Architecture firm billings growth softened in December but remained positive for the 15th consecutive month, according to the American Institute of Architects. A billings index for December registered 50.4, down from 54.7 in November. Any reading above 50 indicates an increase in billings. Billings remained strong in the Midwest. “The month of December has shown the Midwest a 3.2 point increase from November to December, which is great. Construction in the Midwest seems unaffected by the ongoing tariff situation thus far compared to the soft growth in other areas across the United States. This is similar to what we saw in the mid-2000’s, when market growth declined on the coasts but here in Iowa we stayed fairly insulated compared to the rest of the market,” Jessica Reinert, executive director of AIA Iowa, said in a release. “We hope the growing concern of unstable business conditions and the federal government shutdown won’t affect the design professions in the coming months but it certainly could have an impact.” Design firms in the Midwest scored 56.3 in December, while firms in the Northeast registered 51.6, in the South, 49.4 and in the West 49.2.