Title 24 ADU Requirements

What is Title 24?

Title 24 is a section of the California Code of Regulations that sets standards for the energy efficiency of new builds and greenhouse gas emissions during the construction process. These standards apply to all forms of residential construction, including accessory dwelling units. This means that if you’re building an accessory unit on your property, your plans need to be Title 24 compliant to get your permit application approved.

While compliance with Title 24 can feel daunting to homeowners, an experienced ADU builder will be more than familiar with these standards and can help ensure your ADU meets all current energy codes. This will help prevent delays in the design phase and with building permit approval, both of which can be costly.

Title 24 is California’s energy code that requires ADUs to meet efficiency standards in HVAC, insulation, lighting, and solar, ensuring long-term sustainability.

Key Energy Efficiency Requirements for ADUs Under Title 24

Title 24 outlines standards for insulation, windows, doors, HVAC systems, lighting, and water heaters to help achieve net zero energy standards for new residential construction. These requirements have changed over the years as new technology has become available and will continue to be updated in the coming years.

Some of these standards are measured using a prescriptive approach (e.g. (“Have you bought the right water heater or the right kind of window?”), while others are measured using a performance approach (e.g. “Does your system maintain an overall level of energy efficiency?”).

Improved Insulation Standards

Title 24 outlines specific insulation standards depending on your climate zone. California has 16 “zones,” with Zone 1 being the coolest and Zone 16 being the hottest. If you live in a hotter zone, Title 24 emphasizes roof and attic insulation to reduce cooling needs, while cooler zones emphasize wall and floor insulation to minimize heating demands.

Insulation is measured in R-value. The required R-value for your insulation can be anywhere from R-30 to R-49, depending on your zone and what area of the house you’re insulating. When it comes to cost, insulation with a higher R-value is generally more expensive, but can also lead to greater energy performance (which can lead to energy savings!).

Proper insulation, tailored to your climate zone, is crucial for reducing energy costs and maintaining indoor comfort year-round in your ADU.

High-Performance Windows and Doors

Doors and windows play a critical role in the overall energy performance of a residential building. Title 24 outlines standards to reduce heat transfer in hotter zones and minimize energy loss in cooler ones.

Anything with a glass pane has what’s called a U-factor. This measures the rate of heat transfer. The lower the number, the less heat transfer occurs. Title 24 states that any windows or doors installed in new primary homes or secondary units need to have a U-factor between .3 to .4, depending on the climate zone. It also mandates that doors have adequate weather stripping to prevent air leakage and drafts.

Energy-efficient windows with low U-factors help reduce heat transfer, improving climate control and meeting Title 24 compliance for ADUs.

Efficient HVAC Systems and Smart Thermostats

Unlike other areas of the country, central HVAC systems are practically a given in Southern California, and Title 24 has set strict energy efficiency standards for new and replacement systems. The 2025 Title 24 updates push for wider adoption of heat pumps, with a strong emphasis on replacing older AC units with high-efficiency heat pump systems in some single-family home alterations and additions. This shift aligns with California’s broader goal of reducing greenhouse gas emissions and moving toward electrification.

For ducted systems, ductwork in attics or other unconditioned spaces must be insulated to a minimum of R-6, with all joints properly sealed to prevent air leakage and ensure efficient heating and cooling. In addition, ventilation standards have been strengthened for multifamily buildings to improve indoor air quality, requiring better filtration and airflow management.

Smart thermostats also continue to be a mandatory component of all new builds and major renovations. As of 2023, California requires that all newly installed thermostats be programmable or remotely controllable via mobile apps to enhance energy efficiency and reduce unnecessary heating and cooling.

While these HVAC and ventilation updates may come with higher upfront costs, they provide long-term benefits, including lower energy bills, better indoor air quality, and reduced wear and tear on HVAC systems. By upgrading to a heat pump system or high-efficiency HVAC unit, homeowners can future-proof their property while ensuring compliance with California’s evolving energy standards.

Upgrading to a high-efficiency HVAC system, like a heat pump, ensures compliance with Title 24 while improving comfort and reducing energy consumption.

LED Lighting

Title 24 requires that all new residential and commercial buildings and major home renovations use energy-efficient lighting, which is often LED. It also requires automatic controls for lighting systems. These can include dimming, daylighting, or occupancy controls that automatically turn the lights off if no one is in the room.

LED lighting and automated controls reduce energy waste, helping ADUs meet Title 24 efficiency standards with cost-effective, long-term savings.

Solar Photovoltaic (PV) Systems

Solar photovoltaic (PV) systems—more commonly known as solar panels—are a core requirement under Title 24, ensuring new construction meets California’s energy efficiency and sustainability goals. All new ADUs are required to have solar panels, even if the primary residence does not already have a solar system. The exact number of panels needed depends on the size of your ADU project and its anticipated energy consumption. An experienced ADU builder can calculate your specific solar requirements to ensure compliance.

2025 Title 24 updates expand solar and battery storage requirements, particularly for multifamily and nonresidential buildings. While single-family ADUs will still require solar panels, multifamily ADUs and certain other projects may now also need battery storage to support grid resilience and energy efficiency. This change aligns with California’s ongoing push toward electrification and renewable energy integration.

Currently, battery storage is not mandated for single-family ADUs, but it is incentivized through programs like California’s Self-Generation Incentive Program (SGIP). Homeowners who install battery systems can take advantage of financial incentives to offset costs, making energy storage a valuable option for those looking to increase energy independence and backup power reliability.

Title 24 mandates solar panels for new ADUs, ensuring energy efficiency and providing homeowners with long-term energy savings.

Water Heating

Title 24 doesn’t mandate a specific type of water heater, but it does set minimum energy efficiency standards for all options. With the 2025 updates, California is placing a stronger emphasis on heat pump water heaters as part of its broader push toward electrification and energy efficiency.

If you choose a storage water heater (which holds heated water in a tank), it must meet an Energy Factor (EF) of 0.92 or greater for electric models and between 0.67 and 0.75 for gas models. Tankless water heaters, which heat water on demand, must have an EF of 0.82 or higher to comply with Title 24 standards.

While tankless and solar water heaters remain viable options, heat pump water heaters are becoming the preferred choice due to their high energy efficiency and alignment with California’s long-term energy goals. Although heat pump water heaters may have a higher upfront cost, they consume significantly less electricity than traditional electric models, reducing energy bills over time. As Title 24 continues to evolve, heat pump water heaters may become the standard for new ADUs and home additions.

If you’re planning an ADU or home upgrade, choosing a Title 24-compliant, energy-efficient water heating system will ensure long-term savings and environmental benefits while keeping your project up to code.

Heat pump water heaters are becoming the preferred choice for ADUs, offering high efficiency and aligning with California’s push for electrification.

Why Does Title 24 Matter for ADUs?

ADUs are becoming more and more popular across the state, and Title 24 ensures that the additional building doesn’t have unwanted effects on the environment by promoting renewable energy sources and reducing greenhouse gas emissions.

While this is the primary driver, Title 24 also benefits homeowners. The requirements under Title 24 ultimately help lower energy bills and, in the case of solar power and electrical bills, can eliminate some altogether eventually.

Are Solar Panels Required for ADUS? (Title 24 Solar Requirements)

Yes, in most cases, solar panels are required on ADUs. The number of solar panels required is based on your ADU’s size and anticipated energy needs. There are some exceptions, though. If your ADU has limited solar access due to shade or building obstruction, it may be exempt from Title 24’s solar requirements.

In our experience, installing solar panels is often the biggest sticking point for homeowners because it has the highest upfront costs. Luckily, state and federal tax incentives exist that can help lower the out-of-pocket costs for these units.

Most ADUs require solar panels under Title 24, but exemptions may apply based on shading, size, or existing structures.

Which ADUs Are Exempt from Title 24 Requirements?

While most ADUs are required to adhere to Title 24’s net-zero electricity guidelines, there are some exceptions. These include ADUs that:

• Have limited solar access due to shading or other obstructions, exempting them from solar panels
• Are under 500 square feet
• Are being converted from an existing structure, like a garage

Title 24 Climate Zones and How They Impact ADU Requirements

Title 24 doesn’t apply a one-size-fits-all approach to energy standards. Instead, California is divided into 16 distinct climate zones, each with specific requirements for insulation, windows, doors, HVAC efficiency, and solar systems based on regional temperatures and weather patterns.

With the 2025 Title 24 updates, higher performance margins have been introduced for single-family homes, ranging from 0.18 to 2.7, depending on the climate zone. This means that energy efficiency standards for ADUs will vary, impacting the type of insulation, heating and cooling systems, and overall energy modeling requirements homeowners must meet. For example, hotter zones may have stricter requirements for roof and attic insulation to reduce cooling demands, while cooler zones will emphasize wall and floor insulation to minimize heating loss.

Understanding your specific climate zone is essential to ensuring that your ADU meets Title 24 compliance requirements. You can see what zone you live in here. Working with an experienced ADU builder will help navigate these requirements, ensuring your project aligns with the latest energy efficiency standards while optimizing performance and cost savings.

Title 24 climate zones determine insulation, HVAC, and energy requirements for ADUs, ensuring tailored efficiency based on location.

How to Ensure Your ADU Meets Title 24 Requirements

Title 24 requirements are really that: requirements. They need to be accounted for during the design phase.

To do this, you can hire a certified energy consultant to review your building design and suggest changes before you submit for a permit. You can also use energy modeling software to verify compliance with requirements that use the Performance Approach or state-supplied tools like Energy Code Ace.

The easiest, most accurate, and most cost-effective solution, though, is to hire an experienced ADU builder in your area. They will not only be familiar with Title 24 standards, but all building standards for ADUs.

Upcoming Title 24 Updates

Title 24 is continuously evolving, with new regulations aimed at improving energy efficiency and reducing environmental impact. The latest updates were adopted in September 2024 and are set to take effect on January 1, 2026. These changes reflect California’s continued push toward electrification, clean energy, and sustainability, impacting ADU construction and home additions in several key areas.

Key 2025 Title 24 Updates

Heat Pump Adoption: California is aggressively promoting heat pumps, with a goal of 500,000 installations within the first three years of implementation. In certain cases, homeowners replacing an air conditioner in a single-family home may be required to switch to a heat pump system instead of a traditional HVAC replacement.

• Electric-Ready Requirements: Some multifamily ADUs and new construction projects must now include pre-installed electrical capacity for future electrification. This applies to kitchens, water heaters, HVAC systems, and other major appliances, ensuring homes are prepared for an all-electric future.
• Stronger Ventilation Standards: New indoor air quality regulations for multifamily ADUs require enhanced ventilation, better filtration, and improved airflow management to promote healthier living environments.
• Solar & Battery Storage Expansion: Multifamily ADUs and some other project types may now require battery storage in addition to solar panels. While battery storage is not yet required for single-family ADUs, incentives and evolving energy policies suggest this may become more common in the future.
• Implementation Timeline: These updates were adopted in September 2024 and will officially take effect on January 1, 2026.
• Expected Impact: The new regulations are projected to save $4.8 billion in energy costs over time and reduce greenhouse gas emissions by 4 million metric tons.

These Title 24 updates will shape ADU construction and home additions moving forward, emphasizing energy efficiency, electrification, and sustainable design. If you’re planning an ADU project in the next few years, working with a knowledgeable builder will ensure compliance with these evolving standards while maximizing long-term energy savings.

Common Challenges Homeowners Face with Title 24 ADU Compliance

There are 3 common challenges homeowners face when working to comply with Title 24: Navigating permitting, upfront costs, and compliance measurements.

• Navigating permitting requirements: To receive a building permit for an ADU, Title 24 regulations must be met. Failure to do so will result in permit rejection and costly resubmission fees.
• Balancing upfront costs with long-term savings: While the required materials and appliances ultimately lower a homeowner’s energy usage and save money on utility bills, they’re more expensive upfront, which can be tricky for homeowners to navigate – especially with a tight construction budget.
• Misunderstanding Prescriptive vs Performance: Compliance is measured one of two ways, depending on what you’re measuring. If you use the wrong approach, you may think something is compliant when it is not, resulting in permit rejection. Prescriptive compliance is more strict and dictates exactly what needs to be done, while performance compliance can have more flexibility in achieving an end-goal outcome.

While your local building department can help you navigate prescriptive vs. performative approaches, an ADU expert can help you navigate all 3 of these common hang-ups, keeping a project running on time and within budget despite Title 24 requirements.

Understanding Title 24 compliance early can prevent costly permitting delays and ensure your ADU meets California’s energy standards.

How Better Place Design & Build Helps You Comply with Title 24

Better Place is well-versed in zoning laws and energy code requirements as they pertain to ADUs, and it’s our goal to make the construction process as smooth as possible.

If the thought of adhering to (and paying for!) Title 24 requirements are holding you back, take a look at our most recent projects, all of which meet energy efficiency standards – then give us a call for a free consultation.