Title 24 requires certain minimum features to be installed in all new construction projects, called the Mandatory Measures. This then allows the builder to choose either a prescriptive or performance path to complete the energy budget portion of the efficiency requirements in construction.
Section 1.6 of the Nonresidential Compliance Manual offers further explanation of the Mandatory Measures and Compliance Approaches.
The prescriptive approach is more direct but offers relatively little design flexibility; some building envelope components, such as walls, where portions of the wall that do not meet the prescriptive insulation requirement may still comply as long as they are area-weighted with the rest of the walls, and the average wall performance complies. If the design fails to meet even one of the requirements, the system does not comply with the prescriptive approach and the performance approach must be taken.
Tip: a common disqualifier for the nonresidential prescriptive approach is that window to wall ratio cannot exceed 40%.
For detailed language about prescriptive requirements for each building component in the Nonresidential Compliance Manual, click on the below links:
The performance approach allows trade-offs between different building components (wall, roof, windows, infiltration, equipment, etc.), as long as the overall proposed building energy consumption is shown to be better than the baseline building defined by the standards. These trade-offs are determined either through hourly computer simulations or derived from simulation results. The performance approach may be used for envelope or mechanical compliance; envelope and mechanical compliance; envelope and indoor lighting compliance; or envelope, mechanical and indoor lighting compliance. It is not applicable to outdoor lighting, or to indoor lighting in the absence of envelope compliance.