This article was originally featured on our sister site ARCHITECT.

The monthly Architecture Billings Index (ABI) came in at a score of 53.0 in May, up 2.1 points from April's 50.9, the AIA announced today.

The ABI is a leading economic indicator of construction activity in the U.S., and reflects a nine- to 12-month lead time between architecture billings and construction spending nationally, and regionally, as well as by project type. A score above 50, as seen in May, represents an increase in billings from the previous month, while a score below 50 represents a contraction.

May's positive reading marks the fourth consecutive month of growth in design services since January's marginal decline. The new project inquiries index—the most reliable indicator of future billings—increased in April, making May's 2.1 gain unsurprising. Continued gains in June can be expected, as the new project inquiries index increased to 62.4 in May, up 2.2 points from April's already healthy score of 60.2.

“The fact that the data surrounding both new project inquiries and design contracts have remained positive every month this year, while reaching their highest scores for the year, is a good indication that both the architecture and construction sectors will remain healthy for the foreseeable future,” said AIA chief economist Kermit Baker, Hon. AIA, in a press release. “This growth hasn’t been an overnight escalation, but rather a steady, stable increase.”

The design contracts portion of the index increased 1.6 points in May, from April's score of 53.2, to a score of 54.8. Both inquiries and design contracts have stayed above the 50-point threshold every month in 2017, a sign that momentum is strong in the market despite fluctuations in pace month to month.

Regional billings, which, unlike the national score, are calculated as a three-month moving average, decreased in two of four regions in May. The Northeast was the only region to fall below the 50-point growth threshold, with a score of 46.5. May is the second month that design services have declined in the Northeast, with this month's reading marking further decline from April's score of 49.5. Billings in the Midwest also posted a decline in May, but stayed above 50 with a score of 50.4, indicating design services increased, albeit at a slower pace than seen in April. Design services maintained their pace in the West, with a positive score of 52.3; the same score posted a month prior. The South was the only region to see an increase in billings month-over-month with a score of 56.1, a 0.8 point gain from April's reading of 55.3.

All four sectors posted scores above 50 in May, indicating an increase in design services. The mixed practice sector was the only sector to see an increase in pace however, with a 0.7-point gain from April's score of 55.1, to a score of 55.8. May marks the third consecutive month that mixed practice has posted the strongest score of any other sector, with the institutional sector leading during the first two months of 2017. (Results of sectors are also calculated as a three-month moving average.)