Long-term mortgage interest rates were flat Friday, and the benchmark 10 year Treasury bond yield rose to 4.37%. The 30 year fixed-rate average held at 5.66%, and the 15 year fixed-rate stayed at 5.23%. The 1 year adjustable remained at 4.49%. The 30 year Treasury bond yield increased to 4.56%. Mortgage rate figures are according to Bankrate.com, which publishes nightly averages based on its survey of 4,000 banks in 50 states.