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Adopting the 2021 IECC

Updated: Jun 7

Communities that regularly adopt the IECC save money for residents and businesses and improve community health and resilience. Some jurisdictions routinely augment the most recent model code with additional energy-saving code provisions or programs.

States are required to review their residential energy code and update their commercial energy code within two years of a positive determination from the Department of Energy that a new edition of the IECC saves energy.

Reasons to adopt the 2021 IECC fall into two categories: Energy Efficiency Improvements and New and updated provisions to save energy, and improve usability.

Energy Efficiency Improvements

On July 21, 2021, DOE Pacific Northwest Laboratory (PNNL) produced a final determination on the 2021 IECC representing a 9.4% site energy savings improvement and an 8.7% improvement in carbon emissions for residential buildings relative to the 2018 IECC, saving homeowners an average of $2,320 over the life of a typical mortgage.

PNNL also produced analysis on the 2021 IECC commercial provisions on September 7, 2022, finding site energy savings of 12.1% and a 10.2% GHG emissions savings for commercial buildings relative to the 2018 IECC. The determination concluded that, on a national weighted average basis, the 2021 IECC is 6.5% more efficient for site energy use and 3.3% more for energy costs than Standard 90.1-2019.

The 2021 IECC represents an approximately 40% improvement in energy efficiency for residential and commercial buildings compared to the 2006 edition, meaning that residents in states and cities on older IECC editions would see far greater savings. Improvements in the residential and commercial provisions of the IECC since 2009 will provide over 350 million metric tons (MMT) of CO2 savings for residential buildings and 340 MMT for commercial buildings, totaling nearly 700 MMT of savings. The Department has also released data on energy, cost and GHG reductions each state and many cities could achieve by adopting the 2021 IECC.

If all states updated to the 2021 IECC, nationally over 22,000 jobs would be created in the first year and over 632,000 jobs cumulatively over 30 years.

Cumulative CO2 Savings from Each Edition of the IECC (2009-2021)

Each new edition of the energy code has provided for the cost-effective reduction of energy use. Implementation of the 2021 IECC is foundational to achieving energy savings and reductions on GHG emissions across building stock, both residential and commercial. According to the US Department of Energy, from 2010 to 2040, the model energy codes for residential and commercial buildings are projected to save:

  • $138 billion energy cost savings

  • 900 MMT of avoided CO2 emissions

  • 13.5 quads of primary energy

These savings equate to the annual emissions of:

  • 195 million passenger vehicles

  • 227 coal power plants

  • 108 million homes

For perspective, the primary energy consumption of the entire U.S. commercial and residential sectors in 2020 was estimated at 38 quads.

Key changes to the 2021 IECC improve efficiency by 9.4 percent and reduce greenhouse gases by 8.7 percent over the 2018 IECC; these changes include new provisions that increase efficiency and encourage greater flexibility in design and construction as well as changes to existing requirements that provide clarification and improve usability of the code.

Additional Energy Efficient Packages

Three new additional energy-efficient package options, as shown in the figure below, were added to the 2021 IECC. This addition brings the total number of energy efficiency compliance options to eleven. The purpose of this section is to provide flexibility to achieve the energy savings needed to meet the overall energy savings goal of the code. These additional requirements come into play during the design phase where the designer has chosen the Prescriptive Compliance option. Where a designer pursues compliance via meeting ANSI/ASHRAE/IESNA 90.1 or is using the Total Building Performance approach, then Section C406 does not need to be addressed.

  • More efficient HVAC performance

  • Reduced lighting power

  • Enhanced lighting controls

  • On-site supply of renewable energy

  • Dedicated outdoor air systems

  • High-efficiency service water heating

  • Enhanced envelope performance

  • Reduced air infiltration

  • Energy monitoring system

  • Fault detection and diagnostics

  • Efficient kitchen equipment

New Tropical Climate Zone Compliance Path

Tropical areas vary from the United States mainland in climate, construction techniques and energy prices. The new Tropical Climate Zone Compliance Path recognizes traditional tropical design characteristics encompassing shading, natural ventilation and the value of cool roofs. Mainland U.S. residential construction trends can minimize fenestration area, rely on dark roofing materials and overlook the value of external shading. Applied in tropical regions, these mainland construction trends result in overheated dwellings where natural ventilation is ineffective, yet the buildings lack the insulation and air sealing appropriate for any conditioned space. Additionally, tropical electrical prices make air conditioning infeasible for many households and, likewise, provide a substantial incentive for energy conservation.

Adoptable Appendix for Net Zero Energy Buildings

The 2021 IECC includes Zero Code appendices for both residential and commercial buildings.

The residential Zero Code appendix is based on the Energy Rating Index (ERI) path of the code, which requires more efficiency than is required in the base code and requires enough onsite or offsite renewable energy production to achieve an ERI score of zero. Renewable energy compliance may happen through a combination of onsite power production, energy generated through community renewable energy facilities, and renewable energy purchase contracts or leases.

The commercial Zero Code appendix is based on the Architecture 2030 ZERO Code. It requires a building to meet the minimum code requirements, plus enough on-site or off-site renewable energy to compensate for all the energy anticipated to be consumed by the building.

The Net Zero Energy provisions included in the 2021 IECC are not mandatory unless specifically referenced in the adopting ordinance. The provisions are included as appendices with the intention to provide options for jurisdictions with ambitious climate goals.

Zero Code


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