that they would be unrealistic absent a strong state or regional role in growth management.

The prior sections have focused on the potential savings in energy use and CO₂ emissions from reduced travel associated with more compact, mixed-use development. Another important source of savings, directly related to more compact development, is the improved energy efficiency of residential buildings. The U.S. residential sector accounts for slightly more than one-fifth of the nation’s total annual energy use and produces an equivalent share of total annual CO₂ emissions (EIA 2007).²²

Substantial savings in energy use and CO₂ emissions can be achieved through improved building design, primarily by increasing the thickness of insulation and by realizing changes in home size that would result from more compact development (Kockelman et al. 2009). For example, moving from a single-family to a multifamily DU would result in significant energy savings. Calculations conducted for this study revealed that moving from a 2,400-ft² single-family home—the average home size in the United States in 2007²³—to a 2,000-ft² apartment would save about 34.1 million Btu and about 3.3 metric tons of CO₂ emissions, all else being equal (see Annex 5-1 Table 5 for detailed calculations).²⁴ By