Everyone likes the idea of first-time buyers, those fresh-faced couples setting up home with thoughts of family ahead. But heartwarming as it might be to see their numbers growing – the National Association of Realtors reported a third monthly rise in pending home sales on Tuesday, spurred by the first timers – it seems optimistic to assume that they can prop up the housing market alone. Meanwhile, policymakers subsidising new buyers should listen to the distinct creaking sound coming from the top end of the housing market.

According to Loan Performance, 8.8 per cent of jumbo mortgages are now more than 60 days overdue, almost twice the proportion of smaller prime mortgages. In 2007, a 10th of US mortgages were jumbos, accounting for 30 per cent of outstanding mortgages by value. (A jumbo mortgage is anything too big to be backed by the former government-sponsored enterprises Fannie Mae and Freddie Mac – typically $417,000, before being temporarily raised to $730,000 last year.) Until October 2007, such mortgages persistently recorded lower delinquency rates than prime home loans. But, whereas prime mortgage rates have headed downwards to record lows, 30-year jumbo rates have only moderated, to 6.5 per cent, above rates typical between 2002-06.