Last month's slowdown, following an upward turn in December, could be attributed to the winter weather, according to AIA chief economist Kermit Baker.

The index fell to 49.9 in January from 52.6 in December.  A reading above 50 indicates an increase in billings. The index, based on a survey of U.S. architects, reflects the roughly nine to 12 months between architecture billings and construction spending. “This easing in demand for design services is…