There are over 310 million people living in the country, forming approximately 113 million households. Roughly speaking, about 3 people live under the same roof, on average.
Every year about 2.5 to 3 million additional people are added as the number of births run at around 4 million per year, deaths at 2 million, and 1 million or so are added through immigration inflow. Normally, such population gains would translate into 1 million household formations each year, which would directly translate into 1 million in housing demand in the form of either renters or homeowners. But household formation came to a halt because of difficult economic circumstances, with more people doubling/tripling up and a greater number of young adults living with their parents.
Interestingly, the squashing of households has been principally in the number of homeowners. From the bursting of the housing bubble, homeowner households have not increased at all in the past six years. But the number of renters has steadily risen. Rents will rise as a result. Rising rents also mean added pressure to broader consumer price inflation since this rental component is one of the bigger weights in the inflation calculation (more so than even gasoline or food prices).