What Is Title 24 in California? Parts, Climate Zones, Compliance

Title 24 of the California Code of Regulations is the state’s Building Standards Code, a set of twelve regulatory parts that govern how every building in California is designed, constructed, and renovated. The California Building Standards Commission publishes and maintains it, and the full code is updated on a three-year cycle to fold in new technology and safety research.¹ The current 2025 edition took effect January 1, 2026, so any permit application submitted on or after that date must meet the latest standards.²

If you are building, remodeling, adding square footage, or even swapping out a water heater, Title 24 is the rulebook your local building department will check your work against before it signs off.

The Twelve Parts of Title 24

Title 24 is organized into twelve numbered parts, each covering a different technical discipline. The Building Standards Commission lists them as follows:¹

Part 1 — Administrative Code: procedural rules for how all other parts are applied and enforced.
Part 2 — California Building Code: structural requirements, based on the International Building Code.
Part 2.5 — California Residential Code: standards specific to one- and two-family dwellings.
Part 3 — California Electrical Code: wiring, panels, and electrical systems, based on the National Electrical Code.
Part 4 — California Mechanical Code: HVAC, ventilation, and exhaust systems.
Part 5 — California Plumbing Code: water supply, drainage, and fixtures.
Part 6 — California Energy Code: energy performance of the building envelope, lighting, and mechanical systems.
Part 7 — California Wildland-Urban Interface Code: construction standards for buildings in fire-prone areas.
Part 8 — California Historical Building Code: alternative standards for qualified historic structures.
Part 9 — California Fire Code: fire and life safety, sprinklers, exits, and alarms.
Part 10 — California Existing Building Code: rules for repairing, altering, or adding to existing structures.
Part 11 — California Green Building Standards Code (CALGreen): water conservation, construction waste diversion, and EV charging infrastructure.
Part 12 — California Referenced Standards Code: industry standards incorporated by reference throughout the other parts.

Most homeowners and small builders deal most directly with Parts 2, 6, and 11, because those three generate the bulk of the documentation and inspections tied to a permit. Parts 3 through 5 are usually handled by the licensed trades, whose work is inspected separately. Every part carries equal legal weight, though, and the building department checks compliance across the entire code before granting final approval.

Which Projects Have to Comply

Every new building constructed in California must meet the current edition of Title 24, whether it is a single-family home, a commercial office, or a warehouse. The reach does not stop at ground-up construction. The code also applies to:

Additions. New square footage added to an existing building must meet current standards for the added area.
Alterations. Replacing windows, upgrading a water heater, installing a new HVAC system, or remodeling a kitchen or bathroom can trigger Energy Code compliance for the components being changed.
Accessory dwelling units. All ADUs, whether detached, attached, or converted from a garage, must comply with the Energy Code regardless of the unit’s size. There is no small-project exemption, and mandatory lighting and ventilation requirements apply to every newly constructed dwelling unit no matter how small.³

The scope catches more projects than most people expect. Swapping out a furnace or replacing a handful of windows does not feel like a construction project, but both typically require a permit and a Title 24 compliance document for the affected components.

The Energy Code (Part 6) in Plain Terms

Part 6 is the section that generates the most paperwork. It sets performance targets for three things: the building envelope, the lighting, and the mechanical systems. The California Energy Commission administers it separately from the Building Standards Commission.⁴

The envelope rules dictate how well a building retains conditioned air. Walls and attics must meet minimum insulation R-values that vary by climate zone. Windows must hit specific U-factor and Solar Heat Gain Coefficient targets to limit heat transfer through glass. Roofs on most building types must use cool-roof materials with high solar reflectance. These rules interact: better windows can sometimes offset thinner wall insulation, and compliance software accounts for the tradeoffs automatically.

On the lighting side, indoor and outdoor fixtures must stay within maximum power-density limits, which in practice means high-efficacy LEDs and automatic shut-off controls like occupancy sensors. HVAC equipment must meet minimum efficiency ratings, and ductwork must be sealed and insulated. Water heaters face their own efficiency thresholds, and hot-water piping often requires insulation and recirculating pump controls. The 2025 Energy Code expands the use of heat pumps in new residential construction and encourages electric-ready infrastructure so buildings can transition away from gas appliances later.²

Climate Zones Change the Rules

California is divided into sixteen climate zones, and the Energy Code adjusts its requirements based on where your project sits on that map.⁵ A home in foggy San Francisco (Climate Zone 3) faces different insulation and window requirements than one in the desert around Palm Springs (Climate Zone 15). Envelope and fenestration standards are especially zone-dependent: a window U-factor that passes in a mild coastal zone may fail in an inland valley where summer temperatures regularly exceed 100°F.

Compliance software asks for the project’s climate zone early and calculates every subsequent energy budget from it. Getting the zone wrong cascades through the whole report, so verify your zone using the Energy Commission’s online lookup tool before any modeling begins.

Solar, Battery, and Green Building Rules

Starting with the 2020 code cycle and expanded in 2025, a solar photovoltaic system is prescriptively required on all newly constructed buildings. When a project qualifies for an exception and skips the panels, it must still meet mandatory solar-ready requirements so the roof and electrical system can accommodate a future installation.⁶ Single-family homes, duplexes, triplexes, and low-rise multifamily buildings up to three stories all fall under the mandate.

Battery energy storage is not yet mandatory for most residential projects, but the 2025 code requires newly constructed single-family homes that skip battery installation to include battery-ready infrastructure so a system can be added later without rewiring.⁶

CALGreen (Part 11) covers territory Part 6 does not. It addresses water-efficient landscaping, construction waste diversion that requires a percentage of demolition debris be recycled rather than landfilled, indoor air quality measures like low-emitting adhesives and paints, and EV charging infrastructure for new residential and commercial parking areas.⁴ CALGreen also includes voluntary Tier 1 and Tier 2 provisions that some local jurisdictions adopt as mandatory, so check with your city or county to see whether they have raised the baseline.

What You Have to Submit and Verify

Before a local building department issues a permit for work that triggers the Energy Code, the applicant must submit a Certificate of Compliance. For single-family residential projects, this is the CF1R form.⁷ The CF1R captures the technical specifications of the proposed design: insulation R-values, window U-factors and Solar Heat Gain Coefficients, HVAC equipment ratings, and water heating details. Every data field must match the construction plans, because the inspector will check both documents against each other.

For performance-based compliance, generating a CF1R requires running the design through energy modeling software approved by the Energy Commission.⁸ Many property owners hire a Title 24 energy consultant to run these calculations. Professional fees for a straightforward single-family project generally fall in the $200 to $500 range, with complex or commercial designs costing more. Prescriptive compliance for simple alterations can sometimes be documented using fillable PDF forms from the Energy Commission’s website without modeling software.

Once construction is underway, certain installations must be verified on site before the building department grants final approval. A certified Home Energy Rating System (HERS) rater typically handles this. HERS raters are qualified to verify the work of licensed HVAC contractors and inspect a home’s equipment, air ducts, vents, and thermostat settings.⁹ Common tests include duct leakage measurements, airflow verification, refrigerant charge checks, building air leakage tests, and quality insulation installation inspections.⁷

This is where projects stall more often than people expect. A duct system that leaks beyond the allowed threshold or an HVAC unit with improper airflow will fail verification, and no amount of paperwork fixes a physical installation problem. Schedule the HERS rater early enough that you have time to correct issues before your final inspection date.

What Happens If You Don’t Comply

Local building departments are the primary enforcement arm for Title 24. A project that fails to demonstrate compliance can face a stop-work order, meaning construction halts until the violation is corrected. The inspector must provide written notice specifying which code section was violated and why the work does not conform to approved plans.¹⁰

Contractors who perform work without the required building permit face disciplinary action from the Contractors State License Board, including civil penalties of up to $5,000 per violation and potential suspension or revocation of their license.¹¹ For property owners, unpermitted or non-compliant work often surfaces during a home sale when a buyer’s inspector or appraiser flags the discrepancy, creating costly delays and sometimes requiring the work to be torn out and redone to current code.

The Three-Year Update Cycle and Why Permit Timing Matters

The Building Standards Commission updates Title 24 every three years, incorporating new model codes from organizations like the International Code Council and updated editions of the National Electrical Code. The current 2025 edition took effect January 1, 2026, and the 2028 edition is expected to take effect on January 1, 2029.¹²

The applicable code is determined by your permit application date, not your construction start date. Submit a permit application in December before a new code takes effect, and you comply with the outgoing edition. Submit in January, and you are on the new one. For large projects where new requirements would significantly change the design, that calendar awareness can save real money.

1
California Department of General Services. Codes
2
California Energy Commission. 2025 Building Energy Efficiency Standards
3
California Energy Commission. 2025 Energy Code Accessory Dwelling Units (ADU) FAQs
4
California Energy Commission. Building Energy Efficiency Standards
5
California Energy Commission. Climate Zone Tool, Maps, and Information Supporting the California Energy Code
6
California Energy Commission. Solar PV, Solar Ready, Battery Energy Storage System (BESS)
7
California Energy Commission. 2025 Energy Code Compliance Documents – Forms for Single-Family Buildings
8
California Energy Commission. 2025 Energy Code Compliance Software
9
California Energy Commission. Home Energy Rating System Program – HERS
10
California Legislative Information. California Health and Safety Code HSC 18941
11
Contractors State License Board. Building Permit Complaint
12
California Department of General Services. 2027 Triennial Code Adoption Cycle