Commercial Envelopes (Business Case for Retrofitting Buildings) (Reprint‪)‬

More than 5 million buildings, totalling more than 80 billion [ft.sup.2] (7.4 billion [m.sup.2]) of floor space, comprise the U.S. commercial building stock. Eighty percent of these buildings will still be in operation for at least the next two decades. These inefficient buildings will continue to waste energy unless improved. (1,2) Commercial building retrofits occur at a rate of 2.2% of the current stock per year, or approximately 2 billion [ft.sup.2] (185 million [m.sup.2]) per year. (3) The commercial building sector consumed 18% of the annual primary energy consumed in the U.S. for 2010. (4) This energy primarily fuels lighting (up to 30% of consumed energy) and HVAC (up to 40% of consumed energy). Both are forced to use more energy due to envelope air infiltration, and heat and light gain and loss through windows.