SAN FRANCISCO — In what is said to be the first United States study to measure the real impact of building energy codes on total household energy consumption, the Climate Policy Initiative (CPI) found that U.S. building energy codes have reduced household energy use and greenhouse gas emissions. The study also found that states adopting these codes, which encourage the use of highly efficient natural gas heating equipment and electric heat pumps, shifted their energy use away from oil and wood fuels towards lower-emissions natural gas.

Residential buildings consume 22 percent of U.S. primary energy use and produce 21 percent of U.S. carbon dioxide emissions, said CPI, so the ultimate potential impact of building energy codes is substantial. Most states have adopted U.S. Department of Energy (DOE)-recommended model codes, first set in 1992 and subsequently updated several times; others have written their own standards. Seven U.S. states — Alabama, Mississippi, Missouri, North Dakota, Oklahoma, South Dakota, and Wyoming — do not have mandatory building energy codes. Other states such as New Mexico and Maine are considering reverting to less stringent codes.

CPI’s analysis, which reviewed states’ energy use from 1986 to 2008, found that states adopting federal codes have achieved an approximately 10 percent reduction in household energy use, and a 16 percent reduction in household greenhouse gas emissions.