2025 Building Energy Efficiency Standards for Residential and Nonresidential Buildings: Title 24, Part 6, and Associated Administrative Regulations in Part 1

Serving as a precursor to the first generation of building standards, the Department of Housing and Community Development adopted rudimentary energy conservation standards under their State Housing Law authority in 1975. However, the Warren-Alquist Act was passed one year earlier with explicit direction to the California Energy Commission (CEC, formally titled the State Energy Resources Conservation and Development Commission) to adopt and implement standards. 

The Building Energy Efficiency Standards (Energy Code) were first adopted in 1976 by the CEC and have been updated periodically since then, as directed by statute. The CEC’s statute created separate authority and specific direction regarding what the standards are to address, development criteria, and provided implementation tools, aids, and technical assistance. 

The Energy Code contains energy and water efficiency requirements (and indoor air quality requirements) for newly constructed buildings, additions to existing buildings, and alterations to existing buildings. Public Resources Code Sections 25402 subdivisions (a)-(b) and 25402.1 emphasize the importance of building design and construction flexibility by requiring the CEC to establish performance standards, in the form of an “energy budget” in terms of the energy consumption per square foot of floor space. For this reason, the Energy Code includes both a prescriptive option, allowing builders to comply by using methods known to be efficient, and a performance option, allowing builders complete freedom in their designs provided the building achieves the same overall efficiency as an equivalent building using the prescriptive option. Reference Appendices are adopted along with the Energy Code that contain data and other information that helps builders comply. 

The 2025 Energy Code development and adoption process continues a long-standing practice of combining technical rigor, challenging but achievable design and construction practices, public engagement, and full consideration of the views of stakeholders. 

The 2025 Energy Code builds on California’s technology innovations, encouraging energy efficient approaches to encourage building decarbonization, emphasizing in particular on heat pumps for space heating and water heating. This set of Energy Codes also extends the benefits of photovoltaic and battery storage systems and other demand flexible technology to work in combinations with heat pumps to enable California buildings to be responsive to climate change. This Energy code also strengthens ventilation standards to improve indoor air quality. This update provides crucial steps in the state’s progress toward 100 percent clean carbon neutrality by midcentury. 

Public Resources Code Section 25402.1 also requires the CEC to support the performance standards with compliance tools for builders and building designers. The Alternative Calculation Method (ACM) Approval Manual adopted by regulation as an appendix of the Energy Code establishes requirements for input, output, and calculational uniformity in the computer programs used to demonstrate compliance. From this, the CEC develops and makes publicly available free, public domain building modeling software in order to enable compliance based on modeling of building efficiency and performance. The ACM Approval Manual also includes provisions for private entities seeking to develop compliance software for approval by the CEC, which further encourages flexibility and innovation. 

The Energy Code is conceptually divided into three basic sets. First, there is a basic set of mandatory requirements that apply to all buildings. Second, there is a set of performance standards – the energy budgets – that vary by climate zone (of which there are 16 in California) and building type; thus the Energy Code are tailored to local conditions, and provide flexibility in how energy efficiency in buildings can be achieved. Finally, the third set constitutes an alternative to the performance standards, which is a set of prescriptive packages that provide a recipe or a checklist compliance approach.