California Building Standards Code “Title 24” includes regulations for building energy efficiency in California. In 2023, the updated Title 24 code went into effect. Previously, it only required that building plans be designed to accommodate the installation of solar in the future. The new code requires that a certain amount of solar actually be installed, along with some amount of battery capacity, in certain cases.
Many construction projects have been caught off guard by the requirement to install PV systems and battery systems on new buildings. If these weren’t part of the original budget or if space was not allocated for the additional equipment, then there can be major problems. Projects have experienced incredible budget over-runs and delays, as a result.
If you’re an architect, developer, builder or commercial property owner, it is helpful to understand the code requirements – not only to anticipate them in advance, but also to see what solutions may be possible, if you’re already in a bind.
Unfortunately, the code that went into effect is not simple, and it can be difficult to spot those solutions. At Xero Solar, we understand the nuances of the code, and even the approved exceptions.
To help you navigate the standards and what they mean for your building, we’ve developed a synopsis. For more information, the relevant Title 24 code can be found in Section 140.10 and 170.2. If you need help with meeting the solar and battery requirements, you can reach out to Xero Solar for guidance.
Meeting the Title 24 Solar Requirements for New Construction
There are three methods for calculating how much solar is required for your new build. You’re allowed to select whichever works for the project, even if the others would have required more.
“Prescriptive Methods”
There are two “prescriptive methods” that offer a formulaic, rules-based approach to compliance: the Condition Floor Area method and the Solar Access Roof Area “SARA” method. These simplify compliance, but can be restrictive for unique building designs.
The Conditioned Floor Area method follows a simple formula based on: building occupancy type (e.g., office, school, retail, etc.), location, and the total conditioned floor area of the building. For example, a new 100,000 square foot office building in Santa Monica will need 313,000 watts (313 kW) of solar capacity. It’s important to note that this formula is slightly different for low-rise multifamily buildings (e.g. apartment buildings with apartments on no more than 3 floors). The Conditioned Floor Area method tends to require the largest amount of solar.
The Solar Access Roof Area or “SARA” method is an even simpler formula based on 14 watts of solar for every square foot of roof space available for solar. For example, a cluttered roof that only has 5,000 sqft of space remaining for solar will only need 70,000 wats (70 kW). This method tends to require the least amount of solar.
SARA is great for roofs that already have lots of code-required equipment and clearances and setbacks. The trick is being able to justify to your plan-check engineer that much of the roof space is already not able to fit solar panels: HVAC units, fire-access pathways, OSHA-required maintenance-access pathways, etc. Some plan-checkers may even accept roof decks as acceptable carve-outs from the SARA square footage. If the SARA square footage ends up being less than 3% of the conditioned floor area square footage, there is a specific Exception listed in the code, stating that no solar is required. Similarly, if the SARA contains less than “80 contiguous square feet,” no solar is required.
The “Performance Method”
Unlike the Prescriptive Methods that use simple formulas, the Performance Method uses a specific software program to assess the building design holistically. It requires a myriad of energy efficiency variables to be input into EnergyPro software, by EnergySoft.
This is often used if an element of the building design can’t satisfy its own Prescriptive requirements. For example, maybe the designs call for a large, all-glass atrium, that cannot satisfy Prescriptive requirements for the building envelope. That project could still satisfy Title 24 by using the Performance method and overcompensating for the glass atrium with additional solar.
Conversely, this method is handy if there is limited budget to include solar. You can reduce the amount of solar necessary, if other elements of the building design are especially energy-efficient: higher SEER ratings for HVAC, thicker insulation, etc.
While it’s important to understand these 3 methods, it’s just as helpful to know the listed Exceptions, which may exclude a project from needing to install solar at all. For example, one Exception says if a calculation shows less than 4 kW is required, then no solar is needed.
Understanding the Battery Storage System Requirements
Title 24 requires a battery system for all commercial building types except one: low-rise multifamily buildings. For those buildings, if a battery system is voluntarily installed, the required amount of solar is reduced by 25%. For all other building types – including high-rise multifamily – batteries are required, and they do not change the amount of solar required. For those buildings, there are two methods for calculating the battery system size.
First, it’s important to know that battery capacity is defined by two values: kW power capacity, and kWh energy storage capacity. This is distinct from solar capacity, which is only defined by one value: kW power capacity.
The “Prescriptive Method”
The “Prescriptive Method” is a simple formula for each of those two values, based on building occupancy type and required solar kW power capacity. The formula for kWh energy storage capacity does also include the square-root of the battery inverter’s rated efficiency. But that variable doesn’t change the result much: the square-root of 80%-100% efficiency is very close to 1. This Prescriptive method is convenient enough if the solar capacity is also determined by one of the Prescriptive methods.
The “Performance Method”
If the solar capacity is determined using the Performance method, on the other hand, then the battery capacity will be too. The Performance Method calculation for batteries is part of the same holistic assessment of the building’s designed energy efficiency. In most cases, when one energy-efficiency variable decreases, others must increase. However, that inverse relationship is not the case for solar and battery capacity. The computer software maintains a directly proportional relationship between solar and battery capacity: if solar must increase, so too must the battery. And, strangely, if solar decreases, so does the battery.
Again, Exceptions are crucial for finding feasible battery solutions. No batteries are needed if the required energy storage capacity is less than 10 kWh. Title 24 is merciful in that it doesn’t require a battery, if the calculated requirement is so small that there would hardly be any value in putting it even on a single-family home.
Another Exception for the battery requirement has to do with the solar capacity: no battery is required if the required solar capacity is less than 15% of what would have been required based on the Conditioned Floor Area calculation. This is for cases when solar capacity is determined by on the SARA method or Performance method. For example, if a project is calculating the solar capacity using SARA, and that required capacity is only 10% as much as what would have been required by the Conditioned Floor Area calculation, no battery system is required.
As you see, Title 24 is not simple. There are many paths to compliance, each with its own limitations and benefits. The more familiar you are with each of the methods and all of the exceptions, the better chance you have of coming up with a solution that works for the project budget and the building design parameters. If you need help problem solving, reach out to Xero Solar, and we can help you navigate through the complexity.
