The report by the Harvard University Joint Center for Housing Studies says nearly 1 million renter families were added to the mix in the past year -- four times the rate of new renters from 2003 to 2006, the MacArthur Foundation, which supported the study, reported.

"The demand for affordable rental housing is increasing at the same time that the supply of low-cost rental homes is declining," MacArthur President Jonathan Fanton said.

"The debate on national housing policy must not exclude the more than 35 million renter households," Fanton added.

The study found that conversion from rental property to condos was larger in 2005 than the number of new family homes completed.

Further, the report said, 2.2 million rental units were razed or taken out of the rental market between 1995 and 2005.

Rental fees and renters' incomes have also crossed paths.

The median gross rent for the country rose 2.7 percent from 2001 to 2006, while median renter incomes fell by 8.4 percent, the report said.