Construction costs accelerated again in May, with steep increases for a wide range of materials, according to the Associated General Contractors of America. Those materials include many that are subject to tariffs that could drive prices still higher.

"Prices jumped at double-digit annual rates for metals, lumber and plywood, and diesel fuel, while ready-mixed concrete, asphalt paving, and roofing materials also had unusually large increases," said the association's chief economist, Ken Simonson. "The cost of all goods used in construction rose 8.8% from May 2017 to May 2018, the steepest annual increase in nearly seven years."

From May 2017 to May 2018, the producer price index jumped by 17.3% for aluminum mill shapes, 13.9% for lumber and plywood, 13.8% for copper and brass mill shapes, and 10.5% for steel mill products. Other construction inputs that rose sharply in price from May 2017 to May 2018 include diesel fuel, 44.5%; asphalt felts and coatings, 8.9%; ready-mixed concrete, 6.5%; and paving mixtures and blocks, 5.2%.

The U.S. imposed steel and aluminum tariffs on imports from Canada, Mexico, and the European Union on May 31. The impact from these tariffs is not reflected yet in the most recent data.

"These increases far outstripped the 4.2% rise in the price index for new construction, implying that contractors are facing a severe squeeze on costs for both ongoing and new projects," Simonson added. "Moreover, tariffs imposed on steel and aluminum since this data was collected in mid-May are likely to drive contractors' costs still higher."

The producer price index for inputs to construction industries, goods — a measure of all materials used in construction projects including items consumed by contractors, such as concrete products — rose 2.2 % in May alone and 8.8% over 12 months. The year-over-year increase was the steepest since July 2011, the economist noted.

Even before they have taken effect, construction officials said the tariffs have triggered a surge of orders that mills say exceeds their current capacity, a situation that threatens to produce construction delays, budget problems, and possibly cancellations for future construction projects.

"Considering the impact the mere threat of tariffs have had on materials prices and demand, prices are likely to increase further as the new trade restrictions come online," said Stephen E. Sandherr, the association's chief executive officer. "Forcing contractors to pay more for materials and wait longer to receive them will make construction more costly and slower."

View producer price indexes for construction.