How Do Solar Panels and Batteries Count in a Title 24 Calculation?
Solar answers the total energy budget, not the efficiency budget. More panels cannot rescue a design that fails on efficiency, because solar has no effect on the efficiency metric. A battery can shrink the required array and, paired with solar, release a small credit for efficiency trade-offs.
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The size rule in brief
The required system is the smaller of two figures: (floor area times a floor-area factor) divided by 1,000 plus a per-dwelling-unit factor, both from Table 150.1-C, or the usable roof area times 18 for steep roofs or 14 for low-slope roofs. Nothing is required when the computed size is under 1.8 kWdc or the roof area with at least 70 percent annual solar access, on steep roofs excluding northerly azimuths, is under 80 contiguous square feet.
Why panels cannot fix an efficiency shortfall
The performance method keeps two scores. Efficiency long-term system cost covers space conditioning, water heating and ventilation; total cost adds solar, batteries and lighting. Solar has no effect on the first score, so a gas furnace or weak envelope cannot be offset by a bigger array. The manual points the other way: a more efficient design may comply with a smaller solar system. See the heat pump page for the offset side.
How the performance model sizes solar
The reference array is set from the modeled annual electricity use of the mixed-fuel proposed design, regardless of the fuel you actually choose. You may model other sizes, and that is where a larger array earns credit on the total score.
What a battery does
- Prescriptively, a battery with at least 7.5 kWh of cycling capacity allows the array to be 25 percent smaller.
- In the performance path, solar paired with a battery of at least 5 kWh of compliance cycling capacity releases a modest credit for efficiency trade-offs.
- A stand-alone battery releases none.
Special cases
A community shared solar or storage system approved under Section 10-115 may offset part or all of the requirement. A new detached ADU may add modules to the main house system, but existing panels do not count; see that question and battery storage rules. Hand-sizing is in the calculator page, and the solar requirements page lists exemptions. Order a residential report to see the numbers for your plan.
Common Title 24 Questions
- When is Title 24 required for a home?
- Does a remodel need Title 24?
- Does a room addition need Title 24?
- What plans are needed for a residential Title 24 report?
- How much does a residential Title 24 report cost?
- How long does a residential Title 24 report take?
Frequently Asked Questions
It satisfies the solar requirement and the total energy score, but it cannot fix a shortfall in the efficiency score.
No. The photovoltaic requirement does not apply to additions or alterations, though a new detached ADU needs its own.
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