NY Times Advertisement As for housing prices, Mr. Rosenberg expects further declines of 10 to 15 percent over the next few years. He pointed to the roughly nine million residential housing units available for sale across the country, a very high vacancy rate when judged against a total housing stock of 130 million units. If his forecast is accurate, the numbers of borrowers who owe more than their homes are worth will rise significantly. Mr. Rosenberg estimates that fully half of the mortgage-holding population in the country could be underwater by 2011. For now, these borrowers are getting little to no help from lenders no surprise or from the government. Indeed, the Obama administrations loan modification program has more or less allowed banks that own second mortgages on troubled borrowers homes to continue to press for full repayment of these obligations.