To limit the probability that the effective thermal resistance of above-ground opaque building envelope assemblies and components will be overly reduced in the trade-off calculations, which could lead to trade-off calculations creating building envelope conditions that are beyond the limits of the trade-off model, which could lead to the trade-off model using more energy than the prescriptive reference, which could lead to excessive thermal transfer through the building envelope, which could lead to excessive use of energy for heating and cooling, which could lead to an unacceptable effect on the environment.