International Energy Conservation Code, 2021 Edition: Developed and published by the International Codes Council “establishes minimum regulations for energy efficient buildings using prescriptive and performance‐related provisions. This code is founded on principals intended to establish provisions consistent with the scope of an energy conservation code that adequately conserves energy; provisions that do not unnecessarily increase construction costs; provisions that do not restrict the use of new materials, products or methods of construction; and provisions that do not give preferential treatment to particular types or classes of materials, products or methods of construction.” The IECC allows for three different methods to gain approval for the Building Envelope. These methods are: Prescriptive approach, Trade-offs, and the Performance approach.

Prescriptive Approach: The code option in which particular measures are required, such as specific air sealing characteristics and insulation levels or R-values. Under the prescriptive approach, these R-values are set by using the climate zone chart and are minimal requirements. The State of Illinois has adopted (1/1/23) the 2021 IECC now requiring  R30 for walls or R25 in the cavity and R5 to the exterior and now R60 in the attics/ roof.  This is THE MOST COMMON METHOD USED FOR DRAWINGS AND IS LIKELY THE ONLY METHOD FAMILIAR TO YOUR LOCAL CODE OFFICIAL!

Trade-offs: This method of evaluation allows some degree of design flexibility based upon trading-off efficiency of key building components. An example would be to use less insulation in an Attic assembly when using a higher efficiency heating system. The Res-check program is commonly used to gain compliance with the trade-off method. Slightly more sophisticated than the prescriptive approach but not nearly as sophisticated as REM Design due to the lack of taking into account the air sealing impact of foam!