According to the National Association of Home Builders/Wells Fargo Housing Opportunity Index, housing affordability remains near its highest level in 18 years.

"The increase in affordability, along with the $8,000 federal tax credit for home buyers, is stimulating demand, particularly among young, first-time buyers," said NAHB Chairman Joe Robson, a home builder from Tulsa, Okla. "But to keep the recent upturn in home sales going into next year, Congress will need to extend the tax credit for another year and make it available to all buyers in an effort to encourage activity in the trade-up market."

The HOI showed that 72.3 percent of all new and existing homes sold in the second quarter of 2009 were affordable to families earning the national median income of $64,000, down only slightly from the record-high 72.5 percent during the previous quarter and up from 55.0 percent during the second quarter of 2008.