Residential Building Codes

Building codes for residential construction and stronger energy efficiency standards for manufactured housing can enhance energy efficiency, reduce residential utility bills, and increase health and comfort.

Table Of Contents
  1. Why This Matters
  2. Policy Solution
  3. Model Policy Features
  4. Potential Limitations & Pitfalls
  5. Complementary Policies
  6. Additional Information
  7. Examples
  8. Resources
COMMUNITY BENEFITAffordability, Housing, Public health, Resilience, Safety, Workforce
KEYWORDSDecarbonization, Efficiency, Electrification, Housing
REGIONFederal, State, Local
AFFORDABILITY STRATEGYResidential Decarbonization
OVERSIGHTEnergy Offices, U.S. Departments of Agriculture (USDA) and Housing and Urban Development (HUD), and Federal Housing Finance Agency
POLICY MECHANISMLegislation, Regulation

Why This Matters

Buildings are responsible for 40% of energy used in the US,1 and as much as 80% of a building’s energy load is subject to building energy codes.2 Increasing energy efficiency in new residential housing construction through building code updates creates opportunities for significant operational savings for all residents, including among low- and moderate-income households. According to the U.S. Census Bureau, there were approximately 1.6 million privately-owned housing units constructed in 2024.3 In addition to housing units in the pipeline, one study estimates a shortfall of 4.9 million units in 2023 in order to increase housing availability and affordability.4 As about half of the U.S. housing stock was built before 1980,5 there are significant opportunities to increase energy efficiency through existing home retrofits as well, which could cut energy use in older homes by 30 to 70 percent,6 in turn reducing energy costs and greenhouse gas emissions.


The U.S. Department of Housing and Urban Development (HUD) and the U.S. Department of Agriculture (USDA) announced the adoption of the 2021 International Energy Conservation Code (IECC) standards as the minimum energy efficiency standards for new construction funded through a number of HUD- and USDA-funded programs in 2024, but implementation has now been put on hold.7 As of 2025, 26 states also had residential codes that were less efficient than the 2018 IECC standards.8 Finally, new energy efficiency standards recently issued for manufactured housing, which is estimated to use about 35% more energy per square foot than other housing types,9 have stalled at the federal level.10 (Energy efficiency standards for manufactured housing are set at the federal level.11)

Policy Solution

State or local building codes for new residential construction and renovations, and stronger energy efficiency standards for manufactured housing at the federal level, can enhance energy efficiency, reduce residential utility bills, and increase health and comfort. Most states base their residential building codes on standards set by the International Code Council (ICC). Among the model codes developed by the ICC is the IECC, which is updated every three years.12 As concerns have been raised about the industry influence and process abnormalities in the development of the 2024 IECC standards,13 state adoption of the 2021 IECC is recommended at this time. 


The energy cost savings of state adoption of the 2021 IECC standards is significant. Compared to 2018 IECC standards, adoption of the 2021 standards is expected to result in an estimated energy cost savings of about 8.7% nationally14 or life-cycle cost savings of $2,320 per dwelling.15 The average payback period for the 2021 standards is estimated to be 10.5 years.16 For those states with the 2009 IECC standards in place, adoption of the 2021 IECC standards could result in a 27% decrease in residential energy use and over $14,000 in cost savings over the life cycle of the home.17

Model Policy Features

State and local measures to improve the energy efficiency of new residential construction, retrofits, and manufactured homes, thereby reducing operational costs for residents, include:

  • Adoption of the 2021 IECC standards for new residential construction.
  • Enactment of “stretch codes”—which could be encouraged through additional incentives, be enacted by local government, or apply to specific building types—such as:
    • Require solar panels and heat pumps in newly-constructed homes.
    • Include elements from the 2021 IECC optional “Zero Energy Home appendix” for enhanced energy efficiency.18
    • Incorporation of demand response technology.19 
    • Encourage existing air conditioners to be replaced with heat pumps at burn out.20
  • Regular code compliance reviews (at least every five years), using standardized tools and a statistically significant sample.21
  • Inclusion of high road jobs and training or apprenticeship opportunities, including strategies to reach underemployed communities.
  • Applies to home renovations and remodels to bring such projects up to the standards contained in the updated codes.
  • At the federal level, strategies to improve efficiency include reinstatement of the 2021 IECC standards by HUD and the USDA, implementation of the 2022 energy efficiency standards for manufactured homes, and requirement by the Federal Housing Finance Agency (FHFA) that home mortgages for new construction backed by Fannie Mae and Freddie Mac, which are administered by FHFA, conform to the 2021 IECC standards.22

Potential Limitations & Pitfalls

  • The average payback period for the 2021 standards, estimated to be 10.5 years, may be viewed as onerous to some homeowners; some homeowners may opt to forgo energy efficiency upgrades through retrofits and/or purchase less efficient homes to reduce upfront costs.23

Complementary Policies

Complementary policies that can improve the effectiveness of residential building codes include:

  • Residential solar (+storage) programs increase home decarbonization and improve resilience.
  • Limiting gas infrastructure investments would facilitate the transition to clean energy in residential construction while also limiting costs for gas infrastructure that are passed on to other residents. 
  • Rental efficiency standards to improve the energy efficiency of rental units and decrease the energy burdens of tenants

        Additional Information

        As of 2025, however, only nine states have adopted the 2021 IECC residential standards or the equivalent.24

        Examples

        1. California 2025 Building Energy Efficiency Standards (Title 24) – Restructured 2025 Energy Code – California Code of Regulations – Title 24, Part 6

        Details:

        • Increases use of heat pumps for space and water heating in new construction.25 
        • Encourages electric-ready buildings.26  
        • Updates solar photovoltaic and battery energy storage system standards in multifamily buildings.27 
        • Applies Building Energy Efficiency Standards to manufactured homes.28
        • Improves ventilation requirements in multifamily buildings.29
        • Incorporates or exceeds 2021 IECC building envelope elements.30
        • Expected to result in a reduction of $4.8 billion in energy costs and approximately 4 million metric tons in greenhouse gas emissions.31

        LIMITATIONS:

        • Enactment of AB 130 in California excludes residential building code updates from the next round of Title 24 updates and prevents local code upgrades, with a few exceptions, because of housing affordability concerns.32

         2. 2024 Vermont Residential Building Energy Standards (RBES) – Vermont Residential Building Standards (RBES): Energy Code Handbook

        Details:

        • Includes elements of the 2021 and 2024 IECC standards, as well as additional requirements.
        • Includes base and optional stretch codes.
        • Stretch code includes installation of a “solar-ready zone” for single-family homes, duplexes, and townhouses (e.g., requiring that 40% of the roof be available for panels, square footage requirements on the property that be preserved for solar, exclusive of setbacks).
        • Applies to manufactured homes that are not on a permanent chassis.
        • Includes specific requirements for renovations of existing homes.
        • Includes requirements for electric vehicle charging parking spaces and/or stations for multi-family buildings.

        LIMITATIONS:

        • In September 2025, Governor Phil Scott issued Executive Order 06-25 granting the option of compliance with Vermont’s 2020 Residential Building Energy Standard rather than the 2024 standards, charging that the 2024 standards were having a detrimental impact on the state’s housing supply and housing affordability.33

        Resources

        • For the status of energy codes by state, see:
          • U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Building Energy Codes Program. State Portal. Accessed: August 4, 2025.

        Written: November 2025

        1. Shoemaker, S. (2023). NREL Researchers Reveal How Buildings Across United States Do—and Could—Use Energy. National Renewable Energy Laboratory. ↩︎
        2. U.S. Department of Energy, Office of Energy Efficiency & Renewable Energy. Why Building Energy Codes? Accessed: November 25, 2025. ↩︎
        3. U.S. Census Bureau. New Residential Construction: Annual and Monthly Data, Housing Units Completed, last revised June 18, 2025.  ↩︎
        4. Patel, E., Rajan, A., and Tomeh, N. (2024) Make it count: Measuring our housing supply shortage. Brookings Institution. ↩︎
        5. U.S. Census Bureau, 2023 American Community Survey 5-Year Estimates. DP04: Selected Housing Characteristics. Accessed: July 21, 2025. ↩︎
        6. Martín, C. (2022). What Strategies are Needed to Implement Energy Retrofits Equitably and Practically? Joint Center for Housing Studies of Harvard University. ↩︎
        7. U.S. Department of Housing and Urban Development. Minimum Energy Standards: Adoption of Energy Efficiency Standards for New Construction of HUD- and USDA-Financed Housing – Final Determination, as of March 27, 2025.  ↩︎
        8.  U.S. Department of Energy, Office of Energy Efficiency & Renewable Energy. (2025.) State Portal. ↩︎
        9. U.S. Energy Information Administration. (2018). 2015 Residential Energy Consumption Survey: Energy Consumption and Expenditures Tables, Table CE1.1 Summary annual household site consumption and expenditures in the U.S.—totals and intensities, 2015. ↩︎
        10. U.S. Department of Energy. (2025). Energy Department Issues Final Rule Delaying Compliance Deadline for Manufactured Housing Standards. ↩︎
        11. Federal Register. (2025). Energy Conservation Standards for Manufactured Housing. ↩︎
        12. Climate XChange. Buildings and Efficiency: Residential Energy Codes. State Climate Policy Dashboard. Accessed: July 17, 2025.  ↩︎
        13. American Council for an Energy-Efficient Economy. (2024). International Code Council Caves to Special Interests, Axes Decarbonization Measures from Model Building Code.  ↩︎
        14. Salcido, V.R., Chen, Y., Xie, Y., and Taylor, Z.T. (2021). Energy Savings Analysis: 2021 IECC for Residential Building. Pacific Northwest National Laboratory. ↩︎
        15. Salcido, V.R., Chen, Y., Xie, Y., and Taylor, Z.T. (2021). National Cost Effectiveness of the Residential Provisions of the 2021 IECC. Pacific Northwest National Laboratory.  ↩︎
        16. Salcido, V.R., Chen, Y., Xie, Y., and Taylor, Z.T. (2021). National Cost Effectiveness of the Residential Provisions of the 2021 IECC. Pacific Northwest National Laboratory.  ↩︎
        17. Sherman, E. (2023). Pathways to Equity and Savings for Low-Income Households. RMI. ↩︎
        18. Cheslak, K. (2020). The New Residential Zero Energy Appendix: An Important Addition for Code Adoption. New Buildings Institute. ↩︎
        19. Salcido, V., Chen, Y., Taube, B., Franconi, E., and Rosenberg, M. (2021). Demand Response in Residential Energy Code. ↩︎
        20. California Energy Codes & Standards, Reach Code Paths: Electrification. Accessed: November 25, 2025. ↩︎
        21. Kresowik, M., Subramanian, S., Specian, M., Bradley-Wright, F., Ghosh, D., Mooney, P., Fraser, A., Sosa-Kalter, S., Fadie, B., and Mauer, J. (2025). The 2025 State Energy Efficiency Scorecard. American Council for an Energy-Efficient Economy. ↩︎
        22. Just Solutions. (2025). An Immediate Opportunity to Modernize Residential Energy Codes for a Resilient Future. ↩︎
        23. Salcido, V.R., Chen, Y., Xie, Y., and Taylor, Z.T. (2021). National Cost Effectiveness of the Residential Provisions of the 2021 IECC. Pacific Northwest National Laboratory.  ↩︎
        24. U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Building Energy Codes Program. State Portal. Accessed: August 8, 2025. Michigan adopted the 2021 IECC standards in 2025, but implementation has been put on hold pending a lawsuit from the building industry. (Smolcic Larson, L.
          [2025]. Michigan agrees to delay new home construction codes amid builder lawsuits. MLive.)  ↩︎
        25.  California Energy Commission. (2024). Energy Commission Adopts Updated Building Standards Expanding Requirements for Heat Pumps and Electric-Ready Buildings; California Energy Commission. 2025 Building Energy Efficiency Standards. Accessed: July 21, 2025. ↩︎
        26. California Energy Commission. (2024). Energy Commission Adopts Updated Building Standards Expanding Requirements for Heat Pumps and Electric-Ready Buildings; California Energy Commission. 2025 Building Energy Efficiency Standards. Accessed: July 21, 2025. ↩︎
        27. California Energy Commission. (2024). Energy Commission Adopts Updated Building Standards Expanding Requirements for Heat Pumps and Electric-Ready Buildings; California Energy Commission. 2025 Building Energy Efficiency Standards. Accessed: July 21, 2025. ↩︎
        28. Legal Information Institute, Cornell Law School. Cal. Code Regs. Tit. 25, § 4369 – Energy Requirements. ↩︎
        29. California Energy Commission. (2024). 2025 California Energy Code: Fact Sheet; M. Borgeson. (2024). California Code Takes Another Step Toward Clean Buildings. Natural Resources Defense Council. ↩︎
        30. U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Building Energy Codes Program. State Portal. Accessed: August 4, 2025. ↩︎
        31. California Energy Commission. (2024). Energy Commission Adopts Updated Building Standards Expanding Requirements for Heat Pumps and Electric-Ready Buildings ↩︎
        32. Takemura, A.F. (2025). California halts building code updates in a blow to electrification. Canary Media. ↩︎
        33. State of Vermont, Executive Department. (2025). Executive Order No. 06-25. 
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