International Energy Conservation Code (IECC)
The International Energy Conservation Code (IECC) developed by the International Code Council (ICC) is one part of a suite of model construction codes known at the I-Codes. The IECC is a model energy code that sets minimum efficiency standards in new construction for a structure’s walls, floors, ceilings, lighting, windows, doors, duct leakage, and air leakage. It is the most adopted energy code in the country for homes and is also recognized as the national model energy code for low-rise residential buildings in federal law.
IECC Development
ICC published the 2024 edition of the IECC on August 14, 2024. Historically, the IECC has followed the same code development process as other model building codes. Beginning with the 2024 IECC, ICC changed the procedures so that it now follows a standards development process, where the final decisions rest with consensus committees, not governmental voting members. Now, two consensus committees – one for the commercial provisions and one for the residential provisions – are tasked with updating the energy code.
NAHB was represented on both committees by a small group of NAHB builder members and NAHB staff who devoted significant time and effort to ensure the new energy will prioritize cost-effectiveness and consumer benefits, maximize design choices for builders, and can be practically implemented in the field. These individuals continue their work on these bodies to develop the next edition of the code, the 2027 IECC.
IECC Adoption
When a state or jurisdiction goes through the adoption process for any building codes, including energy codes, there are typically public hearings, comment periods, and an opportunity to suggest amendments the model codes. NAHB offers resources through a series of code adoption kits to help builders and state and local HBAs navigate the new requirements of recent IECC editions. These resources include a list of significant changes from the previous code version, estimates of added construction costs, a list of suggested amendments, and more. Contact the NAHB Construction Codes and Standards staff member in your area for assistance.
As states and local jurisdictions consider updates to their energy codes in the coming years, the 2024 IECC will be one of several options available. It is crucial for builders to understand the major differences in the requirements and format of the 2024 IECC compared to its previous editions (the 2021 IECC and 2018 IECC). NAHB broadcast a members-only webinar overview of the 2024 IECC. Learning about the code usability improvements of the 2024 IECC and their cost implications for residential construction will empower builders to assist their state and/or local HBA to frame the discussion on energy code adoption in their jurisdiction.
Energy Code News from NAHB
NAHBNow, the official news blog of NAHB, is your one-stop source for home building industry news, product information, and educational resources. Bookmark NAHBNow for the latest NAHB news on energy codes.
Energy Code Determinations - Department of Energy
After a new edition of a model energy code (the IECC and ASHRAE Standard 90.1) is published, the U.S. Department of Energy compares the latest edition of the code to the previous edition to determine if the new code is more energy efficient. For example, in December 2024 DOE issued a determination on the 2024 IECC showing that it achieves a 7.8% site energy savings and 6.6% energy cost savings compared to the previous edition, the 2021 IECC. A positive determination by DOE triggers a series of requirements that are outlined in the DOE Energy Code Determinations State Certifications fact sheet from NAHB.
Energy Code Cost Analysis
The cost-effectiveness of various energy efficiency measures included in recent IECC editions ranges widely. As a model energy code, the IECC is intended to be reviewed and evaluated by adopting states and local jurisdictions who are empowered to amend the code to better fit their specific conditions.
NAHB publishes cost-effectiveness analyses conducted by Home Innovation Research Labs and other compliance costs estimates. All information in these resources is based on the unamended provisions of the model energy codes being analyzed.
- 2024 IECC Cost Effectiveness Analysis
- Cost of Compliance with Recent Model Energy Codes: 2021 IECC & 2024 IECC
- 2021 IECC Residential Cost Effectiveness Analysis
- Note about 2015 IECC and 2018 IECC: There were no significant cost increases between these two editions and their predecessor 2012 IECC, so no formal analyses were published
- 2012 IECC Cost Effectiveness Analysis
- 2009 IECC Cost Effectiveness Analysis
- Methodology for Calculating in Residential Buildings
- National Multifamily Housing Council resources:
Energy Code Adoption by State
NAHB provides a summary of state residential energy code provisions adopted by each of the 50 U.S. states, the District of Columbia, and Puerto Rico. Many states also choose to amend the model code to address local conditions. Information on the most impactful amendments (if applicable) as compared to the model code edition adopted by the state are included in each listing, which also provides the effective date of the state’s most recent code update plus links to the adopted code language and relevant state adoption authority.
Several states do not adopt any mandatory statewide residential energy code (typically referred to as “home rule” states), though there are often codes adopted by local jurisdictions (which are generally not reflected in this document). Some states choose to develop their own energy codes that are not based any edition of the IECC. This summary document does not cover the commercial (or nonresidential) energy code provisions adopted by states or jurisdictions.
Coming soon: NAHB will publish a detailed catalogue of the model energy codes adopted and amended at the state and local level throughout the country along with information about the processes and governmental bodies that update these codes. This resource will connect state and local HBA staff and members to the policymakers in their area to help them more effectively advocate for NAHB's Housing Policy Priorities.