When it is completed in the autumn of next year, the two-tower structure will become US luxury homebuilder Toll Brothers’ 27th finished property in the New York City area. It is being financed in part by debt lapped up by yield-starved investors amid a global rally for bonds — which has driven Toll Brothers’ cost of borrowing to its lowest level for more than a decade. Last week the Horsham, Pennsylvania-based company sold a $400m 10-year bond with a coupon of just 3.8 per cent, joining a tiny club of companies that have managed to sell what are traditionally called high-yield bonds, also known as “junk” bonds, below 4 per cent.