(AP) – Average U.S. rates on fixed mortgages changed little this week and remained slightly above record lows reached earlier this year. The low rates have aided a modest housing recovery.

Mortgage buyer Freddie Mac said Thursday the rate on the 30-year loan slipped to 3.55%, down from 3.59% last week. Six weeks ago, the rate fell to 3.49%, the lowest since long-term mortgages began in the 1950s.

The average on the 15-year fixed mortgage, a popular refinancing option, was unchanged at 2.86%. That’s above the record low of 2.80% reached six weeks ago.

Cheap mortgages have lifted home sales this year. Sales of newly built and previously occupied homes are well above last year’s levels. Prices have increased consistently, largely because the supply of homes has shrunk while sales have risen. And builder confidence is at its highest level in five years.

Still, the housing market has a long way back to full health. Some economists forecast that sales of previously occupied homes will rise 8% this year to about 4.6 million. That’s well below the 5.5 million annual sales considered healthy. Many people are still having difficulty qualifying for home loans or can’t afford larger down payments required by banks.

Mortgage rates are low because they tend to track the yield on the 10-year Treasury note. A weaker U.S. economy and uncertainty about how Europe will resolve its debt crisis have led investors to buy more Treasury securities, which are considered safe investments. As demand for Treasurys increase, the yield falls.

To calculate average rates, Freddie Mac surveys lenders across the country on Monday through Wednesday of each week.

The average does not include extra fees, known as points, which most borrowers must pay to get the lowest rates. One point equals 1% of the loan amount.

The average fee for 30-year loans was 0.7 point, up from 0.6 point last week. The fee for 15-year loans was unchanged at 0.6 points.

The average rate on one-year adjustable rate mortgages declined to 2.61% from 2.63% last week. The fee for one-year adjustable rate loans was steady at 0.4 points.

The average rate on five-year adjustable rate mortgages fell to 2.75% from 2.78%. The fee edged up to 0.7 points from 0.6.