From 2008 to 2011, renters’ housing costs increased almost 6%, while their income fell 3.2% according to the Center for Housing Policy. More than 26% of working renters spent at least half their income on housing in 2011, up from about 23% in 2008, writes Bloomberg Businessweek.

One reason: There just aren’t enough affordable rental units to go around. In 2010, there were 5.1 million more low-income families than there were affordable units.