IECC (International Energy Conservation Code)
The model energy code most U.S. states use as the basis for building energy rules.
Quick Answer
The International Energy Conservation Code (IECC) is a model code published by the International Code Council that sets minimum energy efficiency requirements for residential and commercial buildings. It covers the envelope, mechanical, lighting, and power systems, and states and cities adopt it, often with amendments, as the basis for their energy codes.
The Full Picture
The IECC is part of the International Codes family, alongside the IBC. The International Code Council updates it on a three-year cycle, and each state or local jurisdiction decides which edition to adopt and what amendments to apply. As a result, two neighboring jurisdictions can enforce different editions of the code.
The code is split into residential and commercial parts. Residential provisions apply to one- and two-family dwellings and low-rise multifamily buildings of three stories or fewer. Commercial provisions apply to other buildings, and they include an alternative path allowing compliance with ASHRAE Standard 90.1 instead of the IECC's own commercial requirements.
Requirements are organized by climate zone and cover building envelope insulation and fenestration, air leakage, mechanical system efficiency, service water heating, electrical power and lighting controls, and in newer editions additional efficiency measures and renewable energy provisions. Compliance can be demonstrated through prescriptive requirements, performance simulation, or other approved methods.
The U.S. Department of Energy tracks state adoption of energy codes and publishes determinations on how code editions affect energy savings. For contractors, the adopted edition influences insulation, glazing, air barrier, lighting control, and HVAC scope, so confirming which version applies early helps avoid pricing surprises.
Real Examples
Common Misconceptions
People assume: The IECC applies nationwide automatically.
Actually: It is a model code. It applies only where a state or local government adopts it, and the edition and amendments vary.
People assume: The IECC and ASHRAE 90.1 are competing codes, so projects must pick one before design.
Actually: For commercial buildings the IECC accepts 90.1 as an alternative path. The jurisdiction's rules determine which paths are allowed.
Does MeltPlan Solve This?
Partially — adjacentMeltPlan Code can help teams research the energy code requirements that apply to a project and surface possible compliance gaps. It does not run energy models or issue compliance determinations.
Research energy code requirements →Frequently Asked Questions
Who publishes the IECC?
The International Code Council, which updates the code on a three-year cycle.
How is the IECC adopted?
State or local governments adopt a specific edition, often with amendments, through legislation or rulemaking.
Does the IECC cover commercial buildings?
Yes. It has separate residential and commercial provisions, and the commercial side allows ASHRAE 90.1 as an alternative compliance path.
What are climate zones in the IECC?
Geographic classifications, based on temperature and moisture, that determine the prescriptive insulation and fenestration requirements for a location.
Where can I find which IECC edition my state uses?
The U.S. Department of Energy's Building Energy Codes Program tracks state adoption, and the local building department confirms current requirements.