The rise in multigenerational housing means builders will have to serve multiple interests under one roof.

For Bill Elliott, chief operating officer for custom homebuilder Blackstowne Development LLC in Charlotte, N.C., the gloomy economy dried up much of the market for larger homes priced above $400,000. That is, except for one niche customer: Those in need of room for the kids, parents, and grandparents.

In-law suites are popular, he says. And that's in addition to kids moving back into Baby Boomers' homes, he adds.

According to a Pew Research Center study, the phenomenon of multigenerational households (homes shared by at least three generations from the same family) has picked up steam of late as the recession has forced people to pool resources, young people are marrying later, and more family-centric immigrants are entering the country.

Between 2000 and 2008, the number of Americans living in these households grew by 7 million people, to total 49 million, according to the study.

In his book Casa Y Comunidad: Latino Home and Neighborhood Design, former HUD Secretary Henry Cisneros writes that Hispanics, who often live in multigenerational homes, want more and smaller bedrooms, garages that can be converted to livable space, ample parking, and easy access between living areas and the outside.

Elliott says his company is building multigenerational homes for "Sandwich Generation" Baby Boomers caring for both their kids and parents. Sought-after features include two master suites, a second cooking area, a larger septic system, and more closets.

"If you are going to put another family in the basement, you may want to put in a second master bath or a kitchenette," he says.