The commercial sector continues to lead the American Institute of Architects' billings index, which has remained in positive territory for the fifth consecutive month, the group reported Thursday.

The index reflects a nine-to-12-month lag between architecture billings and construction spending. "We are starting to hear more about improving conditions in the marketplace, with a greater sense of optimism that there will be greater demand for design services," said the group's chief economist Kermit Baker. A number of firms continue to struggle, however, "so progress is likely to be measured in inches rather than miles for the next few months."

— Alan J. Heavens