IECC
The IECC (International Energy Conservation Code) is the model energy code published by the International Code Council and adopted (often with state-level amendments) by most US jurisdictions. The IECC sets minimum requirements for building envelope R-values, fenestration U-factors, mechanical equipment efficiency, and lighting power density. New IECC versions are released every 3 years; states adopt them on different schedules — some use the latest, some are years behind.