Cavity insulation limits conductive heat flow in the majority of the wall. The framing, however, will conduct heat at a greater rate than the insulation, creating, in effect, a "thermal bridge." (photo: Jonathan Tauer)
Continuous insulation (CI) is added to the exterior to limit the conductive heat losses through the framing. (photo: Ted Cushman)
In this selection from the energy code, we can think of different climate zones as representing varying temperature differences. In colder climates (zones 4 and above), the temperature differences in winter between indoors and outdoors are greater, so conductive heat flows at a greater rate through building assemblies. To limit this heat flow, more insulation is needed. Note that the “ 5” R-values indicate continuous insulation that insulates against heat flowing across wall studs, while the other numbers indicate cavity-insulation R-values.
Conductive heat loss around the perimeter of insulated glass units (dark areas in the thermographic image, left) caused by metal edge spacers. To avoid such losses, window makers may use“warm-edge” nonmetal spacers, such as the PPG Intercept (right).