Home prices in the United States are the most affordable they have been in 18 years, according to the National Association of Home Builders and the Wells Fargo Housing Opportunity.

The NAHB said that affordable interest rates and low prices helped the affordability rates during the second quarter of 2009.

The report also 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 of 72.5 percent during the previous quarter and up from 55 percent during the second quarter of 2008.

“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.”

Robson noted that the tax credit, which expires on Nov. 30, is currently limited to just buyers purchasing their first home.

Indianapolis was once again determined to be the most affordable major housing market in the country during the second quarter. Almost 95 percent of all homes sold were affordable to households earning the area’s median family income of $68,100. Indianapolis has now topped the affordability list for 16 consecutive quarters.