by CalculatedRisk on 5/28/2008 11:50:00 PM

Housing Wire has more on the S&P Alt-A downgrades: S&P Lowers the Boom on 1,326 Alt-A RMBS Classes

The downgrades affect an $33.95 billion in issuance value and affect Alt-A loan pools securitized in the first half of 2007 — roughly 14 percent of S&P’s entire Alt-A universe in that timeframe.

Perhaps more telling were an additional 567 other Alt-A classes put on negative credit watch by the ratings agency.

A review of affected securities by Housing Wire found that all of the classes put on watch for a pending downgrade are currently rated AAA, suggesting that S&P’s confidence in thin overcollateralization typical of most Alt-A deals is quickly waning. The total dollar of potential downgrades to the AAA classes in question would dwarf Wednesday’s downgrades, which affected only mezzanine and equity tranches.