2025 Nonresidential and Multifamily Alternative Calculation Method Reference Manual: for the 2025 Building Energy Efficiency Standards

The California Energy Commission’s (CEC) 2025 Building Energy Efficiency Standards for residential and nonresidential buildings allow compliance by either a prescriptive or performance method. The performance compliance approach uses computer modeling compliance software to trade-off efficiency measures. Performance compliance is the most popular compliance method because of the flexibility it provides in building design.

Compliance software must be certified by the CEC, following rules established for modeling compliance software. This document establishes the rules for creating a building model, describing how the proposed design is defined, explaining how the standard design is established, and reporting on the performance compliance certificate. This document also describes the procedure for performance calculation, necessary rule sets, reference method for testing compliance software accuracy, and the minimum reporting requirements. The CEC reserves the right to approve vendor software for limited implementations of what is documented in this manual.

This Nonresidential and Multifamily Alternative Calculation Method Reference Manual explains how the proposed and standard designs are determined. The explanations for single-family building proposed and standard designs are described in the Single-Family Residential Alternative Calculation Method Reference Manual.

The compliance manager, public domain compliance software provided by the CEC, is called California Building Energy Code Compliance (CBECC). CBECC and all third-party compliance software must meet rules described in the Nonresidential and Multifamily Buildings ACM Reference Manual.