Which Energy Code Compliance Path Fits Your Project Best?

The IECC and ASHRAE 90.1 — the two national model energy codes — both structure compliance around the prescriptive/performance split. The prescriptive path is deterministic: meet each section's minimums and you comply. The performance path is comparative: model the proposed building and a baseline, and prove the proposal wins. Some jurisdictions and above-code programs add outcome-based or measured-performance options that judge the occupied building's metered energy. The paths differ in engineering effort, review risk, and design freedom. Prescriptive compliance is the least effort and the most predictable at plan check, but it constrains design. Performance compliance costs more in modeling and documentation, faces more reviewer scrutiny, but frees the architecture and often produces a genuinely better building. Outcome-based compliance is the least effort at design and the most risk after occupancy.

The decision starts with the building. A single-story retail box with standard construction is a prescriptive building — the modeling would cost more than it could ever save. A mixed-use tower with extensive glazing, a data center, or any project chasing above-code certification is a performance building — the prescriptive path would either prohibit the design or force expensive component upgrades that modeling could avoid through trade-offs. Schedule and team matter too. Performance compliance needs an energy modeler engaged during design development, not during permit — late modeling only documents decisions that are already locked. And jurisdiction matters: some plan reviewers scrutinize performance submittals closely, which we account for in documentation quality, while others effectively require modeling for complex buildings. We make the path recommendation in writing during schematic design, with the cost and schedule implications stated plainly, because switching paths mid-project wastes the one resource no project has to spare: time.

The path decision belongs in schematic design, not at permit. Late switches mean rework. Work through these before the path is locked.

• Building complexity assessed: conventional and simple favors prescriptive, complex favors performance
• Trade-off value estimated: whether modeling flexibility is worth the modeling cost
• Modeler engaged early: performance path needs modeling during design, not after
• Jurisdiction expectations checked: reviewer scrutiny and local amendments for the chosen path
• Above-code goals aligned: certification or stretch-code targets may dictate the path