American architecture firms’ billings, a leading indicator for the construction industry, had their biggest gain in more than seven years last month, according to a survey by the American Institute of Architects.

Billings generated a score of 60.5 on the institute’s Architecture Billings Index in September, up from 55.9 in August. A score above 50 indicates an increase in billings, the Washington-based group said on Tuesday in a statement. It was the largest monthly gain since mid-1998, a spokesman, Scott Frank, said.

Commercial building construction, which accounts for about 8% of gross domestic product, typically follows billings for architectural services by about six months, the institute said. The construction of office buildings, shopping malls, apartment complexes, and other commercial buildings should pick up next year, driven by low interest rates and “moderate overall inflation,” the group said.

The survey’s results “should be encouraging for the nonresidential construction industry, and those business sectors affected by it,” the institute’s chief economist, Kermit Baker, said in the statement. “The positive outlook should be tempered, however, because of the effect that rising energy prices, increased costs for building materials, and the possibility of rising interest rates will have on the overall economy in the months to come.”

The American Institute of Architects has conducted the monthly survey of firms owned by its members since 1995. The results of the survey had previously been shared only with institute members and academics.

Starting this month, the institute is releasing the results to the public, Mr. Frank said. The change in policy coincides with the publication of a paper on using billings at architecture firms as an indicator for construction in the journal Business Economics. The paper, co-written by Mr. Baker, will be published in the journal’s October issue, Mr. Frank said.