"You're coming home?"

That's often the surprised reaction of homeowners who think they're in the clear after their children go off to college. They assume their kids will take their degrees, get a job and move into their own place.So just as these wishful thinkers start looking forward to their "empty-nester" phases of life, many run head-on into the "boomerang" effect: In an economy coming out of a deep recession the children - and their grandparents - find themselves moving back in.

"When the economy started getting thick, you started seeing more of . . . that scenario," says Steve Moore, architect with the Des Moines-based Bloodgood, Sharp Buster, a national design firm.

Perhaps as a result of that trend, and in addition to current relatively low interest rates on mortgages, buyers over the age of 45 are purchasing bigger homes, according to statistics from the National Association for Homebuilders in Washington.

Although the average family size has declined since the 1960s from 3.6 people per home to 2.27 people, home sizes have increased from an average 1,400 square feet to 2,100 square feet, says Gopal Ahlu-walia, NAHB economist.

The trend will continue in the future, with further decline in family size and expansion in square footage, he says.

The pattern is driven in some degree by parents who are no longer burdened with college tuition bills and earning more money as they reach the peaks of the careers, says Jay Shackford, NAHB spokesman. They want to use the extra cash to buy a more spacious home, he says.

At that point, parents will set aside an area that can serve a variety of functions at different times, says Moore.

The "swing suite" concept in a two-story home includes a room and attached full bath on the first floor with the master bed and bath on the second floor.

"Typically it's for those scenarios where you've got an elderly person, so you don't have to worry about second-floor access," says Moore.

Yet the accommodations would also suit the college grad, guests or a separate study, depending on the particular need.

"(The design) is becoming very popular because it does allow somebody to be out from under your feet," says Barry Berkus, president of the international Berkus Design Studio based in Santa Barbara, Calif.

The concept originated in Japanese architecture, which developers have mass-marketed since the 1980s. Following the traditional family structure where several generations often live under one roof, each story of a house serves a different age group from the children to the grand-parents and in-laws, said Berkus.

He says his company has been designing similar homes in the United States for 20 years.

"We looked at it hard as people started to double up in the work force and people started coming home," he says. "As soon as you realize that this part of the makeup of the family, then you have to start designing for it."

Depending on which area of the country the home is in, national architects say, the design can take on any variety of forms.

It could be contained in a detached guest house in California or in desert areas where the normally clear weather allows for easy outdoor travel between the two spaces. In the less weather-friendly Midwest or Northeast, says Berkus, the suite could be in the basement or on the first floor of a house.

Florida developers have adopted different forms in the state where residents are used to having regular visitors to its sunny climate.

Because most homes are one story in Florida, it's a matter of stretching them out to add an extra grouping of rooms, says Larry Sietsman, president of the Melbourne-based Holiday Builders.

"You can take a four-bedroom home, make it three bedroom and add a bath," he says, "or you can stretch a home to add another kitchen or bath."

The "courtyard" design is popular in affluent Florida communities, says Moore, because the main house may be centered around a central pool area, while an extra wing stretches out to the street and can serve as a living area, den or garage.

The emphasis anywhere, designers say, is always on the versatility with which the space can be used.

"You've got a lot of different needs that that particular room can handle at different times," said Moore.