01Two approaches, not two levels of compliance
The prescriptive approach follows the applicable component and system requirements for the project. The performance approach uses CEC-approved compliance software to compare the proposed design against the standard design under edition-specific rules. Both must address mandatory requirements; performance is not permission to trade those requirements away.
Current planning starts with the 2025 California Energy Code for permit applications on or after January 1, 2026. The building type, project scope, climate zone and edition determine which requirements and modeling rules apply. A path that worked on a nearby project is a useful discussion point, not evidence that it will work here.
Evaluate a project-specific path with energy modeling and controlled option studies
02A practical path-selection checklist
Start with the design and evidence available, then test the appropriate path.
- +Is the scope and building classification established? Resolve those before comparing methods.
- +Does the selected design meet the applicable prescriptive provisions without unwanted changes? A prescriptive approach may avoid unnecessary option modeling.
- +Are glazing, envelope or equipment options central to design decisions? Ask whether performance modeling can evaluate allowable trade-offs.
- +Are existing-building features involved? Confirm the appropriate addition or alteration modeling rules and evidence requirements.
- +For either path, list mandatory measures and any installation, ECC verification or acceptance-testing obligations separately.
03Worked example: keeping a larger glazed opening
Hypothetical example: a designer wants to retain a larger glazed opening than a straightforward prescriptive design would accommodate. The team supplies the opening area, orientation, shading information and product performance to the modeler. Rather than promising that “better insulation will offset it,” the modeler evaluates permitted combinations using the applicable software and rules.
One option may reduce glazing; another may change window performance or other eligible measures. The team compares the compliant outputs and the real construction implications. A favorable result is tied to those modeled inputs. Substituting a different window later requires review; a previously passing model is not a blanket approval of any product.
04Read the result and the obligations
For a performance run, ask which design assumptions control the result, which measures must be shown on drawings and which require field verification. A preliminary option run is not the final permit package. Final output should match the coordinated plans and equipment schedules, with the applicable form signatures and registration addressed.
For a prescriptive package, ask which forms and supporting schedules establish compliance for the actual scope. “No energy model” does not mean “no documentation,” “no mandatory requirements,” or “no installer responsibilities.” The CEC publishes both registered and nonregistered single-family forms depending on the scope and verification needs.
05Keep code modeling separate from bill forecasting
Compliance software uses standardized assumptions and a code-defined comparison. It is not a forecast of utility bills or a guarantee of comfort, operating cost or permit approval. Mechanical sizing, detailed system design and construction quality remain their own work.
Use the CEC’s current manuals and approved-software information for the selected building and edition. Record the reason for choosing a path, the final assumptions and the verification handoff so the design decision remains understandable during plan check and construction.