These so-called underwater mortgages pose a roadblock to a housing recovery because the properties are more likely to fall into bank foreclosure and get dumped into an already saturated market. Economists from J.P. Morgan Chase & Co. said Monday they didn’t expect U.S. home prices to hit bottom until early 2011, citing the prospect of oversupply.

Home prices have fallen so far that 5.3 million U.S. households are tied to mortgages that are at least 20% higher than their home’s value, the First American report said. More than 520,000 of these borrowers have received a notice of default, according to First American.