The housing bust left thousands of empty, unfinished or foreclosed homes laying empty across the U.S. That means that there should be plenty of affordable housing, right? Wrong--not for renters anyway.

Over the past few decades, rental affordability has become a widespread problem in the U.S. as rent levels grew faster than renter income. Nearly half of renters pay more than 30 percent of their monthly income for rent, including 26 percent that pay more than 50 percent of income, according to a new report by Harvard University's Joint Center for Housing Studies. For this report we identified and ranked the nation's top 10 metropolitan areas by the percentage of tenants spending more than half of their income on rent.

And it’s not necessarily the most expensive cities that are to blame. While renters in such high-cost cities as New York and San Francisco grumble about how much they pay their landlords every month, residents in the Miami, McAllen, Tex., and Detroit metro areas are actually more strained, according to the Harvard report.

In fact, metro Miami has the greatest share of residents who pay more than half of their income to rent in the nation. The share reached 34.2 percent in 2009, up from 26 percent in 2000, as real household income growth stagnated and median rent in the area, adjusted for inflation, rose by 22.2 percent during that period, according to the Harvard report. In McAllen, the share of severely burdened renters rose to 33.1 percent and in Detroit to 32.8 percent.

The amount of income apportioned to rent has grown dramatically over the past fifty years. In 1960, about one-quarter of renters in the U.S. were at least moderately burdened, including 12 percent with a severe burden, according to Harvard's Joint Center. By 2009, the rate doubled to nearly half of renters with at least a moderate burden, including 26 percent with a severe burden.

“The impact is on what decisions families have to make. They will spend less on things that are important to their well being, such as healthcare, food, and savings,” says Chris Herbert, research director at the Joint Center. “There are also tradeoffs on the types of places they occupy and where they live, which also affects other life outcomes” and access to jobs, schools and other opportunities, he adds.

As more Americans are expected to rent in the next few years until restrictions on homeownership ease, increases in rent levels are expected to continue outpacing income growth. Demand for rentals also may continue to grow as the preference for homeownership changes. Unfortunately for cost-burdened renters, Matthew Greer, chief executive of Carlisle Development Group, Florida’s biggest developer of affordable housing with about 4,000 affordable rental units in the Miami metro area—says, as this happens, "the supply of affordable housing near the job core or by rapid transit lines is going to be unbelievably insufficient."

Here are the 10 toughest U.S. cities for renters: