Despite neighborhoods littered with vacant homes and sale prices that dropped dramatically in the past three years, more Americans are spending more of their money on housing expenses than ever before. A report by Harvard University's Joint Center for Housing Studies found 18.6 million American households –renters and homeowners alike – spend more than half their income on housing, up from 13.8 million in 2001. Dedicating more than 30 percent of income to rent or mortgage is considered unhealthy.

The study, Harvard's annual State of the Nation's Housing report found that as the housing market slowly recovers, it is getting harder for low-income people to afford their homes. More homeowners and renters are devoting half or more of their income to housing costs than ever before. And low-income renters are the most burdened.

It wasn't always so dire. In 1960, only 12 percent of renters spent half their income on housing. Between 2000 and 2008, that number jumped by a third, to 16 percent. And among the poorest 20 percent of renters, half now spend 54 percent of their income on housing. The report's authors blame falling wages.

“After at least three decades of progress, real median household incomes will almost certainly end the 2000s lower than they started. At last measure, the median for all households was $49,800 in 2008, down from $52,400 in 2000,” according to the report.

Many families earning as much as three times the minimum wage devote half their income to housing, the study reports.

“This stems from a mismatch between their low incomes and the cost to supply the most basic of homes. The median income of households in the bottom quartile was $14,868 in 2008. At that level, their monthly housing costs (including utilities) would have to be no more than $372 to meet the 30-percent-of-income affordability standard. But finding even modest housing at such a low cost is next to impossible. Nowhere in the country is the HUD fair market rent for even a one-bedroom apartment at or below $372,” the report states.

And most of the people eligible for government housing subsidies aren't getting them.

“Despite federal support for rental assistance of about $45 billion per year, only about one-quarter of eligible renter households report receiving housing assistance,” according to the report.

As the federal government struggles with record budget gaps and the U.S. Department of Housing and Urban Development begins to rewrite its rental assistance programs housing subsidies are likely to suffer, the study suggests. “Efforts to impose fiscal austerity may take a toll on programs to cope with these challenges,” the study states.