The commercial mortgage default rate on loans held by US banks more than doubled to 3.4% in the third quarter as vacancies rose and rents declined, Real Estate Econometrics said.

Defaults climbed from 1.37% a year earlier and from 2.88% in the second quarter, the New York-based property research firm said today in a report. Default rates in the first three quarters of 2009 have been the highest since 1993, the firm said.