Existing buildings require over 40% of the world’s total final energy consumption, and account for 24% of world CO2 emissions (IEA, 2006a). Much of this consumption could be avoided through improved efficiency of building energy systems (IEA, 2006a) using current, commercially-viable technology. In most cases, these technologies make economic sense on a life-cycle cost analysis (IEA, 2006b). Moreover, to the extent that they reduce dependence on risk-prone fossil energy sources, energy efficient technologies also address concerns of energy security.