According to new U.S. housing market research by Zillow, the combination of rising home prices and interest rates creates a doubly challenging environment for would-be home buyers, making monthly mortgage payments on even modestly priced homes more of a financial burden.

A monthly mortgage payment for the typical U.S. home requires 17.5 percent of the median income, up from 15.4 percent a year earlier, according to Zillow's second quarter affordability report.

Between 2012 and 2016, mortgage rates hovered near historic lows, extending what buyers could afford even as home values recovered from the Great Recession and reached new heights. But interest rates have shown a marked increase in 2017 and 2018, eating into that affordability. The monthly mortgage burden is greater than the historic average in 10 of the 50 biggest U.S. housing markets. Seven of these 10 markets are along the West Coast, which has seen particularly strong home value appreciation since the recession.

The typical rent now requires 28.4 percent of the median income, slightly lower than it did a year ago as rent growth has slowed below the pace of income growth. Although rent affordability remains worse today than it was in the 1980s and 1990s, it has gradually improved after peaking in late 2010.