Generally, the envelope of a structure is designed by architects to respond to many considerations, including structural and esthetics. Before the oil crisis of 1973, the energy e—ciency of the envelope components was rarely considered as an important factor in the design of a building. However, since 1973 several standards and regulations have been developed and implemented to improve the energy e—ciency of various components of building envelopes. For energy retro‘t analysis, it is helpful to determine if the building was constructed or modi‘ed to meet certain energy e—ciency standards. If this is the case, retro‘tting of the building envelope may not be cost-ešective. However, improvements to the building envelope can be cost-ešective if the building was built without any concern for energy e—ciency, such as the case with homes constructed with no insulation provided in the walls or roofs.