When it comes to energy consumption, two — or more — can live more cheaply than one, according to a new study that blames low household density for the “overconsumption” of energy in America.

Changes in household size and home construction have been the main causes of overconsumption, said SMR Research Corp. in “Consumer Energy Spending and the Demographics of Over-Consumption.” Household demographics and home building are seldom mentioned in the debates over global warming and energy independence.

Single-person households, which have grown at triple the rate of overall population growth since 1960, use 18.4% more energy per capita than two-person households do, SMR found. They use 52.8% more energy per capita than three-person households. Even when excluding households with children, since they do not drive, per-capita energy use is far higher among single-person households than any others, SMR found.

SMR also found that people in houses with 10 or more rooms use 18.8% more energy than people in eight-room homes, and 31.3% more than people in seven-room homes — regardless of the age of the home. The average square footage of newly built homes has increased by some 34% since 1980, SMR noted.

“This study shows that energy conservationists need a new public message,” said SMR President Stuart A. Feldstein. “The old focus on things like home insulation and auto fleet mileage is incomplete. People who decide to live alone, now more than one of every four households, and people who buy the McMansions are those who squander our energy resources.”

The SMR study reviewed household spending on six major energy products: electricity, gasoline, diesel fuel, natural gas, heating oil and bottled gas. Among the findings:

The study used “micro-data” files of the Consumer Expenditures Survey, which is conducted by the Census Bureau on behalf of the Bureau of Labor Statistics. These large, complex files contain raw data on household spending on hundreds of products, allowing a researcher to isolate any product and compare spending patterns to the characteristics of families. SMR used data from 27,159 household interviews conducted in 2006 and 2007, the most recent available.

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