Prescriptive vs. performance: the two ways to comply with Title 24

Every residential project in California shows Energy Code compliance one of two ways. Both are legitimate; they suit different projects.

Prescriptive: meet every requirement

The prescriptive path lists requirements for your climate zone, such as insulation levels, window performance and equipment efficiency. If the design meets each one, it complies. No software is needed, but there's no flexibility: miss one item and the design doesn't comply, even if it's better elsewhere.

Performance: model the building

The performance path models the proposed building in CEC-approved software and compares it against a standard design built to the prescriptive requirements. If the proposed design does as well or better, it complies. That allows trade-offs, like offsetting large windows with a better heat pump.

Which one to use

• Simple alterations and small additions that already meet every requirement: prescriptive is usually quicker.
• New homes and ADUs, or any design with lots of glass or unusual assemblies: performance usually gives more room and a clearer picture.

The CEC's own residential software, CBECC, runs the performance calculation. Other approved programs use it underneath too.