Two energy codes dominate commercial construction in the United States: ASHRAE Standard 90.1 and the International Energy Conservation Code (IECC). They cover similar ground — building envelope, lighting, HVAC, and service water heating — but they are different documents, maintained by different organizations, and adopted differently by states and municipalities. Knowing which one governs your project determines your compliance obligations before design begins.
What Is ASHRAE 90.1?
ASHRAE Standard 90.1, Energy Standard for Sites and Buildings Except Low-Rise Residential Buildings, is published by the American Society of Heating, Refrigerating and Air-Conditioning Engineers. It is a consensus standard, not a building code — but it is adopted by reference in the IECC and directly by many states as the commercial energy compliance path. ASHRAE 90.1 is updated on a roughly three-year cycle; current widely-adopted editions include 2019 and 2022.
What Is the IECC?
The International Energy Conservation Code is published by the International Code Council (ICC) — the same body that produces the IBC and IPC. The IECC has two distinct parts: a residential section and a commercial section. For commercial buildings, the IECC's commercial provisions are technically equivalent to ASHRAE 90.1 in most editions — the IECC often simply adopts 90.1 by reference for commercial projects, or runs a parallel prescriptive path that achieves the same energy targets.
How Are They Related?
The short answer: they are closely aligned but not identical. The IECC commercial provisions and ASHRAE 90.1 have been explicitly coordinated since the 2015 cycle so that compliance with one generally satisfies the other. However, differences exist in specific table values, mandatory measures, and how climate zones are defined. When a state adopts the IECC with local amendments, those amendments may further diverge from ASHRAE 90.1.
Which Code Applies to My Project?
The answer depends on your jurisdiction:
- State adoption — each state adopts a base energy code (either ASHRAE 90.1, the IECC commercial provisions, or a state-specific code like California's Title 24) and may amend it.
- Federal projects — federally owned or leased buildings must comply with 10 CFR Part 433, which references ASHRAE 90.1 at the edition specified by the Department of Energy.
- HUD and USDA programs — projects receiving federal housing funding often have energy code requirements tied to specific IECC or ASHRAE editions.
- Utility incentive programs — programs offering rebates for above-code performance typically reference ASHRAE 90.1 as the baseline.
ASHRAE 90.1 Climate Zones vs. IECC Climate Zones
Both standards use the same eight-zone climate classification system (Zones 1–8, with moisture designations A/B/C). The county-level zone assignments are largely consistent between them, though differences exist in a handful of locations. Your MEP engineer or energy modeler will confirm the correct zone assignment for your building address before beginning compliance analysis.
Prescriptive vs. Performance in Each Code
Both ASHRAE 90.1 and the IECC offer prescriptive and performance compliance paths:
- Prescriptive — each system must individually meet minimum requirements; no trade-offs between systems
- Performance (Energy Cost Budget in 90.1; Total Building Performance in IECC) — energy modeling demonstrates that the proposed building's energy cost or use equals or beats a code-compliant baseline
- ASHRAE 90.1 Appendix G — the LEED energy credit baseline; used for above-code certifications, not for permit compliance
What Your Engineer Needs to Know
When you engage an MEP engineer for a commercial project, they need to confirm: (1) the adopted code and edition in your jurisdiction, (2) any local amendments that modify the base code, (3) whether the project qualifies for any exceptions, and (4) the compliance path best suited to the project design.
Bottom Line
For most commercial projects outside California, you're working with either ASHRAE 90.1 or the IECC commercial provisions — and in many states they're functionally equivalent. What matters is knowing which edition your jurisdiction has adopted and what local amendments are in effect. Your MEP engineer should make this determination at project kickoff, not at permit submission.