The U.S. Census Bureau has been collecting detailed information on household size since 1940 and tracking certain characteristics of houses since 1963. Data on houses were collected by the U.S. Department of Housing and Urban Development and other agencies from 1940 to 1963. Average household size in the United States has dropped steadily from 3.67 members in 1940 to 2.62 in 2002. The average size of new houses increased from about 1,100 ft2 (100 m2) in the 1940s and 1950s to 2,340 ft2 (217 m2) in 2002. Factoring together the family size and house size statistics, we find that in 1950 houses were built with about 290 square feet (27 m2) per family member, whereas in 2003 houses provided 893 square feet (83 m2) per family member (NAHB 2003) -- a factor of 3 increase.
Other trends in American single-family housing have been similar. In 1967, for example, 48% of new single-family houses had garages for two or more cars; by 2002, that figure had jumped to 82%. In 1975, 20% of new single-family houses had 2.5 or more bathrooms; by 2002, that figure had increased to 55%. In 1975, 46% of new houses had central air conditioning; by 2002, 87% had it.
Quoted from the Small is Beautiful: U.S. House Size, Resource Use, and the Environment