It's no surprise that renters in America's largest cities are facing a rental affordability crisis. In 2015, renters are expected to pay nearly 30 percent of their income toward the median national rent.

The research team at Zillow looked at housing data in cities in the West and grouped households based on their rent burden (the share of monthly household income dedicated to rent payments), separating them into high, medium and low rent-burden households.

Increasing rents, slow income growth and a shortage of low-income housing are impacting affordability, but which renter demographic groups are affected the most?

Their findings identify the households that are confronted with the highest rent burdens, and give some more context to America's rent affordability problem.

Households with the highest rent burden spend over half their income on rent

The general rule of thumb is to budget 30 percent or less of your household income on housing. But in households with the greatest rent burdens, that percentage is much higher. In Los Angeles, the highest rent-burdened households contributed 68 cents of every dollar earned to rent. Comparatively, the least rent-burdened households spent 14 to 15 cents of each dollar earned on rent.

Overly burdened renters tend to be older

In households with the highest rent burdens, the median age was three to five years older than those with low rent burdens. However, having older household members doesn't translate to more working-age or full-time employed adults.

High rent burden households are more likely to have children

These households are also twice as likely to be single-parent homes. 20 to 50 percent of low-income households have children present.

Difference in rent burden is largely due to difference in income

Low-income renters pay slightly less in rent, but not significantly. Most of the difference between low and high rent-burdened households can be attributed to income disparities. The median income of a low rent burden household is typically four to five times more than a high rent burden household.

Head over to the Zillow Research blog to read about more of the key findings.

Source: Analysis based on Zillow tabulations of data from the U.S. Census Bureau's American Community Survey, 2011-2013, made available by the University of Minnesota, IPUMS-USA. San Jose corresponds to Santa Clara County. Incomes and rents are updated using appropriate changes in the Consumer Price Index.

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