The percentage of houses that are affordable for U.S. median income families dropped to a 10-year low in the third quarter, the National Association of Home Builders (NAHB) said on Thursday.

According to NAHB, 56.4 percent of new and existing homes sold in the third quarter were affordable to U.S. families earning the median income of 71,900 U.S. dollars.

The percentage was the lowest reading since mid-2008, while it was also 0.7 percentage point lower than the figure in the second quarter, NAHB said.

The median home price in the United States edged up by 3,000 U.S. dollars to 268,000 U.S. dollars in the third quarter. This is also the highest quarterly median price in the history according to NAHB's data series.

Meanwhile, average mortgage rates in the United States rose by a nominal 5 basis points in the third quarter to 4.72 percent, said NAHB.

"Continuing home price appreciation and rising interest rates coupled with persistent labor shortages are contributing to housing affordability concerns," said NAHB Chairman Randy Noel.

"Builders are increasingly focusing on managing home construction costs so that they do not outpace wage gains," said Noel.

Although housing affordability had dropped recently, Robert Dietz, Chief Economist of NAHB, noted that ongoing job and economic growth in the United States will provide "a solid backdrop" for housing demand.

"However, housing affordability will need to stabilize to keep forward momentum from diminishing as we move into the new year," Dietz added.