In interviews, couples and sociologists say that often it has nothing to do with sex. More likely, it has to do with snoring. Or with children crying. Or with getting up and heading for the gym at 5:30 in the morning. Or with sending e-mail messages until well after midnight.
In a survey in February by the National Association of Home Builders, builders and architects predicted that more than 60 percent of custom houses would have dual master bedrooms by 2015, according to Gopal Ahluwalia, staff vice president of research at the builders association. Some builders say more than a quarter of their new projects already do.