Substantially enhanced ratings stability and greater overall credit support are expected in U.S. residential-mortgage-backed securities deals rated by Standard & Poor's Ratings Services due to revised overcollateralization floor guidelines that resulted from altered modeling assumptions on provisions that allow the release of credit support after the step-down date in the transactions. Five classes of certificates issued by NovaStar Mortgage Funding Trust in 2004 have been placed on review for possible downgrades by Moody's Investors Service, the agency announced. S&P reportedly downgraded 1713 classes of subprime, Alt-A and second mortgage transactions issued this year for $23.35 billion.
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