What Is Title 24? California’s Energy Code Explained for Building Owners

Every commercial building project in California passes through Title 24, and almost every owner meets it for the first time as a plan check correction. The permit set comes back with comments referencing sections numbered 120.1, 140.4 and 141.0, a consultant asks which compliance path was assumed, and a schedule that looked settled starts to move. It is an avoidable experience, but only if the code is understood at the point where design decisions are made rather than at the point where they are reviewed.

This article explains what Title 24 is, what it governs, how compliance is demonstrated, and what changed in the code cycle that took effect at the start of 2026. It is written for owners, developers and project managers rather than for code officials, so the emphasis is on the decisions that cost money rather than on section by section recitation. Budlong has delivered MEP engineering services on California projects for decades, and much of what follows comes from watching where compliance goes wrong on real jobs. You can see the range of that work on our expertise overview.

1. What Is Title 24?

Title 24 is Part 24 of the California Code of Regulations. Its formal name is the California Building Standards Code, and it is the complete body of construction regulation that applies statewide. It is not a single document. It is a family of twelve numbered parts, each adopted and maintained by a different state agency under the coordination of the California Building Standards Commission.

Most of Title 24 consists of California amendments to model codes published nationally. The California Building Code is the International Building Code with state amendments, the California Mechanical Code is the Uniform Mechanical Code with state amendments, and the pattern repeats across electrical, plumbing and fire.

Part 6, the California Energy Code, is different. It is written from scratch by the California Energy Commission and has no national model equivalent. It is the most demanding energy code in the United States, it is revised on a three year cycle, and it is the part of Title 24 that consumes the majority of an engineering team’s compliance effort. When an architect says a project has a Title 24 problem, Part 6 is almost always what they mean.

2. How Title 24 Compliance Actually Works

Part 6 sets a performance target for a building and then offers two routes to prove that the target has been met. The choice between them shapes the entire design process, and it should be made in schematic design rather than after construction documents are underway.

The prescriptive path

The prescriptive path is a checklist. Every regulated component has a fixed minimum: envelope U values, glazing solar heat gain coefficients, equipment efficiencies, lighting power densities, control requirements and so on. Meet each one and the building complies. Nothing trades against anything else, so a superb mechanical system cannot offset an underperforming facade.

The prescriptive path is fast, cheap to document and appropriate for simple buildings with conventional systems: a single storey warehouse, a small tenant improvement, a straightforward retail shell. It becomes restrictive the moment architecture becomes ambitious.

The performance path

The performance path replaces the checklist with a simulation. Compliance software approved by the Energy Commission builds a hypothetical baseline building with the same geometry, orientation and occupancy as the proposed design but with every system set at the prescriptive minimum. The proposed design is then modelled against it. If the proposed building performs at or better than the baseline, it complies.

This is where trade offs become possible. A glazed facade that would fail prescriptively can be offset by high efficiency mechanical plant, better controls, a larger photovoltaic array or improved lighting design. The performance path is more work, requires energy modelling in MEP design, and is the default for anything with a meaningful architectural concept.

3. The Twelve Parts of Title 24

Understanding which part governs which question saves a great deal of time on any project. The table below maps the structure.

Two points are worth noting. Parts 3, 4 and 5 are installation codes while Part 6 is a performance code, so a design can satisfy one and fail the other. And Part 10 matters more than owners expect, because assuming an existing building is grandfathered is one of the more expensive mistakes made on adaptive reuse projects.

4. Which Projects Trigger Title 24 Part 6

New construction always triggers Part 6. The harder questions concern existing buildings, where the answer depends on what is being touched and how much of it.

New construction

Every newly conditioned building falls under the full scope of Part 6: envelope, mechanical, service water heating, indoor and outdoor lighting, power distribution, covered processes, and where applicable solar photovoltaics and battery storage.

Additions

An addition is generally treated as new construction for the added area. Where the addition affects existing systems, for example by loading an existing air handler or panel beyond its previous duty, the altered portion of the existing system is pulled into scope as well.

Alterations

Alterations are where judgement is required. Replacing a rooftop unit triggers requirements for that unit and often for the economizer and controls serving it. Replacing more than a defined proportion of luminaires in a space triggers the lighting control requirements for that space. Reconfiguring ductwork triggers duct sealing and leakage testing. The compliance triggers are cumulative, and a series of small permits over several years can quietly bring an entire floor into scope.

Change of occupancy

Converting an office floor to a medical suite, or a warehouse to a production facility, changes the ventilation, lighting and process requirements simultaneously. Change of occupancy projects are among the most commonly under scoped in early budgeting because the architectural work looks modest while the mechanical and electrical work is effectively new construction.

5. What Title 24 Asks of Each Building System

Part 6 is organised by system, and each has both mandatory measures that apply regardless of compliance path and prescriptive requirements that apply only if the prescriptive path is chosen.

Envelope

Insulation levels, fenestration U factor and solar heat gain coefficient, air leakage, cool roof requirements and, in the performance path, the interaction between glazing area and orientation. The envelope is fixed early and is expensive to revisit, which is why the compliance path decision needs to precede facade design rather than follow it.

Mechanical

Equipment efficiency minimums, economizer requirements, fan power limits, duct sealing and insulation, zoning, demand control ventilation and the minimum outdoor air calculation. The 2025 code introduces a revised minimum ventilation formula that takes the larger of an occupant based rate and an area based rate rather than defaulting to one method. It also expands the heat pump baseline that arrived in the 2022 cycle: multi zone systems in offices and schools below defined size thresholds now baseline to variable refrigerant flow heat pumps with dedicated outdoor air, four pipe fan coils with air to water heat pumps, or variable air volume systems with comparable equipment.

That single change has more effect on capital cost and plant room space than anything else in the 2025 cycle. It should be tested against the project budget during HVAC system selection, not discovered at plan check. Accurate HVAC load calculations matter more than ever, because heat pump plant is less forgiving of oversizing than the gas fired equipment it replaces.

Service water heating

Efficiency minimums, pipe insulation, recirculation controls and, increasingly, heat pump water heating baselines. Central domestic hot water plant in multifamily and hospitality buildings is one of the areas where the electrification trajectory of the code is clearest.

Lighting and power

Indoor and outdoor lighting power allowances, mandatory control requirements, daylighting controls, and receptacle controls. The 2025 code reduces the daylighting control trigger to 75 watts, restricts controlled segments to eight feet or less, eliminates the Tailored Method that many complex projects relied on, and limits sign illumination to LED and neon sources. Projects with architectural lighting design ambitions lost a useful compliance tool when the Tailored Method went, and the performance path now carries more of that load.

Solar photovoltaics and battery storage

The 2022 code extended the photovoltaic mandate well beyond housing into offices, retail, grocery, restaurants, schools, warehouses, hotels and high rise residential. The 2025 code updates the capacity factors used to size those systems, with restaurants seeing a notable increase, and adds battery energy storage requirements sized by formula. Early coordination between roof area, structural capacity, electrical service and photovoltaic design is now a code driven necessity rather than a sustainability preference.

6. CALGreen and the Rest of the Code Family

Part 6 gets the attention, but it is not the only part of Title 24 with sustainability content. Part 11, the California Green Building Standards Code or CALGreen, is mandatory statewide and covers ground that Part 6 does not.

CALGreen addresses water efficiency and conservation, material conservation and resource efficiency, construction waste diversion, and indoor environmental quality including low emitting materials and pollutant control during construction. Its mandatory measures apply to essentially all new nonresidential construction, with voluntary Tier 1 and Tier 2 measures available where a jurisdiction has adopted them or an owner elects them.

The interaction with Part 6 matters. CALGreen indoor air quality provisions influence ventilation design. CALGreen water efficiency provisions influence fixture selection and therefore plumbing design. Treating the two parts as separate workstreams produces conflicts that surface late.

Where LEED fits

LEED is voluntary, administered by the U.S. Green Building Council, and sits on top of the code rather than inside it. Because California’s code baseline is unusually high, projects pursuing LEED in California often earn energy points more readily than equivalent projects elsewhere. The efficient approach is to build one energy model that serves both the Part 6 compliance submission and the LEED energy performance credit, rather than commissioning two. That coordination is part of how we approach LEED MEP services and broader sustainable design services.

7. Healthcare, Laboratories and Data Centres

Three building types deserve separate treatment because their relationship with Part 6 is unusual.

Healthcare

Hospitals and skilled nursing facilities in California are regulated by the Department of Health Care Access and Information rather than the local building department, and their plan review follows a separate track. Part 6 still applies, but it interacts with ventilation and pressure relationship requirements that exist for infection control rather than energy reasons. Where the two conflict, patient safety governs, and the energy analysis has to be built around that constraint. Our healthcare facilities work covers acute care, outpatient and behavioural health environments where this tension is routine.

Laboratories

The 2025 code removed the laboratory exemption that had existed in previous cycles. Laboratories are now subject to energy code requirements, which is a significant change for research and life sciences developers who had planned around the exemption. High exhaust volumes, once through air and process loads that were previously outside the compliance envelope now have to be accounted for. Anyone with a lab project in design should confirm which cycle applies before assuming past precedent holds. This affects our laboratory and industrial clients directly.

Data centres and covered processes

Part 6 treats computer rooms as a covered process with its own efficiency and economizer requirements. As rack densities rise and liquid cooling enters the mainstream, the gap between what the code contemplates and what modern facilities actually deploy has widened. Projects in this space typically need the performance path and a careful conversation with the authority having jurisdiction. See our mission critical capability for context.

8. Choosing a Compliance Path

The compliance path decision should be made at the end of schematic design, once massing and glazing ratios are settled but before the facade is detailed. The table below sets out how the choice usually resolves.

The pattern we see most often is a project that starts prescriptive to save fee, hits a glazing or lighting constraint in design development, then switches to performance halfway through. That switch costs more than starting on the performance path would have, because the model must be built against a design never developed with modelling in mind.

9. Acceptance Testing and Field Verification

Compliance is not finished when the permit is issued. Part 6 requires that specified systems be tested in the field to confirm they operate as the compliance documents claim, and the certificate of occupancy depends on those tests passing.

What gets tested

Typical nonresidential acceptance tests cover outdoor air economizer operation, demand control ventilation, supply fan variable flow control, valve leakage, hydronic system controls, automatic daylighting controls, occupancy sensing controls and automatic shut off controls. Where a system has a control sequence, there is generally a test for it.

Who performs it

Acceptance testing must be carried out by a technician certified through an Acceptance Test Technician Certification Provider. Certification is system specific, so mechanical and lighting tests are usually performed by different people.

The documentation chain

Four document families carry the compliance record from design to occupancy. The Certificate of Compliance, or NRCC, is produced during design and submitted with the permit set. The Certificate of Installation, or NRCI, is signed by the installing contractor. The Certificate of Acceptance, or NRCA, records the field test results. The Certificate of Verification, or NRCV, covers third party field verification where required. Residential projects use CF1R, CF2R and CF3R in the equivalent roles.

Why it overlaps with commissioning

Acceptance testing and commissioning ask similar questions of the same equipment for different reasons. Acceptance testing asks whether the installation matches the code compliance submission. Commissioning asks whether the installation matches the owner’s requirements. Running them as separate exercises duplicates site visits and multiplies contractor disruption. Coordinating them through a single commissioning services scope is almost always cheaper, and the building commissioning process is built to absorb acceptance testing rather than run alongside it.

Key Takeaways

• Title 24 is the whole California Building Standards Code. Part 6 is the Energy Code and is what most compliance discussion refers to.
• The code edition in force on the permit application date governs. The 2025 Energy Code applies from 1 January 2026.
• Choose the compliance path at the end of schematic design. Switching later costs more than starting on the right path.
• The 2025 cycle expands heat pump baselines, adds battery storage alongside solar, rewrites the ventilation calculation, removes the laboratory exemption and eliminates the Tailored Method for lighting.
• Long Term System Cost has replaced Time Dependent Valuation as the compliance metric, which changes how savings are valued.
• Part 11 CALGreen is mandatory and sits alongside Part 6. Coordinate them rather than treating them separately.
• Acceptance testing is a permit condition, not a formality, and should be coordinated with commissioning.
• Existing buildings are not automatically exempt. Alteration triggers are cumulative and change of occupancy resets the analysis.

10. Where Budlong Works

Title 24 is a statewide code, but its practical application varies by jurisdiction. Plan check culture in Los Angeles is not the same as in San Francisco, local reach codes add requirements above the state baseline in many cities, and utility incentive programmes differ between service territories. Budlong maintains teams across California so that local plan check experience sits behind every submission. You can read more about how the practice is structured on our company story page.

Sectors where Title 24 bites hardest

Healthcare carries competing ventilation mandates. Education faces the new multi zone heat pump baseline directly. Multifamily and hospitality absorb central domestic hot water electrification pressure. Commercial buildings meet the photovoltaic and battery requirements first.

11. Related Reading

12. Frequently Asked Questions