2021 IECC National Model Energy Code (Base Codes)

Codes And Policy / Energy Codes

After about a decade with few meaningful updates to the IECC, the 2021 improvements are poised to help the code catch up to modern-day building technology and practices, reducing millions of tons of carbon from entering the atmosphere while reducing energy bills for tenants, homeowners, and business owners. NBI worked with partners and built on past success in the IECC process to support achievement of the important efficiency gains in the IECC. The 2021 code also includes a Zero Energy Homes Appendix which provides cities and states an opportunity to include zero energy building performance as a stretch code and illustrates what is within reach for the next code update. For more details about how the 2021 IECC was developed, read our blog: The 2021 IECC’s Circuitous Path to Conclusion.

Want the latest IECC information? Follow our updates on the 2024 IECC process.

2024 IECC Code Change Proposal Synopsis

FINAL STATUS OF THE 2021 IECC: After an extended period of appeals the 2021 version of the International Energy Conservation Code (IECC) was approved . DOE has determined that the residential energy code resulted in a 9.38% savings over the previous version. 

After the approval of the 2021 IECC, the International Code Council (ICC) began consideration of a change to the development process that would take the voting power away from jurisdictions and put it in the hands of a small committee. In March 2021, the ICC announced a new framework that changed the essential nature of the IECC development process from a model energy code to a standard. 

NBI opposed this outcome and testified against it during an ICC Board of Directors meeting on this proposed change in January. Read our press release on the ICC decision for details  


The proposals cover a wide range of measures and improve the code by adding additional efficiency, clarifying requirements and creating greater flexibility for code users and local jurisdictions.

Proposals are organized here by Residential and Commercial. Each item provides a synopsis of approved proposals categorized by building system. Individual code change proposal numbers that contributed to savings for each building system are provided in brackets [ ]. Any questions on finding final language can be sent to us by email.

Residential Buildings | Code Change Proposals are also available here by number.

Building Envelope
Increases in ceiling R-values in Climate Zones 2 thru 8. Requires continuous insulation for walls in Climate Zones 4 and 5. Requires slab edge insulation in Climate Zone 3 and increases the R-value and depth of slab edge insulation in Climate Zones 4 and 5 [RE29, 32, 33, 36]. Increases the fenestration U-factor requirements in Climate Zones 2 thru 4 [RE35]. Increases the stringency of SHGC requirements in Climate Zone 4 and added a SHGC requirement in Climate Zone 5 [RE37].

HVAC Systems
Ducts are now required to leakage tested in unconditioned and condition spaces [RE112]. Ventilation systems that are part of whole house ventilation system are required to be tested to verify that they meet the minimum CFM rates [RE130]. Ventilation fan efficacy has increased to meet the current Energy Star standards [RE133]. Energy recovery ventilation or heat recovery ventilation is required in Climate Zones 7 and 8 [RE139].

Lighting and Power
Increases the lighting efficacy requirements for dwelling unit lighting to encourage the use of LED lighting and requires lighting controls to dim or automatically turn lights off [RE7, 145].  Exterior lighting for multifamily buildings will meet exterior lighting requirements for commercial buildings [RE148].

ERI Approach
Increases the efficiency of the ERI values to the IECC 2015 level. Places a limitation on the use of renewables that can be counted toward compliance with the IECC [RE 192, 184].

Flex Packages
Requires that those complying with the prescriptive or simulated performance path also comply with one Flex Package containing additional efficiency measures. Those complying with the ERI must be 5% more efficient than the ERI score [RE209].

Revises the definition for “on-site renewables” for consistency with other national standards. Adds definition for biogas and biomass [CE31]. Requires that Renewable Energy Certificates (RECS) be retired with the homeowner when using the ERI compliance approach [RE 204].

ZE Appendix
Provides a zero energy appendix that requires compliance with an ERI score without considering renewables and then achieving a score of “0” with renewables [RE223]. This new appendix in the 2021 IECC will provide every jurisdiction an opportunity to adopt a base or stretch code that achieves zero energy in homes and low-rise multifamily buildings. To learn more about the Zero Energy Appendix for the 2021 IECC, read our factsheet.

Commercial Buildings | Code Change Proposals are also available here by number.

Building Envelope
The Above grade wall definition has been revised to include the exposed edges of mid floor slabs as part of aan above grade wall [CE35]. Below grade wall, mass floor and slab perimeter insulation R-value requirements increased in Climates Zones 4 to 8. Framed floor insulation also increased Climate Zone 1 and 6 to 8 [CE61, 63, 64, 66, 68]. Building orientation fenestration requirements have been replaced with requirements for fixed and operable fenestration SHGC [CE87]. Air barrier testing leakage testing is now mandatory for many building types, sizes and climate zones. Air barrier verification is required for all buildings that are not tested for air barrier leakage. [CE96, 97, 99]

HVAC Systems
Updates the equipment efficiency requirements to those contained in ASHRAE 90.1-2019. [CE113]. Requires fault detection and diagnostics for systems in buildings over 100,000 ft2. [CE111]. Energy recovery ventilation is required for all non-transient dwelling units greater than 500 ft2. [CE133]. Requires fans less than 1/12 hp to meet minimum fan efficacy requirements [CE140 PC1].

Service Water Heating
Increases the thermal efficiency, Et, requirements for service water heating equipment 1,000,000 Btu/h or greater [CE156].

Lighting and Power
Increases the lighting efficacy requirements for dwelling unit lighting to encourage the use of LED lighting [CE162]. Requires controls for parking lot lighting that will dim the lights when no activity is detected and that will dim the lights if adequate daylight is present [CE199]. Requires corridor lighting to be controlled by occupancy sensors [CE169]. Adds requirements for controls that automatically turn off receptacles [CE216]. Requires metering for buildings 25,000 ft2 and great and for six end use categories [CE215]. Reduces the allowed lighting power density W/ft2 values for whole building and space-by-space [CE206, 208]. Places requirements on lighting used for indoor plant growth [CE209].

Additional Efficiency Packages
Replaces the C406 Additional Efficiency Packages with a points based format based on occupancy type, climate zone and measure. Also adds credit for commercial kitchen appliances, energy monitoring systems and fault detection and diagnostics [CE218, 226, 237, 239, 240]

Revises the definition for “on-site renewables” for consistency with other national standards. Adds definition for bi gas and biomass [CE21, 31].

Appealed Proposals | Code Change Proposals available by number for residential and commercial

The following proposals were accepted into the code by Governmental member voting, remained intact through the challenge process, but ultimately were removed from the code by the ICC Board during the appeals process:

Residential Buildings:

Water Heating
NAECA minimum electric storage tank water heaters are required to be installed with renewables. Gas water heating is required to meet the minimum UEF [RE126]. Requires water heating systems using gas to not contain continuously burning pilot lights [RE107].

Lighting and Power
Electrical outlets required by all fossil fuel appliances [RE147].

Electric Vehicle Ready
Requires EV Capable or Ready charging stations for residential buildings [CE217].

Commercial Buildings:

Lighting and Power
Requires EV Capable or Ready charging stations for high rise residential and commercial buildings [CE217].