Rescheck, Comcheck, and Manual J/S Reports
What Is the IECC?
The International Energy Conservation Code (IECC) is the model energy code most of the U.S. builds to. It sets the minimum efficiency requirements for new homes, additions, and commercial buildings: insulation, windows, doors, air sealing, duct leakage, HVAC, and lighting.
It’s a “model” code because there’s no national energy code. Building codes are state and local law. The International Code Council publishes the IECC, and then each state, or sometimes each city or county, decides which edition to adopt and whether to amend it. That’s why I’m always asking clients where their project is before anything else.
What the IECC Covers
The IECC has two separate sets of rules:
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Residential provisions cover one- and two-family homes, townhouses, and low-rise multifamily (three stories or fewer). Compliance is usually shown with a REScheck, plus Manual J and Manual S for HVAC sizing.
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Commercial provisions cover everything else, including mid- and high-rise multifamily. Compliance is usually shown with a COMcheck, and many jurisdictions also accept ASHRAE 90.1 as an alternative.​​​​
How the Editions Compare
Efficiency Improvements of IECC: Historic and Projected
2009 and 2012:
The big jump.
The 2021 IECC was a dramatic success story, resulting in over 10% energy gains over the 2018 version. Governmental members came out in record numbers to make it clear that they supported a more efficient model code.
2015 and 2018:
Barely moved.
The 2021 IECC was a dramatic success story, resulting in over 10% energy gains over the 2018 version. Governmental members came out in record numbers to make it clear that they supported a more efficient model code.
2021: Another real step up, with roughly 9% energy savings over 2018 according to DOE.
That includes higher ceiling R-values and tighter air leakage limits, and builders have to pick an additional efficiency measure.
2024: The latest edition.
It builds on 2021 and expands the menu of extra efficiency measures builders choose from.
Which Edition Applies to Your Project?
The one your jurisdiction has adopted, including any local amendments. Not the newest one, and not the one your last project used in another county. Climate zone matters too, because nearly every R-value and U-factor requirement changes by zone.
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Check your state on our Rescheck by State pages, or just ask me. I check the adopted edition and climate zone for every report before I run it.
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Need to Show IECC Compliance?
I prepare REScheck, COMcheck, and Manual J/S reports nationwide, built to the exact code edition your building department enforces.
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