2024 International Energy Conservation Code (IECC): What You Need to Know

The 2024 International Energy Conservation Code, which aims to increase the energy efficiency of residential homes, was made available in July 2024. Whether you’re a builder, designer, architect or remodeler, you should understand this code and how you may need to incorporate its requirements into your next project.  

We’ll dive into the past, present and future state of the 2024 IECC.

The development of the IECC is managed by the International Code Council (ICC) as part of their suite of building codes. The intent of the IECC is to provide “enforceable [energy efficiency] requirements that achieve a reasonable level of energy efficiency” that is “lifecycle cost effective” for consumers and building owners.  

While the United States does not technically have a national energy code, the IECC is currently the basis for residential energy codes in 49 states (except California) and the District of Columbia. The residential portion of the IECC is written into federal legislation as a target efficiency for all states. States that do not comply with the requirements of the legislation may not be eligible for select DOE grant funds.

“The advent of energy codes in the United States can be traced back to the oil crisis of the 1970s, when a global energy shortage compelled the U.S. to address energy consumption in all sectors,” said Craig Drumheller, WDMA VP of Technical Activities and long-time participant in energy code development. 

Notable energy code milestones include: 

• 1975: American Society of Heating, Refrigerating and Air-Condition Engineers (ASHRAE) 90 Energy Efficiency Standard is created. 

• 1983: The Model Energy Code, the predecessor of the IECC, became the first widely adopted residential energy code in the U.S. 

• 1994: The Energy Policy and Conservation Act is amended to include a process where the U.S. Department of Energy compares the efficiency of the newly published MEC/IECC with that of the previous edition. 

• 1998: The first edition of the IECC is created. 

• Present Day: The IECC is updated on a triennial basis. 

Get an in-depth look at the history of the Residential Energy Code.  

The IECC is updated every 3 years. The development of the most recent iteration, the 2024 IECC, began in the fall of 2021 and underwent an extensive development process before being made available in July 2024.  

Noteworthy Changes

• Windows and Doors: A 7 to 10% increase in efficiency in northern climate zones. 

• Skylights: A 5 to 20% increase in efficiency across all climate zones. 

• Air Tightness: Homes must be approximately 20% tighter when tested using a pressurization test. 

• Attic Insulation: An 18 to 23% reduction in efficiency (addressed cost-effectiveness concerns). 

• Air Sealing, Insulation Installation Requirements: Updated requirements for sealing around windows, doors, fireplaces and common walls. 

• Efficiency Credits: Additional efficiency credits have been added beyond the typical prescriptive requirements. These new credits equate to approximately a 5% increase in efficiency. 

• Equipment Trade-Off: Limited trade-offs have been reinstated for heating, cooling and water heating equipment with efficiencies above the Federal minimum against other requirements for code compliance. 

Adoptable Appendices

Provisions in the appendices of the IECC are still adoptable by a jurisdiction but are not part of the base code. After successful appeals, the following provisions were moved to the appendices, as they concerned greenhouse gas reduction rather than building energy conservation.  

• Electric Vehicle (EV) Charging: Single-family homes with parking must have a 40 Amp 240 V receptacle nearby.  

• Solar Ready: All single-family homes must have roofs designed to be “solar ready,” including roof space allocation, a conduit from the attic to the electric panel, and sufficient panel space.  

• Electric Ready: Gas water heaters, dryers and stoves must have electric wiring back to the electric panel suitable for potential electric replacements.

Over the last four decades, the U.S. Department of Energy (DOE) has monitored the efficiency improvements in energy codes. While the DOE has not yet published their official determination of the improvements made by the 2024 IECC, past improvements can be seen in the figure below:

Though the 2024 IECC has been made available, it has not yet been adopted by any states. Here is what happens now: 

1. DOE Determination. The DOE will need to publish its determination on the 2024 IECC changes and confirm if the revised code improves energy efficiency in residential buildings.   DOE has 12 months from publication to complete its determination. Note: Preliminary analysis from DOE shows that the first draft version of the 2024 IECC was roughly 8% more efficient than the 2021 edition.

2. State Review. Though states are not required to adopt the new code, they must confirm with the DOE within 24 months of the final determination that they have reviewed the new building code and accommodated any public input. Then, they report whether they will revise their energy code based on the 2024 IECC. Failure to do so could result in the loss of certain DOE funding.

3. State Adoption. This process differs from state to state but typically includes an opportunity for stakeholders to provide input. States may choose legislative adoption, regulatory adoption, or delegation to local jurisdictions to adopt the new energy code. 

As of June 2024, here is a breakdown from the DOE on state code adoption status. Get more details on the entire state energy code adoption process

“Building energy codes that are both reasonable and cost-effective are critical in advancing energy efficiency in residential buildings. Their implementation and enforcement are key to reducing energy consumption and promoting sustainability.”

— Craig Drumheller