The number of families living in a household with another family rose by 70% between 2001 and 2011.
"Concealed families", as they are known, increased from 170,000 to 289,000 in that decade, according to figures from the Office of National Statistics - ten times the rate of unconcealed families.
Concealed families include couples, parents or single parents that live in the household of another family - the "primary family".
The two families are often from the same extended family: for example, two parents, their daughter and her husband all living in the same house.
The ONS says the statistics are a useful indicator of housing demand for house building and planning in the future.