To comply with California’s Title 24 net zero push, any building permit application filed on or after January 1, 2026 must meet the 2025 Building Energy Efficiency Standards under Title 24, Part 6 of the California Code of Regulations.1California Energy Commission. 2025 Building Energy Efficiency Standards For most new homes that means a rooftop solar system, battery-ready wiring, and heat pump equipment for space and water heating. Non-residential projects face solar plus an actual installed battery, along with tighter efficiency requirements. Projects already permitted under the 2022 code can still be built to those older standards. The whole framework is designed to move California toward its goal that all new commercial construction reach zero net energy by 2030.2California Public Utilities Commission. Zero Net Energy
A zero-net-energy building produces at least as much renewable energy on-site each year as it consumes. Title 24 doesn’t hit that number in a single code cycle. It ratchets closer every three years, and 2025 is the tightest cycle yet.
Solar PV Requirements for New Homes
Every new single-family home and low-rise multifamily building must include a solar photovoltaic system. The required size is the smaller of two calculations: one based on the building’s solar access roof area (SARA), and one based on a formula tied to climate zone, conditioned floor area, and number of dwelling units.3California Energy Commission. 2025 Single-Family Solar PV
The SARA method uses the roof area that actually gets sun. Steep-sloped roofs are multiplied by 18 watts per square foot; low-sloped roofs by 14 watts per square foot. Roof areas facing roughly north (between 300 and 90 degrees from true north) drop out of the steep-sloped calculation because they produce little useful energy. Climate zone drives the second calculation because hotter zones need more cooling energy, and therefore more on-site generation to offset it. California has 16 climate zones, and a Central Valley home will need a bigger array than an identical home on the coast.
Exemptions and Reductions
Not every home ends up with panels. Several outs exist:
- If the formula produces a required size below 1.8 kW DC, no PV system is required.
- If available SARA is less than 80 contiguous square feet, the requirement is waived.
- If objects outside the builder’s control (neighboring buildings, large trees) shade the roof so that no area receives at least 70 percent of available solar energy, no solar zone is required.
- Installing a battery energy storage system with at least 7.5 kWh of cycling capacity reduces the required PV size by 25 percent.
The shading and small-system exemptions are where most exceptions actually come into play. Builders claiming a shading exemption need to document the solar access analysis.3California Energy Commission. 2025 Single-Family Solar PV
If approved by the CEC, a community shared solar system or community shared battery storage system can partially or fully substitute for on-site solar and battery requirements that would otherwise apply.4Energy Code Ace. 10-115 Community Shared Solar Electric Generation System This matters most for projects where rooftop solar is impractical but no full exemption applies.
Battery Storage: Ready vs. Installed
Single-Family Homes: Battery-Ready Wiring
The 2025 code does not require homebuilders to install a battery. It requires them to make the home ready for one. New single-family buildings with one or two dwelling units, where electrical service exceeds 125 amps, must include battery-ready infrastructure.5California Energy Commission. 2025 Single-Family Battery Energy Storage System (BESS) Ready In practice, that means:
- A main panel with a minimum 225-amp busbar rating.
- 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 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 for future system isolation equipment.
These requirements apply only to new construction. Additions and alterations are exempt, and so are buildings that already have a battery system installed.
Non-Residential: Install a Battery
Commercial projects face a stiffer rule. Many must actually install a battery energy storage system, not just wire for one. Rated energy capacity is calculated using formulas based on the building’s conditioned floor area, its required PV system size, the battery’s round-trip efficiency, and a capacity factor that varies by building type.6California Energy Commission. 2025 Nonresidential Battery Energy Storage System (BESS)
The battery must exceed 80 percent round-trip efficiency and carry a warranty guaranteeing at least 70 percent of nameplate capacity after 4,000 cycles or 10 years. Three exceptions can eliminate the battery requirement:
- The installed PV system is less than 15 percent of the calculated required capacity.
- The calculated battery capacity comes out below 10 kWh.
- The building is a single-tenant space under 5,000 square feet of conditioned floor area.
For multi-tenant buildings, the battery is sized only against tenant spaces exceeding 5,000 square feet.
Heat Pumps and Electric-Readiness
The 2025 code effectively removes gas-fired space conditioning from the prescriptive compliance path for new single-family homes. If you want the simpler prescriptive route, the system has to be a heat pump. Gas furnaces and boilers can still appear in a project, but only if the designer uses the performance path and shows the overall building energy budget still meets the standard. That is a real tightening from the 2022 code, which allowed gas equipment prescriptively in more situations.
Water heating follows the same track. The 2025 code lays out detailed 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 installations. Heat pump water heaters pull warmth from surrounding air, so they need adequate airflow to operate efficiently.
Even where gas equipment is still installed through the performance path, electric-readiness provisions require infrastructure to support a future switch to electric systems. The idea is to head off costly retrofits when aging gas equipment is eventually replaced.
Choosing a Compliance Path
Every project must demonstrate compliance through one of two routes.
The prescriptive path is a checklist: specific insulation R-values, particular equipment efficiency ratings, required solar system sizes, mandatory features. Meet or exceed each listed specification and the project complies. No modeling required. It works well for standard designs.
The performance path offers flexibility. Using approved energy modeling software, the designer builds a virtual version of the proposed building and compares its projected energy use to a baseline building that just barely meets the prescriptive standards. As long as the proposed design performs equal to or better than the baseline, it complies. That lets designers trade off between components. A building with more insulation and better windows can sometimes get away with a smaller solar array because the overall energy budget still balances.
One advantage of the performance path is often overlooked: adding a battery storage system can generate a self-utilization credit against the energy efficiency requirement, potentially cutting required solar PV size beyond the 25 percent prescriptive reduction.3California Energy Commission. 2025 Single-Family Solar PV For projects with constrained roof area, performance path plus battery is often the only practical route to compliance.
Documentation and HERS Verification
Compliance runs on three certificates. Each must be registered with an approved Energy Code Compliance data registry and submitted to the local building department.7California Energy Commission. 2025 Energy Code Compliance Documents – Forms for Single-Family Buildings
- CF-1R, the Certificate of Compliance, is the design document. The building designer signs it to certify the plans meet the energy code before construction begins.
- CF-2R, the Certificate of Installation, is the construction document. The installer signs it to confirm the specified equipment and materials went in correctly.
- CF-3R, the Certificate of Verification, is the testing document. A certified HERS rater performs independent diagnostic testing and signs it to verify the building performs as designed.
HERS raters are independent third-party inspectors. They cannot be employees of the builder or contractor, and they cannot have a financial interest in the project they’re testing. Their job is to verify that what’s actually built matches what’s on paper.
Testing only kicks in when the project includes specific efficiency measures, so not every home gets the same battery of tests. Common triggers 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. The full list runs to over 30 potential test categories.
Before testing, the rater confirms that the CF-1R and CF-2R have already been transmitted to the registry and that the installation certificates are consistent with the approved compliance documents. If testing confirms compliance, the rater transmits results to the registry, which generates the registered CF-3R. A copy must be posted at the building site for the final inspection. If testing reveals problems, the builder corrects them and schedules a retest. For larger developments, builders can use a sampling procedure instead of testing every individual unit, provided the units are the same type and built by the same subcontractor.
Additions, Alterations, and ADUs
The energy code doesn’t apply only to new construction. An addition is any change that increases conditioned floor area or volume, including converting a previously unconditioned space like a garage into living space. Additions must meet the energy code for the new portion of the building, and the designer must complete a certificate of compliance using either the prescriptive or performance approach.8California Energy Commission. Chapter 9 – Additions, Alterations, and Repairs
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 qualify and trigger specific compliance requirements. Only the altered components need to meet current standards; the rest of the existing building does not have to be brought up to code.
Repairs done purely for maintenance are outside the scope of the energy standards. But note the catch: replacing any component that has requirements in the energy code is classified as an alteration, not a repair, regardless of why you’re replacing it. Swapping a broken water heater for a new one is an alteration.
ADUs are subject to the energy code like any other residential building. A newly constructed detached ADU must have its own solar PV system meeting the prescriptive requirements unless an exemption applies. New PV modules can be added to an existing rooftop system on the same lot to satisfy this, as long as the added modules are included in the ADU’s permit application and sized per the code.9California Energy Commission. 2022 Energy Code Accessory Dwelling Units (ADU) FAQs If an existing unpermitted ADU is being legalized through a new permit, the building department decides whether it must comply as new construction or as an addition. Either way, current energy code requirements apply.
Federal Tax Credits That Offset the Cost
The federal Residential Clean Energy Credit helps cover the solar and battery equipment Title 24 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 labor costs for installation.10Internal Revenue Service. Residential Clean Energy Credit
The credit is nonrefundable, so it reduces your tax bill but can’t produce a refund on its own. Unused credit carries forward. 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 properties where you don’t live. If your home has business use of 20 percent or less, you still get the full credit; above 20 percent, the credit applies only to the personal-use share of expenses. Rebates, utility incentives, and similar subsidies must be subtracted from your qualified expenses before calculating the credit.
Commercial building owners have a separate incentive under Section 179D, which provides 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.11Department of Energy. 179D Energy Efficient Commercial Buildings Tax Deduction Section 179D does not apply to property whose construction begins after June 30, 2026, so commercial developers should plan around that cutoff.
What Happens If You Don’t Comply
The energy code is enforced through the building permit process. A project that doesn’t demonstrate compliance through the required certificates won’t pass inspection. The local building department can refuse to issue a certificate of occupancy until the requirements are met, which means you can’t legally move in or open for business.
Retrofitting is where the real cost sits. Adding insulation, upgrading equipment, or installing solar panels after the fact costs substantially more than building it right the first time. Duct systems buried behind drywall can’t be sealed without opening walls. A heat pump water heater that should have been planned into the mechanical room may not fit after construction.
Administrative fines for building code violations in California follow a tiered structure: 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. Those fines are small next to the cost of tearing out and redoing non-compliant work, plus the carrying costs on a building you can’t occupy while the problems get fixed.