California’s 2025 Energy Code requires prescriptive solar PV on most newly constructed single-family homes, qualifying multifamily buildings, and many nonresidential projects, with the rule taking hold for any permit application submitted on or after January 1, 2026. Buildings that qualify for an exception still must include solar-ready and, in some cases, battery-ready infrastructure. The California Energy Commission oversees these standards, while the California Public Utilities Commission governs how a completed system gets connected and billed.

TL;DR:

  • For nonresidential projects, a listed occupancy must cover at least 80% of conditioned floor area before the mandate applies to the whole building.
  • Even when an exception removes the PV installation requirement, plans still need a reserved solar zone, conduit paths, inverter and meter locations, and panel capacity.
  • A qualifying battery with 7.5 kWh of usable capacity cuts required PV size by 25% and satisfies battery ready rules; homes above 125 amps otherwise need readiness.
  • Use the smaller result from floor area calculations or roof multipliers: 18 watts per square foot for steep roofs, 14 for low slope roofs.
  • Compliance follows permit submission, not construction start; applications filed from January 1, 2026, require updated forms, while early utility interconnection affects tariff eligibility.
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Table of Contents

What the mandate requires by building type

Whether your project needs installed solar PV, battery storage, or just the infrastructure to add them later depends heavily on what you’re building. We’ve found that most confusion on job sites traces back to builders assuming one set of rules covers every structure type, when the code actually treats single-family homes, multifamily buildings, and nonresidential projects differently.

For single-family homes, prescriptive PV is required unless a project qualifies for one of the exceptions covered below. Homes with a main electrical service panel rated above 125 amps also need to be battery-ready, meaning the panel and wiring must accommodate a future battery energy storage system even if one isn’t installed at construction. Adding an actual BESS at the time of construction can reduce the required PV system size, a tradeoff we detail further on.

Multifamily buildings are evaluated differently depending on height and configuration. High-rise and multi-tenant buildings have their own PV triggers under the 2025 Energy Code, and mixed-use buildings get assessed based on how much of the structure’s floor area is residential versus commercial.

Nonresidential projects follow Table 140.10-A, which lists specific occupancy categories (offices, retail, hotels, and similar uses) that trigger the requirement. A key detail here: coverage applies once the triggering occupancy type makes up at least 80% of the building’s conditioned floor area, which determines whether the whole project falls under the mandate or only a portion of it.

Exceptions and solar-ready requirements you still have to meet

Not every new building needs panels on the roof, but almost every building still needs to be prepared for them. The 2025 Energy Code’s express terms lay out five primary exceptions for single-family homes, and a parallel set applies to nonresidential projects.

  1. The solar access roof area is too limited, generally under 80 contiguous square feet or oriented toward unfavorable northerly azimuths.
  2. The calculated PV system would fall below the minimum size threshold for single-family homes.
  3. Structural limitations tied to ASCE 7 snow-load requirements make installation impractical.
  4. The project received local approval before January 1, 2020, under a prior code cycle.
  5. A qualifying battery energy storage system is installed, which can reduce the required PV size by 25%.

Even when one of these applies, the construction documents still need to show a reserved solar zone, identified inverter and meter locations, and conduit or raceway pathways for a future system. Panels must leave minimum busbar capacity and reserved breaker space so a system can be added without re-wiring the service panel later. Subdivisions and additions that expand conditioned floor area can also trigger these solar-ready obligations, even when the addition itself wouldn’t independently require PV.

Pro Tip: Label the reserved solar zone and conduit pathway directly on your electrical plan sheet, not just in a separate notes section. Plan reviewers look for it there first.

Battery storage requirements and when BESS-ready is enough

Battery storage isn’t required on every project, but where it applies, the distinction between an installed system and a battery-ready one matters for both your electrical plans and your budget conversations with an electrician.

A home with main service above 125 amps needs battery-ready infrastructure, meaning the panel, raceway, and branch circuits are sized and positioned for a future BESS, even if no battery ships with the project. If you install an actual battery that meets the qualifying threshold, which the code sets at a minimum of 7.5 kWh of usable capacity, you can reduce your required PV system size by 25% under the exception described above. Installing a qualifying BESS at construction also means you don’t need to separately meet the battery-ready provisions, since the system itself satisfies the intent of that requirement.

Nonresidential buildings calculate battery capacity differently. Energy capacity scales with conditioned floor area, and required power capacity is based on a four-hour charge and discharge cycle, a method the Energy Commission’s nonresidential guidance spells out for compliance software.

How required PV system size gets calculated

Sizing the required PV system comes down to comparing two numbers and installing whichever is smaller. The first method uses Equation 150.1-C (or 140.10-A for nonresidential projects), which bases the requirement on conditioned floor area. The second method uses your solar access roof area, commonly called SARA, which is the portion of your roof genuinely available for panels once you’ve accounted for shading, orientation, and obstructions.

The 2025 Energy Code sets SARA multipliers at 18 watts per square foot for steep-sloped roofs and 14 watts per square foot for low-sloped roofs. Those multipliers determine how much PV capacity your available roof area can theoretically support, and that figure gets compared directly against the floor-area-based equation.

A CEC-certified solar assessment tool makes calculating SARA far more reliable than estimating it by eye, especially on lots with mature trees or neighboring structures that cast shade.

Small systems are exempt from the requirement entirely: single-family projects calculating below roughly 1.8 kWdc and nonresidential projects below a minimum size threshold.

Permitting and compliance: forms, timing, and who checks your work

The compliance trigger is the date your permit application gets submitted, not your construction start date. Any project with a permit application filed on or after January 1, 2026 falls under the 2025 Energy Code and must use the updated compliance software and forms rather than the prior cycle’s documentation.

  1. Confirm your local building department is accepting 2025 Energy Code compliance software before you finalize plan sets, since older NRCC/NRCI forms won’t satisfy the new requirements.
  2. Submit the appropriate certificates for your scope, including solar-ready documentation (often an NRCC-SRA-E certificate) even when an exception removes the PV installation requirement itself.
  3. If you’re installing PV or BESS, prepare the matching installation certificates that document system size, battery capacity, and electrical configuration for the enforcement agency’s review.
  4. Coordinate with your plan reviewer early, since enforcement agencies increasingly expect solar-ready zones, conduit pathways, and reserved breaker space to be clearly called out on the electrical sheet rather than buried in general notes.
  5. Start your utility interconnection application in parallel with permitting rather than after construction, since interconnection timing affects tariff eligibility separately from code compliance.

A builder’s field checklist for staying ahead of plan review

We’ve seen permit reviews stall for weeks over details that take minutes to add during design. Before submitting, confirm whether your project triggers PV at all, calculate your SARA using a certified tool, and show the solar zone, conduit pathways, and inverter and meter locations directly on your plan set. Reserve busbar capacity and breaker space on the panel schedule, even if no system installs at construction.

Start your utility interconnection application early, and confirm tariff eligibility and any prevailing-wage obligations at that stage rather than waiting until the system is ready to energize.

Pro Tip: Bring your electrician into the conversation before the panel schedule is finalized. Reserved breaker space is cheap to plan for and expensive to retrofit.

Interconnection, billing, and prevailing-wage considerations

Once a system is installed, connecting it to the grid and understanding how it gets billed is a separate process from code compliance, governed by the California Public Utilities Commission’s customer-generation rules rather than the Energy Commission’s building standards.

Net Billing Tariff, often shortened to NBT, replaced the legacy net metering structure and changed how exported solar energy gets credited. Enrollment under NBT depends on when your interconnection application is submitted, so homeowners and builders benefit from applying as soon as system design is finalized rather than waiting until construction wraps up.

Prevailing-wage rules add another layer for certain projects. Under AB 2143, some larger customer-sited generation projects enrolling in specific tariffs must pay prevailing wages to qualify, a requirement worth confirming with your electrician or interconnection applicant before signing labor contracts. Because these rules intersect with tariff eligibility and project economics, we recommend starting the interconnection conversation at the same time you’re finalizing your electrical plan set, not after the system is physically installed. That sequencing avoids the scenario where a system is built and ready but enrollment delays push back when it can actually start generating credits.

How the mandate shapes custom home and remodeling projects

For anyone planning a custom home in Los Angeles, the solar mandate is no longer a line item to consider after the design is finished. It shapes roof orientation, panel schedule capacity, and even where mechanical equipment gets placed, since all of those decisions affect how much solar access roof area is actually available.

Remodeling projects face a narrower but still real impact. A complete remodel that expands conditioned floor area, or a significant addition, can trigger solar-ready obligations even if the original structure predates the mandate entirely. That makes early coordination between architect, electrician, and contractor more valuable than it used to be, since retrofitting conduit pathways or panel capacity after walls are closed up costs far more than planning for them upfront.

We approach every new custom build with these requirements considered from the earliest design conversations rather than treated as a late-stage compliance check. That’s a meaningful shift from how solar used to get handled on residential projects, where it was often an optional add-on discussed after the floor plan was locked. Now it’s part of the structural and electrical planning from day one, which tends to produce a cleaner permit submission and fewer change orders once construction starts.

Integrating solar PV and battery systems into remodeled homes

Working solar and battery infrastructure into an existing home looks different than designing it into new construction, mostly because you’re working around a roof, panel, and layout that already exist. The first question we ask on any remodel is whether the existing roof structure and orientation can support a meaningful solar zone, and whether the existing electrical panel has the capacity for future battery-ready wiring without a full service upgrade.

Roof material matters here too. Homes with standing seam metal roofing, common in several coastal communities we serve, often need specific mounting hardware designed for that roof type. For homeowners planning solar preparation on a metal roof, this guide to matching mount systems to metal roofing walks through the hardware considerations worth raising with your roofer before panels go on.

Integration tends to go smoothest when it’s planned alongside other remodeling work rather than as a standalone project. If a kitchen or whole-home remodel already involves opening up electrical panels or re-routing circuits, that’s the natural moment to add the conduit pathway and reserved breaker space a future system will need. Waiting until after the remodel is finished almost always means paying twice, once to close up walls and finishes, and again to open them back up for the electrical work.

Conduit routed through an open kitchen wall

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Permitting timelines for remodels and ADUs

Adding an ADU or undertaking a significant remodel introduces its own timeline pressures, and the solar mandate adds a layer most homeowners don’t anticipate when they first scope the project. If your ADU or addition increases conditioned floor area enough to trigger solar-ready requirements, that documentation needs to be part of your initial permit submission, not an afterthought addressed during plan check corrections.

We’ve found that projects move faster through plan review when solar-ready elements are shown clearly from the first submission rather than added in response to a reviewer’s correction letter. Each round of corrections can add weeks to a timeline that homeowners are often hoping to keep tight, especially for ADUs intended as rental income or housing for family members.

For ADU projects specifically, utility connections add another coordination point beyond the building permit itself. If you’re adding a new ADU, coordinating utility connections alongside your electrical panel planning helps avoid a scenario where the ADU’s utility service and the main home’s solar-ready infrastructure end up designed in isolation from each other.

Scheduling an ADU or remodel project with these requirements in mind from the start, rather than treating them as a late addition, tends to keep the permitting timeline closer to what homeowners originally expect.

What to discuss with your builder before design begins

The earlier you raise solar mandate compliance with your builder, the fewer surprises you’ll run into at plan review. A few specific questions are worth putting on the table during your first project planning conversation.

Ask whether your specific project, whether a new custom home, a major remodel, or an ADU, actually triggers the PV requirement, or whether it’s more likely to qualify for solar-ready-only treatment. Ask how your roof orientation and any shading from trees or neighboring structures might affect your solar access roof area, since that calculation shapes both your compliance path and your system sizing if you do install PV. If your project involves upgrading or replacing the electrical panel, ask specifically about reserved busbar capacity and breaker space for a future battery system, since that’s a detail easy to miss if it isn’t explicitly discussed.

For deeper background on how the 2025 and prior code cycles interact with remodeling specifically, our contractor-focused breakdown of the California Energy Code for remodels walks through more of the permit-level detail builders encounter on real projects.

A builder’s view on getting ahead of Title 24

The mandate rewards early planning more than it punishes any particular building type. We build Title 24 requirements into design conversations from day one, which keeps plan review moving and avoids costly rework later.

— David S.

How we help you build to the 2025 Energy Code

Navigating solar-ready, battery-ready, and PV sizing requirements is easier when it’s handled by a team that already builds to the 2025 Energy Code on every project. Whether you’re planning a new custom home, adding an ADU, or taking on a complete remodel, we integrate Title 24 compliance into the earliest design drawings rather than treating it as a late addition to the plan set.

Mrbuild

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Share your vision with us and schedule a personalized consultation to get started.
888-792-8453
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If you’re planning a new build, our custom homes team can walk through what the mandate means for your specific lot and roof orientation. If an ADU is part of your plans, our ADU and additions page is the right place to start a project planning conversation.

FAQ

Is solar going to be mandatory in California?

Solar PV is already required on most newly constructed single-family homes, qualifying multifamily buildings, and many nonresidential buildings under the 2025 Energy Code, with exceptions and solar-ready alternatives available for qualifying projects. Projects with permit applications on or after January 1, 2026 fall under this updated code cycle.

Are new homes in California required to have solar panels?

Most new single-family homes must include solar PV unless they qualify for one of five exceptions, such as limited roof area, a system size below the minimum threshold, or structural snow-load limits. Homes that qualify for an exception still must include solar-ready infrastructure like reserved roof zones and conduit pathways.

Is the 30% solar tax credit going away in 2026?

Federal solar tax incentives are set by federal legislation rather than California’s Energy Code, so this falls outside the scope of state building requirements covered here. We recommend confirming current federal incentive status with a tax professional or the Internal Revenue Service before finalizing a solar installation budget.

How is the required solar PV system size calculated?

Builders calculate PV size two ways, once using a conditioned-floor-area equation and once using solar access roof area multiplied by 18 watts per square foot for steep roofs or 14 watts per square foot for low-sloped roofs. The smaller of the two results is the system size that must be installed.

What happens if a battery storage system is installed instead of extra solar?

Installing a qualifying battery energy storage system with at least 7.5 kWh of usable capacity can reduce the required PV system size by 25% under the BESS exception. Installing that battery also satisfies the separate battery-ready infrastructure requirement, since the system itself fulfills that intent.

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