California Title 24 Net Zero: Solar, Batteries, and Heat Pumps

California’s Title 24 net zero compliance rules tighten again on January 1, 2026, when the 2025 Building Energy Efficiency Standards take effect for every permit application filed on or after that date. In practical terms, a new single-family home must include a sized solar photovoltaic system, battery-ready wiring, a heat pump for space conditioning on the prescriptive path, and documented verification by an independent HERS rater. New non-residential buildings face similar solar and efficiency rules plus, in many cases, an actual installed battery. Projects already permitted under the 2022 code can still be built to those older standards.¹

The code sits inside Title 24, Part 6, of the California Code of Regulations and is updated by the California Energy Commission on a roughly three-year cycle. The underlying policy goal, set in the state’s Energy Efficiency Strategic Plan, is zero net energy: all new residential construction was targeted to reach ZNE by 2020, and all new commercial construction by 2030. A zero-net-energy building generates at least as much renewable energy on-site each year as it uses.² The 2025 code is the current step toward that commercial target, and the CEC estimates its updates will save Californians about $4.8 billion in energy costs over 30 years and cut greenhouse gas emissions by roughly 4 million metric tons.³

Solar PV on New Homes

Every new single-family home and low-rise multifamily building has to include a solar PV system. The required size is the smaller of two numbers: one calculated from the building’s solar access roof area (SARA), and one from a formula based on climate zone, conditioned floor area, and number of dwelling units.⁴

The SARA calculation multiplies usable roof area by 18 watts per square foot for steep-sloped roofs or 14 watts per square foot for low-sloped roofs. Roof sections facing roughly north (between 300 and 90 degrees from true north) are excluded from steep-sloped calculations because they produce little useful energy. Climate zone matters on the formula side because hotter areas need more cooling, and California has 16 climate zones; a Central Valley home needs a larger system than the same floor plan on the mild coast.

When Solar Isn’t Required

The code recognizes that not every lot works for rooftop solar. A PV system is not required at all when the formula produces a size below 1.8 kW DC, or when the available SARA is less than 80 contiguous square feet. If objects outside the builder’s control, such as neighboring buildings or large trees, shade the roof so that no area receives at least 70 percent of available solar energy, no solar zone is required. Shading claims have to be backed by a solar access analysis in the project documents.⁴

Pairing the PV with a battery of at least 7.5 kWh of cycling capacity reduces the required PV size by 25 percent. A CEC-approved community shared solar system or community shared battery storage system can also partially or fully substitute for the on-site requirements that would otherwise apply to residential and non-residential buildings.⁵ That matters most for projects where rooftop solar is impractical but the project doesn’t qualify for a full exemption.

Battery Storage Requirements

The 2025 code splits battery rules between residential and non-residential buildings. Homes have to be ready for a battery. Many commercial projects have to install one.

Battery-Ready Wiring for Homes

New single-family buildings with one or two dwelling units and electrical service above 125 amps must include battery-ready infrastructure. The main panel needs a minimum 225-amp busbar rating. The home needs either BESS-ready interconnection equipment with at least 60 amps of backed-up capacity or a dedicated one-inch raceway from the main service panel to a subpanel for future battery circuits. At least four branch circuits must be configured to be fed by the future battery, covering a refrigerator, lighting near the primary exit, and a sleeping room outlet. A reserved area within three feet of the main panel must be kept clear for future system isolation equipment.⁶

These requirements apply only to new construction. Additions and alterations are exempt, as are buildings that already have a battery installed.⁶

Installed Batteries for Non-Residential Buildings

Many non-residential buildings must actually install a battery energy storage system. Its rated energy capacity is calculated from the building’s conditioned floor area, its required PV size, the battery’s round-trip efficiency, and a capacity factor that varies by building type.⁷

The battery itself has to clear performance minimums: round-trip efficiency greater than 80 percent and a warranty guaranteeing at least 70 percent of nameplate capacity after either 4,000 cycles or 10 years. Three exceptions can eliminate the requirement: the installed PV system is less than 15 percent of the calculated required capacity, the calculated battery capacity falls below 10 kWh, or the building is a single-tenant space under 5,000 square feet of conditioned floor area. In multi-tenant buildings, the battery is sized only against tenant spaces exceeding 5,000 square feet.⁷

Heat Pumps and the Shift Away From Gas

Gas-fired space conditioning is effectively off the prescriptive path for new single-family homes under the 2025 code. If a project wants the simpler prescriptive route, the heating and cooling system has to be a heat pump. Gas furnaces and boilers can still appear in a design, but only through the performance path, where the designer uses energy modeling to show the overall building energy budget still meets the standard. This is a meaningful tightening from the 2022 code, which allowed gas equipment prescriptively in more situations.

Water heating moves the same direction. The 2025 code adds mandatory requirements for heat pump water heater installations, including backup heat provisions when inlet air is unconditioned, minimum space volumes around the unit based on compressor capacity, and specific ventilation configurations for ducted and non-ducted setups. Heat pump water heaters pull warmth from surrounding air, so they need adequate airflow to operate at rated efficiency.

Even where gas equipment is still allowed through the performance path, the building must include electric-readiness infrastructure so the owner can switch to electric systems later without a costly retrofit.

Non-Residential Buildings

Commercial buildings, offices, retail spaces, and high-rise residential buildings of four or more stories fall under the non-residential standards. Solar PV sizing uses either a conditioned floor area method or the solar access roof area method, whichever the designer selects. Lighting rules require automatic daylighting controls that dim or switch off electric lights when natural light is sufficient. Mechanical systems have to meet ventilation rates calculated from both occupancy levels and floor area. Combined with the battery rules above, these provisions are how the code moves non-residential construction toward the 2030 ZNE target.²

Prescriptive vs. Performance Compliance

Every project demonstrates compliance through one of two routes. The prescriptive path is a checklist: specific insulation R-values, equipment efficiency ratings, required solar sizes, and mandatory features. If every component meets or exceeds the listed specifications, the project complies without any modeling. It works well for standard designs.

The performance path uses approved energy modeling software to compare the proposed building against a baseline building that just barely meets the prescriptive standards. If the proposed design performs equal to or better than the baseline, it complies. Designers can trade off components: more insulation and better windows might allow a smaller solar array because the overall energy budget still works.

One useful detail for projects with constrained roof area: adding a battery storage system can generate a self-utilization credit on the performance path, potentially reducing required solar PV size beyond the 25 percent prescriptive reduction.⁴ Combined with the battery, the performance path is often the only workable route for tight sites.

Documentation and HERS Verification

Compliance runs on three certificates, each registered with an approved Energy Code Compliance data registry and submitted to the local building department.⁸

The CF-1R, or Certificate of Compliance, is the design document. The building designer signs it before construction to certify the plans meet the code.
The CF-2R, or Certificate of Installation, is signed by the installer to confirm the specified equipment and materials were installed correctly.
The CF-3R, or Certificate of Verification, is signed by a certified HERS rater after independent diagnostic testing.

HERS raters are independent third parties. They cannot be employees of the builder or contractor and cannot have a financial interest in the project they test. Testing is triggered by specific efficiency measures in the design, so not every home gets the same battery of tests. Common items include duct sealing and leakage, refrigerant charge in air conditioning and heat pump systems, building envelope air leakage, insulation quality, mechanical ventilation airflow, and solar PV system performance.

Before testing, the rater confirms the CF-1R and CF-2R have already been transmitted to the registry and that the installation certificates match the approved compliance documents. If testing confirms compliance, the registry generates the registered CF-3R, and a copy has to be posted at the building site for the final inspection. If testing turns up problems, the builder has to correct them and schedule a retest. For larger developments, a sampling procedure can replace unit-by-unit testing, provided the units are the same type and built by the same subcontractor.

Additions, Alterations, and ADUs

Title 24 doesn’t apply only to new buildings. An addition, which is any change that increases conditioned floor area or volume (including converting a garage to living space), has to meet the energy code for the new portion through a certificate of compliance. An alteration is any change to the envelope, space conditioning, water heating, or lighting systems that isn’t an addition. Replacing a furnace, swapping a condensing unit, or installing more than 40 linear feet of new ductwork all count. Only the altered components must meet current standards; you don’t have to bring the whole existing building up to the latest code.⁹

Pure maintenance repairs sit outside the energy standards, but replacing any component with code requirements counts as an alteration, not a repair, regardless of why you’re replacing it. Swap a broken water heater and you’re doing an alteration.

Accessory dwelling units are treated as residential buildings. A newly built detached ADU needs its own PV system meeting the prescriptive requirements unless an exemption applies. New modules can be added to an existing rooftop system on the same lot to satisfy the requirement, as long as the added modules are in the ADU’s permit application and sized per the code.¹⁰ If an existing unpermitted ADU is being legalized, the building department decides whether it must comply as new construction or as an addition. Current energy code applies either way.

Federal Tax Credits That Offset the Equipment

The federal Residential Clean Energy Credit helps cover the solar and battery hardware the state now requires. It covers 30 percent of the cost of qualifying clean energy property, including solar electric panels, battery storage with at least 3 kWh of capacity, and installation labor. The credit is nonrefundable but carries forward to future tax years, and there is no annual or lifetime dollar cap. You can claim it for a primary home or a second home you live in part-time, but not for rental property where you don’t live. Business use of 20 percent or less still gets the full credit; above that threshold, the credit applies only to the personal-use share of expenses. Rebates and utility incentives have to be subtracted from qualified expenses before calculating the credit.¹¹

Commercial owners have a separate incentive under Section 179D, a per-square-foot deduction for energy-efficient buildings. For 2025, the deduction ranges from $0.58 to $5.81 per square foot depending on the level of energy savings and whether the project meets prevailing wage and apprenticeship requirements. It does not apply to property whose construction begins after June 30, 2026.¹²

What Happens If You Don’t Comply

Title 24 is enforced through the building permit process. A project that doesn’t produce the required certificates will not pass inspection, and the local building department can refuse to issue a certificate of occupancy. That means no legal move-in, no opening for business.

Administrative fines for building code violations in California run up to $100 for a first violation, $500 for a second violation of the same code within a year, and $1,000 for each additional violation within a year. The fines are modest next to the real cost: retrofitting a finished building to add insulation, upgrade equipment, or install solar is far more expensive than building it right the first time. Duct systems buried behind drywall cannot be sealed without opening walls. A heat pump water heater that should have been planned into the mechanical room during design may not fit after construction. Carrying costs on a building you cannot occupy run on top of all of it.

1
California Energy Commission. 2025 Building Energy Efficiency Standards
2
California Public Utilities Commission. Zero Net Energy
3
California Energy Commission. California’s Energy Code Update Guides the Construction of Cleaner, Healthier Buildings
4
California Energy Commission. 2025 Single-Family Solar PV
5
Energy Code Ace. 10-115 Community Shared Solar Electric Generation System
6
California Energy Commission. 2025 Single-Family Battery Energy Storage System (BESS) Ready
7
California Energy Commission. 2025 Nonresidential Battery Energy Storage System (BESS)
8
California Energy Commission. 2025 Energy Code Compliance Documents – Forms for Single-Family Buildings
9
California Energy Commission. Chapter 9 – Additions, Alterations, and Repairs
10
California Energy Commission. 2022 Energy Code Accessory Dwelling Units (ADU) FAQs
11
Internal Revenue Service. Residential Clean Energy Credit
12
Department of Energy. 179D Energy Efficient Commercial Buildings Tax Deduction