Frequently asked questions about the single-family solar photovoltaic (PV) requirements for the 2025 Energy Code.
General Information
Section 150.1(c)14 - PDF of the 2025 Energy Code requires solar photovoltaic (solar PV) systems or modules for all newly constructed single-family residential buildings, with five exceptions (see accordion describing exceptions below). These are defined as:
- Townhouses
- Residential building of occupancy group R-3 with two or less dwelling units
- Buildings of occupancy groups:
- R-3, other than a multifamily building or hotel/motel building
- R-3.1
- U, when located on a residential site
These requirements do not apply to additions or alterations to existing buildings, or unconditioned buildings.
The required solar PV size is calculated per Section 150.1(c)14 - PDF. A building’s energy demand is impacted by its climate zone (CZ), conditioned floor area (CFA) and number of dwelling units. The minimum required solar PV system is intended to offset approximately the electrical consumption of the proposed building, as if it were a mixed fuel building (assumes a natural gas furnace, water heater, stove, and clothes dryer). This means electric heat pump space heating and water heating loads, and electric appliances will not affect the minimum solar PV system size requirement. The climate zone, conditioned floor area, and possible plug loads of a building will affect its cooling demand and therefore its required solar PV system size.
Prescriptive Requirements
Section 150.1(c)14 - PDF of the 2025 Energy Code outlines two methods to determine the minimum solar PV system size. The required size is the smaller of either the capacity based on solar roof area (SARA) or based on Equation 150.1-C -PDF:
- Solar access roof area (SARA):
- Steep-sloped roofs: SARA multiplied by 18 watts per square foot
- Low-sloped roofs: SARA multiped by 14 watts per square foot
- Equation 150.1-C considers three factors:
- Climate zone (CZ) of the building
- Conditioned floor area (CFA) of the dwelling(s)
- Number of dwelling units
Solar access roof area (SARA) includes roof areas, covered parking, carports, and newly constructed structures on the property that can support a solar PV system per Title 24, Part 2, Section 1511.10. SARA excludes roof areas:
- With less than 70 percent annual solar access accounting for shading from obstructions
- For steep sloped roofs, only existing permanent obstructions external to the building (e.g., trees, hills, nearby structures)
- For low sloped roofs, all obstructions including external obstructions and those that are part of the building design and elevation
- Occupied as specified by California Building Code Section 503.1.4
- Roof area otherwise unavailable due to compliance with:
- Other state building code requirements
- Local building code requirements if confirmed by the California Energy Commission Executive Director
Performance Compliance
The minimum solar PV system size requirement will be based largely on the factors described above. Adding a battery energy storage system can reduce the required solar PV system size and can provide a self-utilization credit against the energy efficiency requirement if the battery energy storage system complies with the 2025 Energy Code Reference Joint Appendix JA12-PDF. Additionally, increasing the building’s energy efficiency (e.g., installing more efficient space cooling, increased insulation, etc.) will decrease its electrical consumption and decrease the required solar PV system size.
Note: Installing a larger solar PV system cannot be exchanged for less energy efficiency measures without installation of a JA12-compliant battery energy storage system.
Yes. There are five exceptions that exclude single family buildings from the solar PV requirements, or reduce the required system size:
- No PV system required if
- SARA less than 80 contiguous square feet
- For steep-sloped roofs, SARA excludes roof areas facing between 300 and 90 degrees from true north
- No PV system is required if minimum solar PV system size specified by section 150.1(c)14 is less than 1.8 kWdc.
- No PV system required if the enforcement authority determines the solar PV system cannot meet the American Society of Civil Engineers Standard 7-16, Chapter 7, Snow Loads requirements
- Buildings approved by the local planning department prior to January 1, 2020, with mandatory conditions of approval
- If installed in conjunction with a battery energy storage system (BESS), the solar PV size per Equation 150.1-C may be reduced by 25 percent. The battery energy storage system must meet Reference Joint Appendix JA12 requirements, and have a minimum cycling capacity of 7.5 kWh
No. Solar PV systems can be installed on the building’s SARA such as, ground-mounted on the property, or mounted atop a carport installed on the lot. Note: an alternative to installing solar PV on-site is to comply with community solar requirements when using the performance compliance approach if the CEC has approved a community solar program for the building type in the area where the building is located.
The solar-ready requirements under Section 110.10(b)-(e) - PDF are mandatory but only apply to newly constructed single-family buildings that do not require a solar PV system located in subdivisions with ten or more single-family residences, where the tentative subdivision map is deemed complete or approved by the enforcement agency. Note that solar-ready requirements do not apply to newly constructed accessory dwelling units built on an existing lot.
Frequently Asked Questions
No. For example, Exception 2 to Section 150.1(c)14 - PDF applies when either Equation 150.1-C outputs less than 1.8 kWdc or the solar roof access area (SARA) does not allow a 1.8 kWdc system to fit on the roof. Exception 5 to Section 150.1(c)14 reduces required PV size by 25 percent when installing a battery energy storage system (BESS). Exception 2 cannot be combined with the application of Exception 5. When Exception 5 applies then the project requires both PV and battery energy storage system to be installed.
Yes. The performance modeling software allows Exception 2 to Section 150.1(c)14 - PDF, when the minimum solar PV system size is less than 1.8 kWdc determined by Equation 150.1-C. Per the 2025 Single-Family Residential Alternative Calculation Method (ACM) Reference manual, the standard design is based on Equation 150.1-C. Therefore, if the user wants to claim Exception 2 to Section 150.1(c)14, the calculated PV system size per Equation 150.1-C must be less than 1.8 kWdc.
Yes. A conditioned, newly constructed building classified as occupancy group U on a residential lot needs to meet the solar PV requirements in Section 150.1(c)14 - PDF of the 2025 Energy Code. Using the prescriptive method, the annual solar PV electrical output Equation 150.1-C allows for an input of zero for the number of dwelling units, therefore the required kWdc is zero. Using the performance method, the solar PV calculation is automated to at least one dwelling unit.
Yes. The 2025 Energy Code does not specify where new solar PV modules must be installed. Adding new solar PV modules to an existing solar PV system will satisfy the solar PV requirements in Section 150.1(c)14 - PDF if the added solar PV modules are on the same residential lot as the ADU and expansion of the solar PV system is allowed by the load-serving entity. The 2025 Energy Code does not regulate whether the added solar PV modules are serving the ADU meter or the main house meter. Any added solar PV modules must also comply with other parts of the building code as applicable.
No. The ADU must have a newly installed solar PV system to meet the requirements.
Yes. New solar PV modules may be added to an existing solar PV system to meet the 2025 Energy Code requirements. The new solar PV modules must be part of the ADU’s permit application, sized per the Energy Code, and comply with other parts of the building code as applicable.
No. Per Section 110.10(a)1 - PDF solar ready applies to new single-family homes located in subdivisions of ten or more. Therefore, solar ready is not applicable to a newly constructed ADU on an existing lot.
Yes. Section 150.1(b)1 – PDF allows the use of an approved community shared solar generation system instead of installing solar PV panels on the building.
See the Blueprint for more information, including articles and frequently asked solar PV questions about the 2025 Energy Code.