What Is Title 24 and How It Affects Insulation

Every building permit in California runs through the same gate: Title 24.

If you are planning new construction, an addition, or a renovation anywhere in the state, this code determines what flies and what gets rejected. It covers everything from structural safety and fire protection to energy efficiency and green building standards.

But most people hear “Title 24” and think it is only about energy. It is not. The California Building Standards Code contains 12 parts, and the energy code is just one of them.

This guide breaks down what Title 24 actually requires, who enforces it, which buildings it applies to, how compliance works across California’s 16 climate zones, and what changed in the latest code cycle.

What is Title 24

Title 24 is the California Building Standards Code, a collection of regulations within the California Code of Regulations that controls how buildings are designed, built, and renovated across the state.

The California Building Standards Commission (CBSC) first adopted it in 1978 after state legislation required all building standards to be unified under a single code.

Before that, construction rules were scattered across multiple titles. Architects and contractors had to dig through different documents just to figure out what applied to their project.

Title 24 fixed that problem. It pulled everything into one place: structural safety, fire protection, plumbing, electrical systems, mechanical systems, energy efficiency, accessibility, and green building requirements.

The California Energy Commission (CEC) updates the energy-related portions every three years. Local city and county building departments handle enforcement during permitting and inspections.

All new construction, additions, and alterations to both residential and nonresidential buildings in California must comply. The only exceptions are correctional facilities like jails and prisons.

What Are the 12 Parts of Title 24?

Title 24 is split into 12 parts. Each one covers a different area of building design, safety, or performance. Part 7 is currently vacant (it used to cover elevator safety, which moved to Title 8).

Here is the full breakdown:

• Part 1 – California Administrative Code: administrative regulations for all state agencies that enforce building standards
• Part 2 – California Building Code (CBC): general design and construction rules for fire safety, structural integrity, and access compliance, based on the International Building Code (IBC)
• Part 2.5 – California Residential Code: covers detached one- and two-family homes and townhouses up to three stories, based on the International Residential Code
• Part 3 – California Electrical Code: electrical design and construction standards, based on the National Electrical Code (NEC)
• Part 4 – California Mechanical Code: heating, ventilating, cooling, and refrigeration system standards
• Part 5 – California Plumbing Code: plumbing design, installation, and maintenance standards
• Part 6 – California Energy Code: building energy efficiency standards for both residential and nonresidential buildings
• Part 7 – Reserved (vacant)
• Part 8 – California Historical Building Code: standards for qualifying historical structures
• Part 9 – California Fire Code: fire safety regulations, based on the International Fire Code
• Part 10 – California Existing Building Code: rules for alterations and repairs to existing structures
• Part 11 – CALGreen Code: California Green Building Standards, with both mandatory and voluntary tiers
• Part 12 – California Referenced Standards Code: standards referenced by other parts of Title 24

Parts 2, 2.5, 9, and 10 are based on International Code Council (ICC) model codes with California-specific amendments. Parts 4 and 5 come from the International Association of Plumbing and Mechanical Officials (IAPMO). Parts 1, 6, 8, 11, and 12 are entirely California-developed codes.

What is Title 24 Part 6?

Title 24 Part 6 is formally called the Building Energy Efficiency Standards. It sets the energy performance rules for new construction, additions, and alterations across California.

The California Energy Commission adopts and updates Part 6 on a three-year cycle. The 2025 edition took effect January 1, 2026.

Part 6 is split into three sets of requirements. First, there are mandatory measures that apply to every building regardless of type or location. Second, there are performance standards (energy budgets) that change based on climate zone and building type. Third, there are prescriptive packages that give builders a checklist-style compliance path.

California has 16 climate zones, and the energy budgets are tailored to each one. A building in foggy San Francisco faces different thermal demands than one in the desert heat of Palm Springs. Part 6 accounts for that.

The code covers home insulation, lighting, HVAC systems, water heating, solar photovoltaic systems, and battery storage. It also includes indoor air quality and ventilation standards as of the 2025 update.

How Does the Prescriptive Compliance Method Work Under Title 24 Part 6?

The prescriptive path is a predefined checklist. Pick from approved materials, equipment, and methods that the CEC has already confirmed meet efficiency targets. No energy modeling needed.

It works well for straightforward projects where the builder wants a simple, fast compliance route.

How Does the Performance Compliance Method Work Under Title 24 Part 6?

The performance path uses energy modeling software to calculate whether a proposed building meets its energy budget. Builders get full design freedom as long as the total energy use stays within the budget for that climate zone.

This method is more flexible but requires an energy consultant and approved calculation tools from the CEC’s Alternative Calculation Method (ACM) manual.

What Are the Mandatory Requirements Under Title 24 Part 6?

Mandatory measures apply to all buildings, no exceptions. They include minimum R-value requirements for insulation, air sealing standards, duct sealing and testing, high-efficacy lighting, and mechanical ventilation for indoor air quality.

These baselines exist whether you choose the prescriptive or performance compliance path.

Who Enforces Title 24 in California?

Two separate bodies handle Title 24, and people mix them up constantly.

The California Energy Commission writes and updates Part 6 (the energy code). They also provide compliance tools, approved software, training, and a dedicated energy code hotline.

The California Building Standards Commission oversees the broader Title 24 framework, coordinating all 12 parts and publishing the triennial code editions.

But neither agency shows up at your job site. Local building departments, your city or county plan checkers and inspectors, are the ones who actually verify compliance. They review plans during the permit process and inspect work before granting occupancy.

Some jurisdictions enforce Title 24 more strictly than others. Metropolitan areas like San Francisco and Los Angeles were early adopters of rigorous enforcement. Other regions have been slower to catch up, partly because inspectors and building officials in some counties still lack specific training on the energy code.

State agencies like the Division of the State Architect (DSA) enforce Title 24 for public schools and state-owned buildings. The State Fire Marshal (SFM) handles fire safety provisions for certain occupancy types.

What Buildings Does Title 24 Apply To?

Title 24 applies to all new construction, additions, and alterations of residential and nonresidential buildings in California. There is no square footage minimum. If you pull a building permit, the code applies.

The only exemptions are correctional centers, jails, and prisons.

Does Title 24 Apply to Residential Buildings?

Yes. Single-family homes, duplexes, townhouses, condominiums, and apartment buildings all fall under Title 24. Since 2020, all new low-rise residential buildings must include rooftop solar PV systems. The 2025 code adds battery storage requirements alongside solar.

Does Title 24 Apply to Commercial Buildings?

Yes. Office buildings, retail spaces, warehouses, restaurants, and hotels must comply with Title 24 Part 6 energy standards plus all other applicable parts. Nonresidential buildings also require acceptance testing for lighting controls and mechanical systems, performed by certified technicians through the ATTCP program.

Does Title 24 Apply to Existing Buildings?

Only when alterations are made. A building sitting untouched does not trigger compliance. But the moment you replace windows, upgrade HVAC equipment, change lighting systems, or add square footage, the altered components must meet current Title 24 standards.

Part 10 (California Existing Building Code) and Part 8 (California Historical Building Code) provide specific rules for renovations and qualified historic structures.

What is a Title 24 Report?

A Title 24 report is a compliance document that proves a building’s design meets California’s energy efficiency standards before construction begins. You cannot get a building permit without one.

For residential projects, the report uses the CF1R form. Nonresidential projects use the PRF (Performance Report Form). Both are generated through CEC-approved energy modeling software.

A certified energy consultant or Title 24 analyst typically prepares the report once architectural plans are finalized. The report gets inserted into the plan set before submission to the local building department for permit review.

Getting it wrong or submitting it late is one of the most common reasons for permit delays in California. Plan checkers will reject incomplete or inaccurate Title 24 documentation without hesitation.

How Does Title 24 Use Climate Zones?

California is divided into 16 climate zones, each with distinct temperature ranges, humidity levels, and solar exposure patterns. Title 24 Part 6 ties its performance standards directly to these zones.

A building in Climate Zone 1 (Arcata, foggy and cool) has completely different energy budget calculations than one in Climate Zone 15 (Imperial Valley, extreme desert heat).

The prescriptive packages, insulation minimums, window specifications, and HVAC sizing all shift depending on which zone your project sits in. This is not optional. The climate zone is determined by the building’s physical address, and the CEC publishes lookup tools to identify it.

The system makes Title 24 more precise than a one-size-fits-all national code. But it also means you cannot copy compliance specs from a project in San Diego and apply them to a build in Sacramento.

What Are the Title 24 Requirements for Insulation?

Title 24 sets minimum thermal conductivity and R-value standards for walls, roofs, floors, and raised foundations. These minimums change by climate zone and building type.

Residential buildings typically need R-13 to R-21 wall insulation depending on the zone. Ceiling insulation requirements range from R-30 to R-38 in most zones. Raised floor insulation sits around R-19.

The code also requires continuous insulation in certain wall assemblies to reduce thermal bridging through framing members. Builders can choose from multiple types of insulation materials including fiberglass, cellulose, spray foam, or rock wool insulation, as long as the installed product meets the required R-value for that assembly.

The vapor barrier requirements tie into insulation placement and climate zone moisture conditions. Getting the vapor profile wrong can cause condensation problems inside wall cavities even if the R-value checks out on paper.

What Are the Title 24 Requirements for Lighting?

Title 24 Part 6 sets lighting power density (LPD) limits measured in watts per square foot. Residential and nonresidential buildings have separate standards.

For homes, all permanently installed luminaires must be high-efficacy (LED or equivalent). Kitchens, bathrooms, garages, laundry rooms, and utility spaces all have specific requirements.

Nonresidential buildings face stricter LPD caps that vary by space type. An office has a different allowance than a warehouse or a retail showroom. Lighting controls, including occupancy sensors, daylight dimming, and demand response capability, are mandatory in most commercial spaces.

Certified acceptance testing is required for nonresidential lighting control systems. A technician from an approved ATTCP provider must verify the controls work correctly before the building gets occupancy clearance.

What Are the Title 24 Requirements for HVAC Systems?

Heating and cooling equipment must meet federal and state efficiency minimums. But Title 24 goes further than baseline equipment ratings.

Duct sealing is mandatory. All ducts in residential and nonresidential buildings must be sealed and tested for leakage. Leaky ductwork wastes energy and throws off the entire building’s thermal performance.

The 2025 code cycle pushes hard toward heat pump technology for both space heating and water heating. Electric heat pumps are now the baseline pathway for new residential construction in most climate zones, reflecting California’s broader building decarbonization goals.

Mechanical ventilation standards tightened in the 2025 update too. Indoor air quality requirements now specify minimum outdoor air exchange rates for all occupied spaces.

What Are the Title 24 Requirements for Solar Panels and Battery Storage?

Since January 1, 2020 (the 2019 code cycle), all new low-rise residential buildings in California must include rooftop solar photovoltaic systems. California was the first state to mandate this.

The 2022 code expanded the solar requirement to certain nonresidential buildings and high-rise multifamily projects. It also introduced battery storage requirements for the first time, requiring most buildings with mandatory solar to include a battery energy storage system (BESS) that meets minimum rated energy and power capacity calculations.

The 2025 code builds on this by extending battery storage mandates further and tightening the sizing equations.

Buildings that are not required to install solar must still be “solar-ready,” meaning adequate roof space, conduit pathways, and electrical panel capacity must be in place for a future installation. The same solar-ready and storage-ready logic applies to commercial projects under the performance compliance path.

These requirements work alongside NEM 3.0, California’s updated net energy metering policy, which shifted the economics of solar toward self-consumption and storage rather than grid export.

What is the Difference Between Title 24 Part 6 and CALGreen Part 11?

People confuse these two constantly. They overlap in subject matter but serve different functions.

Part 6 (California Energy Code) is strictly about energy efficiency: insulation, lighting, HVAC, solar, battery storage, and water heating. Compliance is mandatory with no voluntary tiers.

Part 11 (CALGreen) is the California Green Building Standards Code. It covers a broader set of sustainability topics: water conservation, material selection, construction waste diversion, indoor air quality, and environmental quality. CALGreen has both mandatory baseline requirements and voluntary tiers (Tier 1 and Tier 2) that local jurisdictions can choose to adopt.

A project must comply with both Part 6 and Part 11’s mandatory provisions. They are not interchangeable. Meeting one does not satisfy the other.

How Often is Title 24 Updated?

Every three years. The California Building Standards Commission publishes a new triennial edition of the full Title 24 code, and the California Energy Commission updates Part 6 on the same cycle.

The current edition is the 2025 code, effective January 1, 2026. Previous editions took effect in 2020 (2019 code), 2023 (2022 code), and so on going back to the original 1978 adoption.

The three-year cycle exists because California law (the Warren-Alquist Act of 1974) requires the CEC to adopt cost-effective energy standards that reflect current technology and building methods.

What Changed in the 2025 Title 24 Update?

Heat pumps became the default for space and water heating in new residential construction. Battery storage requirements expanded, ventilation standards tightened for better indoor air quality, and the code took another step toward the state’s goal of carbon neutrality by midcentury.

What Changed in the 2022 Title 24 Update?

Battery storage mandates were introduced for the first time. Solar requirements expanded to high-rise residential and some commercial buildings. The code also encouraged electric-ready construction and improved building envelope standards.

What Changed in the 2019 Title 24 Update?

The headline was California’s solar panel mandate for new low-rise homes, a first in the United States. Buildings under this code are roughly 53% more energy efficient than those built to the 2016 standard.

How Much Does Title 24 Compliance Cost?

A residential Title 24 energy report typically costs between $200 and $500 depending on project complexity. Nonresidential reports run higher, often $500 to $2,000 or more for large commercial buildings.

The report itself is just one cost. Meeting the actual energy standards adds to construction budgets through better insulation, efficient HVAC equipment, solar PV systems, and battery storage.

But here is the thing California law requires: every measure in Part 6 must be cost-effective over a 30-year building lifespan. The CEC cannot adopt a standard unless the long-term energy savings outweigh the upfront cost. So while the initial price tag goes up, the return on insulation and efficiency upgrades is baked into the code by design.

The California Building Industry Association has supported every adopted edition of the standards, which says something about the cost-benefit math.

What Happens If a Building Does Not Comply With Title 24?

No permit. That is the short answer.

Local building departments review plans for Title 24 compliance before issuing construction permits. If the Title 24 report is missing, incomplete, or incorrect, the application gets rejected. Revisions can add weeks or months to a project timeline.

During construction, inspectors verify that installed materials and systems match the approved plans. Failing an inspection can result in stop-work orders until corrections are made.

After construction, final inspections and acceptance testing must pass before the building receives occupancy clearance. No certificate of occupancy means nobody moves in.

How Does Title 24 Compare to ASHRAE 90.1?

Most U.S. states base their commercial building energy codes on ASHRAE 90.1 (published by the American Society of Heating, Refrigerating and Air-Conditioning Engineers), either directly or through the International Energy Conservation Code (IECC).

California does not. Title 24 Part 6 is a fully independent, state-developed energy code. It predates ASHRAE 90.1’s widespread adoption and has consistently been more aggressive in its efficiency targets.

According to the American Council for an Energy-Efficient Economy (ACEEE), California leads the nation in building energy code stringency. States like Massachusetts, Vermont, and New York follow behind.

Where they overlap: both codes cover insulation, HVAC, lighting, and building envelope performance. Where they differ: Title 24 includes mandatory solar and battery storage provisions, uses California-specific climate zones instead of ASHRAE’s national climate data, and requires acceptance testing by certified technicians for nonresidential systems.

For contractors working across state lines, the jump from ASHRAE 90.1 to Title 24 compliance is significant. What passes in Nevada or Arizona will not pass a plan check in California.

What is the Role of the California Energy Commission in Title 24?

The CEC is the agency that writes, adopts, and updates Part 6 of Title 24. That is its primary role in this code.

Beyond writing the standards, the CEC provides the tools to comply with them: approved energy modeling software, compliance manuals for residential and nonresidential projects, reference appendices with technical data, and an energy code hotline (800-772-3300 in California).

The CEC also manages the Acceptance Test Technician Certification Provider (ATTCP) program, which certifies the technicians who perform required acceptance testing on lighting and mechanical systems in nonresidential buildings.

The CEC is not the same as the California Building Standards Commission. The CBSC oversees the entire Title 24 framework across all 12 parts. The CEC only controls Part 6 and the energy-related portions of Part 11 (CALGreen). Both agencies operate independently but coordinate on the triennial code cycle to publish updates on the same schedule.

FAQ on What Is Title 24

What is the purpose of Title 24 in California?

Title 24 reduces wasteful energy use in buildings across California. It sets minimum standards for structural safety, fire protection, plumbing, electrical systems, and energy efficiency. The California Building Standards Commission publishes and maintains the code.

What is Title 24 Part 6?

Part 6 is the California Energy Code, formally called the Building Energy Efficiency Standards. It governs insulation, HVAC, lighting, solar panels, and battery storage requirements for new and altered residential and nonresidential buildings.

How often does Title 24 get updated?

The California Energy Commission updates Title 24 on a three-year code cycle. The 2025 edition took effect January 1, 2026. Each update reflects new energy efficient technologies and construction methods.

Does Title 24 apply to existing buildings?

Only during alterations. If you replace HVAC equipment, upgrade lighting, swap windows, or add square footage, the changed components must meet current Title 24 standards. Untouched buildings are not retroactively required to comply.

What is the difference between prescriptive and performance compliance?

Prescriptive compliance follows a predefined checklist of approved materials and methods. Performance compliance uses energy modeling software to prove the building meets its energy budget. Both paths satisfy Title 24 Part 6.

Who enforces Title 24?

Local city and county building departments enforce Title 24 during permitting and inspections. The California Energy Commission writes and updates Part 6. The California Building Standards Commission oversees the broader code framework.

What is a Title 24 report?

A Title 24 report (CF1R for residential, PRF for nonresidential) certifies that a building’s design meets California’s energy efficiency standards. It is prepared by an energy consultant and submitted with building permit applications.

What are California’s 16 climate zones under Title 24?

California is divided into 16 climate zones, each with different energy budgets and performance standards. Coastal zones have milder requirements. Desert and mountain zones demand higher thermal performance from the building envelope.

Does Title 24 require solar panels?

Since the 2019 code cycle, all new low-rise residential buildings must include photovoltaic systems. The 2025 update expands this by requiring battery storage alongside solar for both residential and certain nonresidential projects.

How is Title 24 different from CALGreen?

Title 24 Part 6 sets mandatory energy code requirements. CALGreen (Part 11) covers broader green building standards, including water efficiency, material conservation, and indoor air quality, with both mandatory baselines and voluntary reach tiers.

Conclusion

Understanding what is Title 24 comes down to one thing: knowing what California expects from every building project before a permit gets approved.

The code touches insulation, HVAC efficiency, lighting power density, solar PV systems, and battery storage. It applies whether you are building a single-family home or a commercial warehouse.

Compliance paths exist for a reason. The prescriptive method keeps things simple. The performance method gives you design flexibility through energy modeling.

With the 2025 Building Energy Efficiency Standards now in effect, heat pump requirements and expanded vapor barrier considerations make early planning with a qualified energy consultant more important than before.

Check your climate zone. Pull the right compliance documents. And get your Title 24 report submitted before you expect that permit back.