International Energy Conservation Code

Buildings consume about 40% of the energy our nation uses, so making buildings as efficient as possible is important. The International Energy Conservation Code sets out minimum efficiency standards for new construction for a structure’s walls, floors, ceilings, lighting, windows, doors, duct leakage and air leakage.

The IECC is referred to as a model energy code* because building codes are state or local laws; there is no national building energy code in the US. Regardless of when any state adopts a code, every three years, the IECC is updated to incorporate new building technologies and practices as they evolve over time, and ensure that new American homes and commercial buildings meet modern-day minimum levels of efficiency. In previous cycles, officials from municipalities and states across the nation voted on the proposed changes; starting with the 2024 IECC, the code is determined by committee members, representing nine different categories, including governmental regulators.

The IECC serves as the go-to source for states adopting an energy code; an ICC code is in use or adopted in all 50 states and beyond. That’s why it’s important to get each three-year version right, so that states can be confident they’re adopting an updated, well-vetted, and feasibly implementable building energy code.

*The IECC is the model residential energy code in the US; for commercial buildings, ASHRAE 90.1 is considered the model code, though the majority of states adopt the commercial IECC with the option to comply via ASHRAE 90.1.

History of the International Energy Conservation Code

For nearly two decades, successive versions of the IECC and its predecessor, the Model Energy Code (MEC), made only 1 to 2 percent gains in energy efficiency. That changed in 2009 and 2012, when the Energy-Efficient Codes Coalition (EECC) brought together government and business leaders, regional energy efficiency alliances, academics, think tanks, utilities, conservation groups, low-income housing groups and energy consumers to support a 30+ percent energy efficiency boost, as can be seen in the adjacent graph.

After the progressive gains made to the 2009 and 2012 IECCs, progress stalled as anti-efficiency lobbyists successfully halted further progress during the 2015 and 2018 code cycles. These lost opportunities for efficiency gains in the 2015 and 2018 IECCs set us behind and have cost homeowners and business owners thousands in lost revenue due to buildings being constructed to weaker standards than is feasible today.

The 2021 code cycle once again resulted in significant progress, with an efficiency boost of more than 10% over the 2018 IECC.

Energy Code Timeline

the 2009/2012 proposal

The 2012 proposal – called “The 30 Percent Solution” – was the first comprehensive efficiency proposal ever offered before the International Code Council. After 14 of its 21 provisions were incorporated into the 2009 IECC, we improved and offered the remaining provisions during the 2012 IECC development cycle.

2015 and 2018 IECCs

During development of the 2015 and 2018 IECCs, local and state public officials from across the U.S. rejected an anti-efficiency campaign by efficiency opponents who attempted to roll back the historic, 30% efficiency gains from the 2009 and 2012 IECCs. The results were 2015 and 2018 IECCs that are only slightly more energy efficient than the 2012 version.

2021 IECC

The 2021 IECC was a dramatic success story, resulting in over 9% 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.

2024 IECC

For the 2024 IECC, the ICC changed the development process from a codes process, where governmental members make the final determination on the content of the code, to a standards process, where committees make the final decision on the outcome of the IECC. The fate of the 2024 IECC remains to be seen.

Additional Resources

Fact Sheets

HUD Determination Fact Sheet (ACEEE)

This fact sheet produced by ACEEE details why HUD’s proposal to update the referenced energy codes to the 2021 IECC/ASHRAE 90.1-2019 is so important.

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