Many Americans are building bulwarks against poverty out of roommates, group houses and their parents' spare rooms, with a Census report released on Wednesday finding the number of people considered "additional adults" in U.S. households grew between 2007 and 2011.

In 2011, 17.9 percent of those 18 or older were considered "additional adults," compared to 2007, when 16 percent of legal adults fell within the definition.

An additional adult is someone who is not the head of a household, and is living with someone other than a spouse or domestic partner. The Census also does not count college students.