You understand a building's roof assembly serves an important role in improving the building's overall energy efficiency and reducing building owners' heating and cooling costs. However, you may not realize codes mandate minimum thermal insulation requirements for the energy efficiency of most buildings and, in some instances, these minimum R-values may be more than you are accustomed to providing.
Energy conservation codes usually are adopted by states and apply to all buildings in a state. Most states have adopted one of several editions of the International Energy Conservation Code (IECC), published by the International Code Council (ICC), to serve as the technical basis of their energy codes. In some instances, states modify IECC to address specific regional or local issues.
In several instances, jurisdictions or cities may adopt an energy code that is different from the state-adopted code. For example, Chicago has developed and maintains an energy conservation code that is somewhat different from Illinois' state energy conservation guidelines. However, Chicago's energy conservation code still is loosely based on IECC.