My REScheck project complied with the 2003 IECC. Why does it fail under the 2006 IECC?
The 2006 IECC was completely redesigned, and several of the new code characteristics may cause your house to fail. The most important difference between earlier editions and the 2006 IECC is that envelope requirements are not coupled to the home’s glazing area percentage. A home with modest glazing area, say 13% of floor area, will likely require a more efficient envelope for 2006 IECC compliance. Conversely, a home with larger glazing area, say 20% of floor area, may achieve 2006 IECC compliance with less insulation. The 2006 IECC also implements a revised climate zone system. The revised system introduced more homogeneity across climates, resulting in less variation in the envelope requirements from location to location. Therefore, some locations have slightly different (higher or lower) efficiency requirements under the 2006 IECC than under the previous codes.
