After a significant improvement in March, architecture billings stumbled in April, according to the recently released monthly Architecture Billing Index (ABI).

The American Institute of Architects compiles the ABI, which indicates the level of demand for design services. An index reading above 50 reflects an increase in architecture billings; a reading below 50 reveals a decline in demand for architects’ and by extension, the level of spending on commercial construction in the months to come. This includes multifamily work, which scored a 43.2 in the April ABI, up 3.8 points. (Single-family activity is not covered in this particular index.)

That sector performed better than the overall ABI, which slipped to an overall reading of 42.8 in April, a reduction of 0.9 points compared to the previous month. Inquiries for new work held steady at a score of 56.8. “The most encouraging part of this news is that this is the second month with very strong inquiries for new projects. A growing number of architecture firms report potential projects arising from federal stimulus funds,” Kermit Baker, AIA’s chief economist, said in a statement. “Still, too many architects are continuing to report difficult conditions to feel confident that the economic landscape for the construction industry will improve very quickly. What these figures mean is that we could be seeing things turn around over a period of several months.”

Given the scope and time frame of many commercial projects, the ABI essentially offers a forecast for such construction activity at a time nine to 12 months in the future, which is a typical lag between architecture billings and construction spending.

Alison Rice is senior editor, online, at BUILDER magazine.