The number of unemployed U.S. workers with construction experience dropped to the lowest total for September since 2000.

Despite the robust demand for construction in many areas of the country, hiring continued to slow, according to an analysis released Oct. 2 by the Associated General Contractors of America. Association officials cautioned that the hiring slowdown most likely reflects a lack of available workers, which could lead to project delays unless more students and workers join the construction sector.

"Growth in the construction workforce has been slowing throughout 2015, just at the time that construction spending has accelerated to a multi-year high," said Ken Simonson, the association's chief economist. "Contractors would love to hire more workers but there aren't enough qualified craft workers or supervisors available."

Construction employment totaled 6,396,000 in September, the most since February 2009, but the total rose by only 8,000 in September and by 205,000 or 3.3 percent over the past year, Simonson noted. In the previous 12 months, construction employment had risen by 298,000 or 5.1 percent.

The number of unemployed job seekers in September who last worked in construction totaled 479,000, the lowest figure for September since 2000. The unemployment rate for such workers was 5.5 percent, the lowest September number since 2001. Meanwhile, Census Bureau data released on October 1 showed that the growth in construction spending accelerated to a nine-year high of 13.7 percent in the latest 12 months—August 2014 to August 2015—from a 2.7 percent rate a year earlier.

 "The most likely explanation for these divergent trends is that the pool of unemployed workers with construction experience has evaporated," Simonson said. "Overwhelmingly, contractors say they are having trouble finding workers to fill a variety of craft and supervisory positions."

Simonson pointed to a survey the association released in September that found 86 percent of construction firms reported difficulty filling hourly craft or salaried positions. In particular, 73 percent of firms that employ carpenters reporting trouble finding those workers. Across all 21 crafts covered by the survey, at least one-quarter of respondents reported difficulty filling each craft. Among salaried positions, 55 percent reported difficulty finding supervisors or project managers.

Association officials called on federal, state and local officials to act on measures included in the association's Workforce Development Plan such as increased funding for career and technical education and an end to restrictions on cooperative training programs to rebuild the pipeline for recruiting and preparing future construction professionals.

"Too many school systems are not providing students with opportunities to explore high-paying, in-demand careers like construction," said Stephen E. Sandherr, the association's chief executive officer. "Unless federal, state and local officials give educators, employers and associations greater flexibility and resources to set up career and technical educational training programs, we are likely to see construction costs go up and schedules get delayed."