What it means. The first decade of the new millennium had been a time of outsize appetites in this country—witness bulging waistlines, gas-guzzling SUVs, and massive mortgages. Also on the housing front, oversize homes epitomized the too-much-of-everything-is-just-enough culture.

Today, just as our thirst for large cars and loans have slaked—you probably can't say the same about our eating habits—home design has entered an era of moderation. Rightsizing, in which houses are appropriately scaled to the needs of their occupants, is the keyword of the moment.

Why the buzz? Rightsizing was a major theme of the 2009 International Builders' Show, held last month in Las Vegas. On January 21, Gopal Ahluwalia, vice president of research for the National Association of Home Builders, led the "Consumer Preferences 2009" seminar. As part of his talk, Ahluwalia presented a graph showing a dip in the size of homes started in the third quarter of 2008 compared with those started in the second quarter last year: The average floor area shrank almost 200 square feet—from 2,629 to 2,438—while the median floor area fell from 2,291 to 2,090, according to Ahluwalia. He also revealed that 88 percent of builders in a recent NAHB survey said they plan to construct smaller homes.

The decline in home size follows decades of sustained growth, culminating in the McMansions that blight many modern developments. Toward the end of his presentation, Ahluwalia mentioned the work of architect Sarah Susanka, whose 1998 book The Not So Big House is revered among rightsizers. (One of her show houses is shown.) "It's real and it's happening," Ahluwalia said in reference to Susanka's philosophy. For Susanka, the January 21 seminar was a validating and somewhat surreal moment. "It was a trip to sit there and hear all the things I've been saying for many years suddenly becoming what people say they want," she said afterward. Susanka credits larger forces with the home-size shift. "Between the current market place and all the issues related to energy efficiency, people are grasping that more for more's sake also means a lot higher utility bills," she said.—Daniel DiClerico

Essential information: Learn more about rightsizing in this interview with architect Marrianne Cusato.