On the residential side, this energy was used in approximately 80.8 million single-family homes, 24.8 million multifamily housing units, and nearly 6.9 million mobile homes in the United States as of 2006 (EIA, 2008b). On the commercial side, there were approximately 75 billion square feet (7 billion square meters) of floor space in 5 million commercial buildings as of 2006 (EIA, 2008b). The building stock is long-lived: homes can last 100 years or more, commercial buildings often last 50 years or more, and appliances and equipment used in buildings can last 10–20 years (IWG, 1997). Nonetheless, there have been significant changes in energy use and energy efficiency in buildings over the past 30 years.

Energy use in buildings has increased over the past 30 years, but at a rate slower than the rate of increases in gross domestic product (GDP). As shown in Figure 2.3, in the residential sector over the period 1975–2005, delivered-energy

FIGURE 2.3 U.S. residential energy use trends. Primary energy use (accounting for losses in electricity generation and transmission and distribution, and for fuels, such as natural gas, used on-site) has increased faster than delivered energy use (which does not account for such losses, but does include fuels used on-site) because use of electricity has increased faster than use of other fuels.

FIGURE 2.3 U.S. residential energy use trends. Primary energy use (accounting for losses in electricity generation and transmission and distribution, and for fuels, such as natural gas, used on-site) has increased faster than delivered energy use (which does not account for such losses, but does include fuels used on-site) because use of electricity has increased faster than use of other fuels.

Source: Data from EIA, 2007b.



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