Average interest rates on U.S. 30-year mortgages dropped for the fourth week in a row, to 6.52 percent, according to a survey released by mortgage finance company Freddie Mac Thursday.

Rates on U.S. 30-year mortgages were 6.55 percent last week. Average rates on 15-year mortgages remained unchanged at 6.20 percent.

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One-year adjustable rate mortgages dropped as well, to 5.65 percent from 5.69 percent.

"Long-term rates continue to relax as economic reports support a picture of a weakening housing sector and a slower-growing economy," said Frank Nothaft, chief economist of Freddie Mac (FRE), in a statement.

On Wednesday, the Commerce Department reported that construction on new houses slowed to the lowest rate in two years in July, to 1.795 million homes. Applications for building permits in July fell by 6.5 percent, the biggest decline since a 7.2 percent drop in September 1999.

Lenders charged an average of 0.3 percent in fees and points on 30-year and 15-year mortgages, both unchanged from last week. They charged 0.5 percent in fees and points on the one-year ARM, down from 0.8 percent last week.

The hybrid "5/1" ARM, set at a fixed rate for five years and adjustable each following year, averaged 6.18 percent, down from 6.21 percent last week.

Freddie Mac is a mortgage finance company chartered by Congress that buys mortgages from lenders and packages them into securities to sell to investors or to hold in its own portfolio.

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