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International Energy Conservation Code (IECC)

Buildings consume about 40% of the energy our nation uses, so making buildings as efficient as possible is important. America’s model energy code — called the International Energy Conservation Code or IECC — 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 America’s model energy code because building codes are state laws; there is no national building energy code. Regardless of when any state adopts a code, every three years, officials from municipalities and states across the nation vote on proposed changes to the IECC 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 safety, fire protection, and efficiency.

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.

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 2012 IECC

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. 

The 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.

The 2021 IECC

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.

Efficiency Improvements of IECC:
Historic and Projected

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