Requirements vary by climate zone. Air sealing and thermal breaks are also part of the envelope specification.
Window specifications
U-factor and Solar Heat Gain Coefficient (SHGC) requirements limit heat loss and solar gain. Climate zone affects the specific values your windows must meet.
Water heating
Heat pump water heaters are now the preferred approach for new construction. Gas water heaters are also allowed but are less favorable under the code.
Lighting requirements
High-efficacy lighting fixtures and controls. Interior lighting must meet specified efficacy levels; exterior and specialized lighting have their own requirements.
Solar/PV requirements
For some newly constructed residential buildings, rooftop solar photovoltaic systems are required unless exemptions apply based on roof condition or shading.
Ventilation standards
Mechanical ventilation sizing, ductwork requirements, filter specifications, and outdoor air flow rates. Ventilation must be continuous or demand-controlled per the code.
Compliance documentation
Energy compliance must be documented as part of the building permit submittal. This documentation is reviewed by the building department before a permit is issued, and it is verified by inspectors during construction.
Most ADU projects use the CF-1R form (Certificate of Compliance for Residential Buildings) to show that the design meets Title 24 requirements. This form is prepared by an energy consultant, HERS rater, or a qualified designer who understands the code.
The CF-1R document includes:
- Building envelope details (insulation, windows, air sealing)
- HVAC system description and efficiency ratings
- Water heating system details and efficiency
- Lighting plan and fixture efficacy
- Mechanical ventilation specifications
- Solar and battery storage information (if applicable)
- Climate zone, building orientation, and other site information
The building department (plan examiners) review the CF-1R and construction documents to verify compliance before issuing the permit. After the permit is issued, the building inspector verifies during construction that the installed materials and equipment match what was approved in the compliance documents.
The cost to prepare compliance documentation varies, but it is typically a few hundred to a few thousand dollars depending on project complexity. This cost should be included in your overall budget from the start.
New construction vs conversion
Title 24 requirements vary depending on whether your ADU is new construction or a conversion of existing space.
New detached ADUs are considered new buildings and must meet the full Energy Code requirements. This includes all the topics above: HVAC, insulation, windows, water heating, lighting, and ventilation.
Conversion ADUs and garage conversion ADUs have different compliance paths. The scope of work—how much of the building envelope you are modifying—affects which requirements apply. For example, if you convert a garage into a unit but keep the existing walls and roof, you may be able to use an "existing building alteration" pathway that is less stringent than new construction, though you still must meet certain envelope and HVAC upgrades.
The specific requirements depend on the scope of work, the existing conditions, and your local building department's interpretation of the code. An energy consultant can help you understand which compliance path applies to your project type.
Common mistakes with Title 24
Homeowners planning ADUs often overlook energy compliance in ways that cause problems:
Treating energy compliance as a late detail
If you wait until after design is complete to check Title 24 requirements, you risk discovering that your HVAC choice, insulation level, or window spec does not meet the code. Fixing this requires redesign, equipment changes, and delays. Including an energy consultant early prevents this.
Not checking which code cycle applies to permit timing
If you submit your permit application on December 31, 2025, the 2022 standards apply. If you submit on January 1, 2026, the 2025 standards apply. If you are unsure of your timeline or target permit date, confirm with your building department which code will apply.
Assuming the contractor handles everything
Contractors are skilled at building to plans, but they typically do not prepare energy compliance documentation or interpret the Energy Code. You need an energy consultant, HERS rater, or qualified designer to prepare the CF-1R and ensure your specification meets Title 24.
Underestimating the cost impact of energy requirements
Heat pump HVAC systems, upgraded insulation, high-efficiency windows, and heat pump water heaters cost more than gas-based alternatives. If you do not budget for these upfront, you will be surprised at permit review or construction start.
Not coordinating Title 24 with the overall design set
Energy compliance affects ductwork routing, window sizing, foundation details, roof framing (for ventilation and solar), and electrical infrastructure. These details must be coordinated with the architectural, structural, and mechanical plans from day one.
Recommended next steps
From here, most readers should explore one of these pages next:
This page is for general educational purposes only. California Energy Code requirements, code cycles, and local implementation can change. Always verify project-specific requirements with the relevant building department, an energy consultant, and qualified professionals.