Is owning a home becoming more difficult?

Home prices in the United States are staying relatively affordable following the burst of the late-2000s real estate bubble, but a growing number of US counties are seeing their housing markets become pricier than they have historically been.

RealtyTrac, an online real estate sales forum and data center, released its Home Affordability Index for the first quarter of 2016 on Thursday. The report took data from 456 counties around the US, analyzing the relationship between average wages and monthly housing payments to calculate an estimate for regional home affordability.

Most of the counties evaluated by RealtyTrac were in line with their historic standards of affordability, but the information company found around 9 percent of US county housing markets were made up of homes that cost more than average wages could provide for. That number is far down from the 99 percent experienced in mid-2006, but is up from last year’s 2 percent.

“While the vast majority of housing markets are still affordable by their own historic standards, home prices are floating out of reach for average wage earners in a growing number of US housing markets,” RealtyTrac vice president Daren Blomquist wrote in the report.

RealtyTrac used average wage data from the US Bureau of Labor Statistics as a marker for what workers earn on a county-by-county basis, and compared that information with a typical monthly housing payment. That amount was calculated based on an average 30-year fixed-rate mortgage on a median-priced home, using interest rates from a Freddie Mac mortgage survey.

Using historic affordability based on monthly payments works well as a gauge on the market, but the recent drop in interest rates has counteracted some markets’ home appreciation, meaning that “the affordability equation could change quickly if interest rates trend higher and home prices continue to rise faster than wages,” Blomquist wrote.

Additionally, the counties analyzed by RealtyTrac are all populated by 100,000 people or more, meaning the report's results could be less applicable in rural regions than more heavily urban ones. And home appreciation and the prevailing higher costs of living in cities could make the affordability gap appear even larger in metropolitan areas.

Of the 43 counties found to be historically less affordable in this study, the five most populous were in metro areas near or including Dallas, Detroit, San Francisco, and New York City. The five most populous counties listed as more affordable than their historic norms by RealtyTrac were in the Los Angeles, San Diego, Chicago, Houston, and Phoenix metro areas.

Despite finding that less than one-tenth of US housing markets are below their historic affordability levels, RealtyTrac did calculate that nearly two-thirds of the markets are experiencing an annual rise in home prices that outpaces their rise in wages. With only 39 percent of counties showing wage growth outpacing home price increases this year, many regions could see a shift in their housing affordability in the coming years, including some centered around the Los Angeles, New York, Phoenix, Dallas, Las Vegas, and Seattle metro areas.

“I’m sure it comes as no surprise to anyone in Seattle that it’s getting harder and harder to afford a home,” said Matthew Gardner, chief economist of Seattle-based Windermere Real Estate. “Thanks in part to strong income growth and intense competition, home prices continue to escalate at rates that are negatively impacting affordability.”