Title 24 ADU Requirements

When planning to build an Accessory Dwelling Unit (ADU) in California, one of the most important regulatory frameworks to understand is Title 24 of the California Code of Regulations. Title 24 sets statewide standards for energy efficiency, water use, ventilation, and building safety — all aimed at reducing the environmental impact of residential construction while improving occupant comfort.

For ADUs, complying with Title 24 is not optional. Whether you're building a detached backyard unit, converting a garage, or adding an internal unit to an existing home, energy compliance is a mandatory part of the building permit process. Failure to meet these standards can delay your project, increase costs, or result in denial of occupancy certification.

This article provides a comprehensive overview of Title 24 requirements as they apply specifically to ADUs. We'll cover how these regulations influence building design, material selection, mechanical systems, and more — helping homeowners, builders, and designers make informed decisions that ensure both compliance and long-term energy savings.

This article aims to clarify the key technical requirements of Title 24 as they pertain to ADU construction, providing homeowners and developers with a foundational understanding of these essential regulations.

2. What Is Title 24?

Title 24 refers to the California Building Standards Code, a comprehensive set of regulations governing the design and construction of buildings across the state. Its primary goal is to ensure public safety, health, and general welfare through standardized building practices. Title 24 encompasses various parts, each addressing specific aspects of construction. For ADUs, the most relevant sections focus on energy efficiency (Part 6), as well as structural, electrical, plumbing, and mechanical codes. Part 6, specifically the Energy Efficiency Standards, is critical for ADU projects, dictating how buildings must be designed and constructed to minimize energy consumption, enhance occupant comfort, and reduce environmental impact. Developed by the California Building Standards Commission and updated every three years, Title 24 includes provisions for structural safety, fire protection, energy conservation, accessibility, and sustainability.

One of the most critical components of Title 24 for ADU construction is Part 6 – the Building Energy Efficiency Standards. These standards were created to reduce California’s energy consumption and greenhouse gas emissions by setting minimum performance criteria for residential and non-residential buildings.

Title 24 doesn’t just focus on energy consumption during daily use — it also addresses how a building is constructed, including insulation levels, air sealing, and mechanical system performance. It requires builders and designers to consider California’s unique climate zones and tailor energy systems accordingly.

For ADUs, this means that every component — from windows and water heaters to lighting systems and ventilation — must meet efficiency targets outlined in Title 24. Understanding these standards early in the planning process is key to avoiding costly redesigns and permit delays later on.

3. How Title 24 Applies to ADUs

Title 24 applies to virtually all new construction in California — and that includes Accessory Dwelling Units (ADUs). Whether you’re building a freestanding unit in the backyard (detached ADU), converting a garage or basement (conversion ADU), or creating a unit within or attached to your primary residence (attached ADU), energy compliance is required. However, the specifics of these requirements can vary based on several factors, including the climate zone where the ADU is located, the size of the unit, and its type (detached, attached, or conversion).

A common pitfall in ADU projects is underestimating or misunderstanding the Title 24 requirements early in the design phase. This can lead to costly redesigns and delays later in the process. It's crucial to consider these energy efficiency standards from the outset to ensure a smooth and compliant project.

The scope and depth of Title 24 requirements can vary depending on several factors:

• Type of ADU: Detached new-construction ADUs typically face the most stringent energy requirements. Conversion or internal ADUs may have reduced compliance obligations, especially if the structure was previously permitted and insulated to code.
• Climate Zone: California is divided into 16 distinct climate zones, each with its own energy performance standards. The zone in which your property is located directly affects requirements for insulation, windows, HVAC systems, and more.
• Size of the Unit: Some requirements, such as solar panel installation, are triggered only when an ADU exceeds a certain square footage threshold (e.g., 750 sq. ft.).
• Project Scope: Whether you're building from the ground up or simply converting an existing space will determine which parts of the ADU must comply with the current Title 24 standards.

It’s important to note that even when converting existing space into an ADU, any new systems (like HVAC, lighting, or water heaters) still need to meet current energy efficiency standards. Working with a Title 24 consultant or energy specialist early in the design process can help identify the specific requirements your project will need to meet.

4. Energy Efficiency Requirements

Title 24 establishes detailed energy efficiency standards that affect nearly every system within an ADU. These requirements are designed to minimize energy consumption, reduce utility costs, and ensure long-term environmental sustainability. Below are the key components of the energy efficiency section of Title 24 as it applies to ADUs:

Insulation:

Proper insulation is fundamental to maintaining comfortable indoor temperatures and reducing the need for heating and cooling. Title 24 mandates minimum R-values (a measure of thermal resistance) for walls, roofs, and floors. These required R-values vary depending on California's diverse climate zones, with colder regions typically requiring higher insulation levels.

• Walls: Specific R-values are required for exterior walls, often depending on the framing type (e.g., wood stud, metal stud).
• Roofs: Roof insulation requirements are typically the highest due to heat gain in warmer months. Different roof constructions (e.g., attic, cathedral ceiling) have specific R-value requirements.
• Floors: Insulation may be required for floors over unconditioned spaces like crawl spaces or garages, with R-values varying based on the climate zone.

Windows and Doors:

Fenestration (windows and doors) plays a significant role in a building's energy performance. All fenestration (windows and glass doors) must meet specific performance criteria for U-factor (which measures heat transfer) and Solar Heat Gain Coefficient (SHGC) (which measures how much solar radiation passes through). These values ensure that the glazing used in ADUs limits heat transfer and solar heat gain, improving thermal comfort and reducing the need for mechanical cooling.

HVAC Systems:

Heating, Ventilation, and Air Conditioning (HVAC) systems are significant energy consumers. Title 24 mandates minimum energy efficiency standards for HVAC equipment, often expressed as SEER (Seasonal Energy Efficiency Ratio) for air conditioners and AFUE (Annual Fuel Utilization Efficiency) for furnaces. Requirements also include proper insulation and sealing of ductwork to prevent energy loss and the use of programmable or smart thermostats for better temperature control and energy savings.

Lighting:

Title 24 promotes the use of high-efficacy lighting, primarily Light Emitting Diodes (LEDs), which consume significantly less energy than traditional incandescent or fluorescent bulbs. The code also often requires automatic lighting controls, such as occupancy sensors or daylighting controls, in certain areas to reduce unnecessary energy use.

Water Heating:

Water heating is another major energy expense in households. Water heating systems must meet minimum energy efficiency standards, typically measured by Energy Factor (EF). Options include tankless water heaters, high-EF storage water heaters, and heat pump water heaters, the latter of which are strongly encouraged for their superior energy performance. Options like high-efficiency storage water heaters, tankless water heaters (which heat water on demand), and heat pump water heaters are often preferred or required to meet these standards.

Ventilation:

To ensure healthy indoor air quality, whole-house mechanical ventilation systems are required, often in accordance with ASHRAE Standard 62.2. This may involve minimum airflow rates, as well as performance testing for systems like kitchen range hoods. Balanced or continuous ventilation systems may also be necessary, depending on the design. Kitchen range hoods are also subject to testing and performance requirements for effective ventilation.

5. Solar PV Requirements

In addition to energy efficiency measures, Title 24 includes specific requirements for the installation of solar photovoltaic (PV) systems on new residential construction — including certain ADUs. The goal is to offset electricity consumption by generating clean, renewable energy on-site.

When Solar Is Required

Solar panel installation is typically required for newly constructed, detached ADUs that are larger than 750 square feet. However, there are a few exceptions:

• Smaller units (generally under 750 sq. ft.) may be exempt depending on local jurisdiction.
• Conversion ADUs or units built within an existing structure are usually exempt, as they are not considered new construction under Title 24 energy modeling rules.
• Exemptions may also apply in cases where the roof area is limited, heavily shaded, or structurally unsuitable for solar panels.

System Sizing

The required system size is determined using Title 24’s performance modeling approach. A common baseline is approximately 3 watts per square foot of conditioned space, but this may vary based on your climate zone, design characteristics, and electric usage assumptions.

Alternative Compliance Paths

If installing a dedicated PV system on the ADU is impractical, some jurisdictions allow alternative approaches, such as:

• Connecting to an existing PV system on the main residence.
• Community solar programs.
• Battery storage systems (in specific scenarios).

Before finalizing your ADU design, it’s important to verify local implementation rules with your city’s building department, as some municipalities have adopted stricter or more flexible interpretations of the state code.

In our next article, we’ll take a closer look at California’s ADU Solar Requirements — including how to calculate system size, understand exemptions, and explore cost-effective compliance options.

6. Other Requirements

Beyond energy efficiency and solar mandates, Title 24 includes additional technical requirements that may apply to ADUs depending on project scope, size, and location. These elements are often overlooked but play a key role in achieving full compliance.

Cool Roof

In certain climate zones — particularly hotter regions — Title 24 may require cool roofing materials for new construction or major additions. These materials have higher solar reflectance and thermal emittance, helping to reduce indoor temperatures, lower air conditioning loads, and extend the life of the roof. Whether this applies to your ADU depends on local climate conditions and the total area of roof work involved.

Electric-Ready Requirements

California is actively moving toward building electrification, and Title 24 supports this shift by requiring some ADUs to be electric-ready. This may include:

• Installing dedicated raceways for future electric vehicle (EV) charging stations.
• Providing outlets or circuits to accommodate electric water heaters, ranges, and dryers, even if gas appliances are used initially.

These features help future-proof ADUs and support statewide electrification goals.

HERS Testing and Verification

To ensure proper installation of energy systems, a certified Home Energy Rating System (HERS) rater may be required to inspect and test specific components. This may include:

• Duct leakage testing
• Verification of insulation installation
• Refrigerant charge testing for HVAC systems (The results must be submitted to the California Energy Commission as part of the compliance documentation).

Energy Compliance Report (CF1R)

A Title 24 energy compliance report, commonly referred to as CF1R, is a required part of the ADU permitting process. It documents how the proposed ADU meets energy standards and must be prepared using approved modeling software by a certified energy consultant or designer. Without this report, a permit cannot be issued.

7. Documentation and Inspection

Successfully navigating Title 24 compliance for an ADU project doesn’t end with design — it also involves thorough documentation and inspections at key stages of construction. These steps ensure that the building is constructed according to approved energy standards and is eligible for occupancy certification.

Preparation of Compliance Documentation

Before submitting plans to the local building department, a Title 24 energy compliance report (CF1R) must be completed using approved software such as EnergyPro or CBECC-Res. This report outlines how the design complies with energy performance standards and includes inputs such as:

• Insulation values
• Window and door specifications
• HVAC and water heating systems
• Lighting and ventilation designs

The CF1R becomes part of the official permit submittal package.

Construction Verification

During construction, the builder or project manager is responsible for implementing all energy features as outlined in the CF1R. Any deviations from the original plan may require revisions and updated documentation.

In addition, certain energy measures require field verification and diagnostic testing by a certified HERS rater. Common items that require testing include:

• Duct leakage
• Insulation quality and placement
• Airflow rates in ventilation systems
• Refrigerant charge and airflow for HVAC equipment

Final Inspection and Sign-Off

Once construction is complete, the local building inspector will conduct a final walkthrough. This includes checking that:

• All installed systems match the compliance documentation
• Lighting and control systems function as required
• HERS verification (if required) has been completed and reported

Only after passing this final inspection will the jurisdiction issue a Certificate of Occupancy, legally allowing the ADU to be rented or inhabited.

8. Tips for Homeowners and Builders

Complying with Title 24 for an ADU project may seem complex, but with early planning and the right team, it can be a smooth and cost-effective process. Here are some practical tips to help homeowners and builders navigate compliance with confidence:

1. Involve Energy Consultants Early

Working with a certified energy consultant or designer from the beginning of your project ensures that your plans align with Title 24 requirements. Early modeling can identify potential compliance challenges and help you optimize design choices to avoid costly revisions later.

2. Choose a Title 24–Savvy Designer or Architect

Not all designers are familiar with the intricacies of California’s energy code. Hiring professionals who have experience with ADUs and Title 24 can significantly reduce delays during permitting and construction.

3. Account for Climate Zone Variations

Energy standards in California vary by climate zone, so a one-size-fits-all approach doesn’t work. Be sure your team is using the correct zone when modeling insulation values, HVAC specs, and other energy measures.

4. Coordinate with Your Local Building Department

Each city or county may have slight variations in how they interpret and enforce Title 24. Some jurisdictions may even offer additional incentives or alternative compliance pathways. Always verify local rules early in the planning phase.

5. Document Everything Thoroughly

Keep organized records of your energy reports (CF1R, HERS verification forms, installer documentation, etc.) in case any questions arise during inspection or future resale. This documentation also adds value when marketing your ADU as an energy-efficient unit.

6. Plan for Electrification

Even if your ADU includes gas appliances today, planning for future electrification (e.g., electric-ready infrastructure) ensures long-term flexibility and code compliance as regulations evolve.

By staying proactive and working with experienced professionals, you can meet Title 24 requirements without sacrificing project timelines or budget — and end up with a more efficient, healthier, and future-ready ADU.

9. Frequently Asked Questions (FAQ)

The FAQ section is designed to address the most common questions that arise for property owners, architects, and contractors when planning and building Accessory Dwelling Units (ADUs) in California in accordance with Title 24 requirements. Understanding these regulations early in the project helps avoid delays, extra costs, and ensures compliance with energy efficiency and safety standards. In this section, we cover key topics such as the requirement for solar panel installation, ventilation and heating system standards, and the documentation needed to obtain permits.

10. Conclusion

Building an ADU in California offers an excellent opportunity to expand living space, generate rental income, or accommodate family — but it also comes with the responsibility of meeting the state’s progressive energy efficiency and sustainability standards.

Title 24 plays a critical role in ensuring that new residential units, including ADUs, are designed and built to reduce energy consumption, improve indoor air quality, and support California’s long-term environmental goals. From insulation and lighting to ventilation and solar panels, every component of your ADU must work together to meet these standards.

By understanding the requirements early, working with qualified professionals, and staying in close communication with your local building department, you can avoid costly delays and create a highly efficient, future-ready space.

Whether you're a homeowner planning your first ADU or a builder managing multiple projects, complying with Title 24 is not just a regulatory hurdle — it's an investment in performance, comfort, and long-term value.

Our company has years of experience navigating Title 24 requirements and supporting successful ADU projects across California. From energy modeling to HERS verification and final inspections, we’re here to help you through every step of the process. Contact us today to ensure your ADU project meets all compliance standards smoothly and efficiently.