The nation’s love affair with McMansions continues to wane: The average size of new single-family homes completed last year fell again, a trend expected to continue for several years, the National Association of Home Builders said at its annual conference recently.

In 2010, completed homes measured an average 2,377 square feet, down about 3% from the year earlier. By 2015, many builders expect the average home size to shrink to 2,152 square feet.

This downsizing ends an expansion that spanned nearly three decades: The average size peaked at 2,521 square feet back in 2007.

More than half of builders expect to build smaller and lower-priced models in 2011, a move that lets them compete with foreclosures and appeal to buyers who can no longer afford—or who no longer want—the boom-era’s supersized showpieces.

Last year, the number of homes with three or more bathrooms came in at 24%, flat from the previous year, but down from 28% in 2008. Homes with garages for three or more cars declined to 17% of homes from 20% in 2005.

Down the road, many builders expect the family room area to increase, while little-used areas like the  living room, entry foyer and dining room will likely take up less space. By 2015, great rooms—more flexibile living space—could be the norm, the NAHB survey found.

Another expected change? Master bedrooms will be moved to the first floor, allowing older owners to avoid the stairs as they age in place. The kitchen of tomorrow, meanwhile, will probably include a double sink, recessed lighting and table space for eating.

To be sure, not everyone agrees that the age of oversized homes is officially over. The NAHB noted that the average size of homes started last year rose slightly in the South. And an online survey by Better Homes and Gardens magazine found that about 40% of consumers want to increase their total home size with their next move. The median square footage of current homes is 1,864 homes, slightly below the desired 1,914 square feet.