2025 Low-rise Multifamily Solar PV

Section 170.2(f) - PDF of the 2025 Energy Code requires solar photovoltaic (PV) systems for all newly constructed low-rise multifamily buildings (buildings up to three habitable stories), with five exceptions, see below. 

These requirements do not apply to additions or alterations to existing buildings. 

The required solar PV size is calculated per Section 170.2(f) - 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 170.2(f) - 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 access roof access area (SARA) or based on Equation 170.2-C:  

• Solar access roof area (SARA):
  • Steep-sloped roofs: SARA multiplied by 18 watts per square foot
  • Low-sloped roofs: SARA multiplied by 14 watts per square foot
• Equation 170.2-C – PDF considers three factors:
  • Climate zone (CZ) of the building
  • Conditioned floor area 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 (BESS) that is compliant with the 2025 Energy Code Reference Joint Appendix JA12 can reduce the required solar PV system size. 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. Installing a larger solar PV system cannot be exchanged for less energy efficiency measures. A battery energy storage system is not required for low-rise multifamily buildings, but it may be modeled for compliance credit under the performance approach.  

Yes. There are five exceptions that exclude low-rise multifamily 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 required if minimum solar PV system size is less than 4 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 storage system (BESS), the solar PV size per Equation 170.2-C may be reduced by 25 percent. The battery 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, 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)-(d) - PDF are mandatory, but only apply to: 

• Newly constructed low-rise multifamily buildings without a solar PV system
• Additions where the total roof area is increased by more than 2,000 square feet 

For information on high-rise multifamily buildings, please visit the 2025 High-rise Multifamily Solar PV Factsheet.

No. The prescriptive requirements for solar PV and battery energy storage systems (BESS) only apply to newly constructed buildings. 

Yes. Since the dining area is part of the living facility, the entire building is considered multifamily. The dining area would only be considered a restaurant if it is designed to serve outside customers. Depending on the number of habitable stories, the solar PV requirements in the 2025 Energy Code Sections 170.2(f-g) will apply to the entire building.

Yes. Exception 2 to Section 170.2(f) - PDF applies to each building (not individual dwelling units). If the minimum solar PV size specified is less than 4 kW, then no solar PV is required for that building.

See the Blueprint for more information, including articles and frequently asked solar PV questions about the 2025 Energy Code.