The International Code Council (ICC) recently released its latest model International Energy Conservation Code** IECC 2024**. The IECC was created in 2000 and has been adopted by many code offices across the USA. The code is updated every 3 years and is the industry standard for energy codes in the USA. Understanding the updates to IECC 2024 is very important to HERS Raters and energy code professionals as it will be the benchmark for many states, counties, and municipalities moving forward.

In this post, we will review updates made in the 2024 code related to Residential Buildings and the new opportunities and challenges the code presents to builders. At the end, we provide an update on the intersection of IECC 2024 and key Energy Efficiency initiatives like ENERGY STAR and HUD loan qualifications.

Key Updates in the 2024 IECC for Residential Buildings

There are many updates from IECC 2021 to IECC 2024. Overall, the energy performance targets have gotten more challenging, but there is more flexibility in how to meet the targets.

Energy Efficiency Changes:

Changes in ceiling insulation requirements. The prescriptive attic insulation requirements have been reduced by R-11 across all climate zones (see table below).

Updates to air leakage requirements. Climate zones 0-2 and 6-8 have increased their ACH 50 stringency compared to IECC 2021.

Mechanical systems are now defined in the reference home as having the federal minimum efficiency requirements for that location. This is the first time since 2006 a project can receive credit for its mechanical system efficiency in the performance path of the IECC.

Fenestration requirements have become more stringent in cold climates.

Ventilation with energy recovery is now required in climate zones 6-8.

There are many more options for R408 Additional Efficiency Requirements in 2024. There are over 50 options for design changes that offer additional efficiency points.

The ERI path now uses ANSI 301-2022, whereas in 2021 IECC uses ANSI 301-2019. There are several new fields and calculations associated with this shift.

You can read a comprehensive overview of changes from 2021 to 2024 in this article by the National Association of Home Builders.

Pathway Requirements:

There are several ways to meet the IECC 2024 insulation requirements. What requirements your home needs to meet are determined by the code pathway your team chooses. The three pathways are Prescriptive, ERI and Performance. We will outline each of these below.

The most straightforward pathway is the Prescriptive Path which requires compliance with sections R401-R404, as well as R408. In this pathway, you can either meet the requirements in table R402.1.2 (below), or pursue the Component Performance Alternative (also called the UA alternative), where the insulation requirements are outlined in table R402.1.3 (below).

The Simulated Building Performance option requires compliance with section R405. This section is tied to the simulated annual energy use of Heating, Cooling, Mechanical Ventilation, and Water Heating of the home. This pathway can be more flexible than the prescriptive pathway, but still requires a managed overall performance of the home.

The** Energy Rating Index (ERI**) pathway requires compliance with section R406. The ERI pathway requires that the home you are building be more efficient than the IECC 2024 ERI Reference Home. There are still several prescriptive requirements outlined in R406, but overall, there is a target home that your proposed home must beat in terms of energy efficiency. All three of these pathways are programmed into Ekotrope to give your team a full set of code compliance options.

New Voluntary Appendices

Appendix RC

On-site power production can now be used to achieve an ERI target score. The target scores for projects using OPP are ERI 0.

Appendix RD

Battery storage for solar projects will now be included in the energy calculation. Battery storage will only increase the amount of energy used by the home. However, it can reduce the emissions of the home.

This appendix will not be included in Ekotrope in the initial 2024 IECC release.

Ekotrope will not support these appendices immediately. If you would like to see us support these, please reach out to info@ekotrope.com, and we can increase the priority level of supporting appendices for IECC 2024.

Benefits and Challenges for Builders

The 2024 International Energy Conservation Code (IECC) brings significant updates aimed at improving energy efficiency while providing builders with more flexibility in compliance pathways and also revised terminology.

Benefits: Increased Flexibility in Compliance

Expanded Performance Pathways: Builders can now balance building envelope improvements, mechanical system efficiency, and renewable energy integration more effectively.

Updated R408 Points-Based System: This system updates the menu of energy efficiency upgrades (e.g., advanced HVAC, high-performance windows, solar readiness) that builders can mix and match to achieve compliance. This is a much expanded version from the 5 options you had for R-408 in IECC 2021.

Electrification-Ready & Smart Controls: IECC 2024 introduces provisions for EV charging readiness, heat pump water heaters, and demand-response-ready HVAC systems, aligning residential construction with the broader shift toward grid-interactive, high-performance homes.

By expanding compliance pathways and embracing modern building technologies, IECC 2024 gives builders more tools to balance cost, performance, and compliance in ways that fit their projects.

Challenges: Adapting to New Code Requirements

While the increased flexibility and new technologies are beneficial, the transition to IECC 2024 also presents challenges, particularly in the areas of change management and complexity.

1. Change is Always Hard for Builders

New codes mean new training, new workflows, and potential disruptions to well-established construction practices. IECC 2024 offers unprecedented flexibility in energy code compliance. Helping builders navigate this complexity will be a challenge for all HERS Raters.

2. The New R408 Points System is Complex

The updated R408 points-based system introduces a significant shift in how compliance is structured. We wrote a help article on how this section of the code is implemented in Ekotrope; you can read it here. While it allows for greater flexibility, it also requires builders to:

Understand how the system works and which measures earn points.

Strategically select from efficiency upgrades to optimize compliance.

Work closely with raters and code officials to ensure that selected measures align with jurisdictional enforcement.

Since this system is entirely new, it will likely take time for builders, raters, and inspectors to fully integrate it into their workflows.

IECC 2024 and Energy Efficiency Initiatives

HUD Loans - FHA and USDA

Background:

On April 26, 2024, HUD published the final energy standards determination in the Federal Register. With this Notice, HUD and USDA adopt the 2021 IECC as the minimum energy efficiency standards for covered programs. (Source: HUD - Community Planning and Development / Environment and Energy / Minimum Energy Standards) This was a result of a statutory requirement under the Energy Independence and Security Act of 2007 (EISA) that requires HUD and USDA to jointly adopt the most recently published energy standards, subject to a cost-benefit housing “affordability and availability” test.

Implementation:

FHA-insured and USDA single-family programs will be required to implement the new standards by 18 months after the effective date of the Notice (November 2025). This has since been postponed until April 2026. The IECC requirement applies to new single-family and low-rise multifamily housing. The notice covers new construction only. Existing housing and manufactured housing are not covered by the statute.

In response to public comments, HUD and USDA made several important updates to the Preliminary Determination, including this about IECC 2024: “2024 IECC. HUD will accept the 2024 IECC or future editions of IECC as an alternative compliance path for the 2021 IECC, contingent on a final determination from DOE that the 2024 standard meets or exceeds the performance of the 2021 IECC.”

On December 20, 2024, DOE issuedits determination that the 2024 International Energy Conservation Code (IECC) will improve energy efficiency in residential buildings.

Summary

The IECC 2024 represents a significant step forward in energy efficiency, as confirmed by the Department of Energy’s determination that it delivers measurable improvements over previous codes. By incorporating innovative and flexible pathways to compliance, such as allowing efficiency upgrades to mechanical systems, IECC 2024 also seems to provide increased flexibility that builders want (NAHB Blog) to create energy-efficient homes tailored to modern demands. These enhancements not only benefit homeowners through reduced energy costs but also make it easier for homes to qualify for financing through programs like FHA and VA loans.

As communities face mounting energy supply challenges and rising utility costs, the adoption of IECC 2024 at the local level presents an opportunity to enhance the efficiency, affordability, and resilience of housing stock nationwide. To fully realize these benefits, we encourage you to explore the complete provisions of the IECC 2024, available through the International Code Council, and consider advocating for its adoption in your region.

What Do You Think?

What are your impressions of IECC 2024? What are your key questions? Which parts of IECC 2024 do you think will be the hardest to adjust to?

Share your thoughts in the comments!