Who's moving in? Adult kids, aging parents

• Many homeowners expect grown children or aging parents to move in
• Family size has gone up more than 3% since 2000, largely due to economy
• Growing household trend an 'enormous change,' housing industry expert says

Almost a third of homeowners expect their grown children or aging parents to eventually move in with them, according to a survey by one of the nation's largest home builders.

About one in seven say they already have a "boomerang kid" — an adult child who moves back home — or elderly parent living under their roof.

The survey out Wednesday of more than 1,000 homeowners by PulteGroup, builder of everything from starter homes to upscale residences and Del Webb adult communities, shows that the rise in multi-generational households may continue.

"It's an enormous change," says Stephen Melman, director of economic services at the National Association of Home Builders. "I remember when I was in college, no one wanted to be near their parents."

A Pew Research report earlier this year showed that the share of Americans living in multi-generational households is at its highest since the 1950s. Young adults ages 25 to 34 are most likely to return to the nest. Almost 22% of young adults were living at home in 2010, up from 16% in 2000 and rising the most since the recession that began in 2007 and technically ended in 2009.

Average family size has gone up more than 3% since 2000, largely a result of tough economic times. The rise in immigrants from countries accustomed to several generations living together also pushed the number.

These demographic shifts are altering the needs of home buyers and prompting home builders to create new floor plans. We're looking at housing now for usable space," says Deborah Wahl Meyer, PulteGroup's chief marketing officer. "How do we make it practical?"

Pulte's online survey shows that finances often drive these household arrangements. It also found many households where parents moved back in to strengthen family bonds.

Pulte is testing different features to appeal to the "new" American family of Mom, Dad, adult child and older parent and sometimes grandchildren.

Out: Showy and dramatic living rooms and fancy dining rooms that are rarely used, Meyer says. In:

More than one master suite to accommodate adult relatives — often one upstairs and one downstairs.

An open family-office space off the kitchen where the kids do homework or parents pay bills online.

Connie Kirby and husband Evon, a retired New York City detective, bought a Pulte home in Mesa, Ariz., a year ago. They live with their three children (ages 16, 14, 11), his father and a nephew, 21, in a six-bedroom, 4,400-square-foot home.

"It was easier and more economical to move in together," says Connie, 44, a travel agent. "Our neighbor has three generations in their house." She expects her kids to stay when they're adults or leave and come back.