In the last few years a lot of attention has been placed on the proper installation of continuous insulation in buildings. The purported reason for this has been to stop the thermal bridging that occurs when you put thermal insulation between steel studs.
Years ago, we started out insulating our buildings by requiring a certain R-Value insulation to be installed in the cavities. In those days wood framing was very common. As we moved to steel studs in commercial buildings, we realized that the building assembly was performing less than the R-value of the insulation. From that we started requiring an “effective thermal insulating value”.