The Census Bureau now offers solid proof for all those anecdotes about young adults moving back into their parents' homes and older people living longer, active lives. The agency recently highlighted this "doubling up" trend by reporting a 10.7% rise since 2007in multigenerational households–homes with three or more generations under one roof–and a 25.5% jump in the number of 25- to 34-year-olds living with their parents.

This is bad news for builders because it means reduced demand to build separate residences. It's also a trend that's likely to continue even after the economy recovers. "For millions of Americans, keeping generations of the family together under a single roof is a great solution," writes Custom Home, a sister publication of ProSales. "Grandparents are around to help watch little ones, and grown children save money by living in their parents' basement or attic."

Much of the increase is driven by larger Hispanic and Asian populations, whose cultures often revolve around a tight-knit family environment. And many of the multigenerational homes were found in suburbs and the outskirts of cities, where the families lived in single-family houses covering all ends of the economic spectrum.