Title 24 Solar Requirements for New Commercial Buildings in California

California's Title 24 building energy code now requires many new commercial buildings to actually install solar, and in most cases battery storage, rather than simply designing for it in the future. The 2023 update changed the rule significantly, and project teams that don't plan for it early can face serious budget and schedule problems. Here is what architects, developers, builders, and commercial property owners need to know about the requirements, the calculation methods, and the exceptions that may apply.

What Changed in the 2023 Title 24 Update

Previously, Title 24 only required that building plans be designed to accommodate a future solar installation. The updated code goes further: it requires that a defined amount of solar capacity actually be installed, along with battery capacity in most cases. Many construction projects have been caught off guard by this shift. If solar and battery systems weren't part of the original budget, or if roof space wasn't reserved for the added equipment, the result can be significant cost overruns and delays late in the project.

The relevant code sections are 140.10 and 170.2 of the California Energy Code. The rules are not simple, but there are real opportunities within them, including approved exceptions that can reduce or eliminate a project's obligation. Understanding the methods and exceptions early gives a project team far more flexibility than discovering them after design is locked.

Three Ways to Calculate Required Solar Capacity

A project can choose whichever of the three calculation methods works best, even if the others would have required more solar capacity.

Conditioned Floor Area Method

This prescriptive method uses a formula based on building occupancy type (office, school, retail, and so on), location, and total conditioned floor area. As an example, a new 100,000 square foot office building in Santa Monica would need roughly 313 kW of solar capacity under this method. The formula differs slightly for low-rise multifamily buildings. Of the three methods, this one tends to require the largest amount of solar.

Solar Access Roof Area (SARA) Method

SARA is a simpler formula: 14 watts of solar capacity for every square foot of roof space actually available for solar. A roof with only 5,000 square feet of usable space, for instance, would need about 70 kW. This method tends to require the least amount of solar, and it works well for roofs already crowded with HVAC units, fire access pathways, maintenance clearances, and similar equipment, provided that clutter can be justified to the plan-check engineer as legitimate carve-out space. If the SARA area comes out to less than 3 percent of the conditioned floor area, or less than 80 contiguous square feet, an exception in the code eliminates the solar requirement entirely.

Performance Method

Rather than a simple formula, the Performance Method evaluates the building holistically using EnergyPro software from EnergySoft, with a range of energy efficiency variables as inputs. This method is useful when a design element, such as a large glass atrium, cannot meet prescriptive requirements on its own; additional solar can offset that shortfall. It can also work in the opposite direction, reducing the required solar amount if other parts of the building are especially efficient, such as higher SEER-rated HVAC systems or thicker insulation.

A project can choose whichever calculation method works best for its design, and the listed exceptions, including one that eliminates the requirement entirely below 4 kW, are often the key to a workable solution.

Battery Storage Requirements

Title 24 requires a battery system for nearly every commercial building type, with low-rise multifamily as the notable exception. For low-rise multifamily buildings, installing a battery voluntarily reduces the required solar capacity by 25 percent. For every other building type, including high-rise multifamily, a battery is required and does not reduce the solar requirement.

Battery capacity is defined by two values, kW power capacity and kWh energy storage capacity, and is calculated using either the Prescriptive or Performance method, matching whichever method was used to determine solar capacity. Under the Performance Method, solar and battery capacity move together: if the software increases the required solar, it increases the required battery as well, and vice versa.

• No battery is required if the calculated energy storage capacity is less than 10 kWh.
• No battery is required if the required solar capacity is less than 15 percent of what the Conditioned Floor Area method would have required, when solar was determined using SARA or the Performance Method.
• Low-rise multifamily buildings can opt into a battery voluntarily to reduce their solar requirement by 25 percent.

Planning Ahead Protects Your Budget

Because there are multiple compliance paths and a range of exceptions, the amount of solar and battery capacity a given building actually needs can vary considerably based on how the project is approached. Architects, developers, and property owners are best served by working through these calculations during early design, not after construction documents are finalized. If you are planning a new commercial building and want help identifying which method fits your project, or you are trying to solve a solar requirement that wasn't accounted for in the original budget, reach out to Xero Solar for guidance. It's also worth understanding how current federal tax incentives for commercial solar interact with these requirements, since a required system may also qualify for meaningful credits.

Frequently asked questions

Does every new commercial building in California need solar panels?

Most new commercial buildings do, under the current Title 24 code, but there are listed exceptions. For example, if the calculated solar requirement comes out under 4 kW, no solar is required at all. Small footprints, cluttered roofs, and certain building types can also reduce or eliminate the requirement.

What are the three methods for calculating required solar capacity?

The Conditioned Floor Area method, the Solar Access Roof Area (SARA) method, and the Performance Method. A project can choose whichever method works best for its design, even if the others would have required more solar.

Is battery storage required for new commercial buildings?

Yes, for most commercial building types, with low-rise multifamily buildings being the main exception. For low-rise multifamily, a voluntary battery reduces the required solar amount by 25 percent instead. There are also exceptions that eliminate the battery requirement when the calculated capacity is very small.

What happens if solar wasn't included in the original building budget?

This is a common and costly problem. Projects that did not anticipate the Title 24 solar and battery requirements have experienced significant budget overruns and delays. The earlier a project team understands which compliance method and exceptions apply, the more options remain for controlling cost.

Where can I find the official Title 24 solar and battery code language?

The relevant sections are 140.10 and 170.2 of the California Energy Code, published by the California Department of General Services Building Standards Commission. Because the code includes multiple calculation methods and exceptions, most project teams benefit from working through it with an experienced solar partner.