Washington ? Houses built now are bigger, but they’re on smaller lots. More people are living in the suburbs, but not necessarily in a house with a yard. And the typical American home these days is constructed with more bathrooms, more bedrooms and more amenities than in the past – but on average shelters fewer people.

Using Census data to examine housing patterns of the past 30 years reveals not wholly surprising changes in measures such as popular home styles and where people have settled. But the numbers also yield insights into the rate at which the size of homes have grown and why.

Traditionally, middle-class homeowners have purchased larger houses to accommodate the need for more space – a growing family, for example. But the past three decades have seen homes grow not because they need to, but simply because they can.

From 1975 to 2005, the average size of new single-family homes grew by 48 percent, according to the Census Bureau’s 2005 survey of new housing, released this summer. That happened even as the typical household has gotten smaller, falling from 2.94 people in 1975 to 2.6 people in 2004, the latest figure available. At the same time, the lots that the houses stand on have shrunk by about 13 percent.

The desire to trade up has been fueled by the growth in personal income in the 1990s. That put more shoppers in a position to afford bigger homes and amenities such as central air conditioning, outdoor patios and three-car garages.

“Americans generally seem to like to supersize everything, whether it’s houses or cars or TV sets or hamburgers,” said John McIlwain, the senior fellow for housing at the Urban Land Institute. “So if you can afford it, more people will buy bigger even if you don’t need it.”