by Calculated Risk on 6/20/2012 04:25:00 PM

From the Census Bureau: Sharing a Household: Household Composition and Economic Well-Being: 2007–2010

In spring 2007, there were 19.7 million shared households. By spring 2010, the number of shared households had increased by 11.4 percent, while all households increased by only 1.3 percent

According to the report, there were 22.0 million shared households in spring 2010.

Most of the adults sharing a household were related:

In both 2007 and 2010, additional adults were more likely to live with relatives than with nonrelatives. In 2010, additional adults related to the householder accounted for 81.8 percent of all additional adults. ... additional adults related to the householder rose by 2.4 million ... Additional adults not related to the householder, i.e., roomates, housemates, or boarders, increased by 910,000 between 2007 and 2010.

About 1.2 million were adult children of the householder (823 thousand were in the 25 to 34 age bracket). These are the people that we discussed as "moving into their parent's basement". Other relatives moving in included parents, siblings, adult grandchildren (190 thousand), and others.

Definition from Census:

This report classifies a shared household as a household which includes at least one “additional adult,” a person aged 18 or older who is not enrolled in school and who is neither the householder, the spouse, nor the cohabiting partner of the householder.

A large number of these adults will eventually move out of their parent's (grandparent's) homes. The recent surge in rental demand suggests that many of these people are already moving out. This will be demand for housing units, although mostly for rental units.