The Ledbetter family likes to spend time at home together—just not always in the same room. So they built a 3,600-square-foot house with special rooms for studying and sewing, separate sitting areas for each child, and a master bedroom far from both. Then there's the escape room, where Mr. Ledbetter says, "Any family member can go to get away from the rest of us."

The Mercer Island, Washington, industrial designer says his 7- and 11-year-old daughters fight less, because their new house gives them so many ways to avoid each other. "It just doesn't make sense for us to do everything together all the time," he says.

After two decades of pushing the open floor plan—where domestic life revolved around a big central space and exposed kitchens gave everyone a view of half the house—major builders and top architects are walling people off. They're touting one-person Internet alcoves, locked-door away rooms, and his-and-her offices on opposite ends of the house. The new floor plans offer so much seclusion, they're "good for the dysfunctional family," says Gopal Ahluwahlia, director of research for the National Association of Home Builders.

The approach isn't for all architects. William Sherman, chairman of the department of architecture and landscape architecture at the University of Virginia, says all the cut-up spaces make families more isolated and lonelier than ever. "People don't even gather in the same spot to watch TV anymore," Mr. Sherman says. "It's sad."