Homes may be becoming less affordable due to higher prices, rising interest rates and stagnant incomes.

Rising prices put a big dent in housing affordability in the second quarter, according to the National Association of Home Builders (NAHB)/Wells Fargo Housing Opportunity Index.

Specifically, 69.3 percent of new and existing homes sold between the beginning of April and end of June were affordable to families earning the median income of $64,400. That's down from the 73.7 percent and the first time affordability has fallen below 70 percent since late 2008.

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"Housing affordability has been hovering near historic highs for the past several years, largely due to exceptionally favorable mortgage rates and low prices during the recession," said NAHB Chairman Rick Judson, a homebuilder from Charlotte, N.C.

But that scenario is ending as housing markets recover and home values strengthen. In addition, Judson said, the cost of building homes is rising due to tightening supplies of building materials, developable lots and labor.

The median price of all new and existing U.S. homes sold in the second quarter was $202,000, well above the second quarter 2012 median price of $185,000, noted NAHB Chief Economist David Crowe.

Ogden-Clearfield, Utah, was rated the nation's most affordable major housing market for a fourth consecutive quarter, and the Utica-Rome area in New York was named most affordable smaller market for the first time.

The San Francisco-San Mateo-Redwood City area in California was the least affordable area of all large markets. Just 19.3 percent of homes sold in the second quarter there were affordable to families earning the area’s median income of $101,200.

Richard Green, director of the University of Southern California's Lusk Center for Real Estate, told the Los Angeles Times that wage stagnation is the real reason behind declining affordability, noting that wages began to stagnate in the 1970s and have not kept pace with rising home prices.

"People are not making more money, except at the high end. This gets at the broader problem, which is not a housing problem. ... It seems to me the problem is much more of an income one."

Home prices will probably continue to rise in California, although rising rates will keep them from increasing quickly, California Association of Realtors Chief Economist Leslie Appleton-Young told the Times.

"It is going to continue to deteriorate, but perhaps at a lower rate. I do think you are going to see a cooling off of price appreciation."

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