The number of unemployed workers with construction experience dropped to the lowest total for September since 2000, as hiring continued to slow despite robust demand for construction, according to a recent analysis by the Associated General Contractors of America.

“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% over the past year, Simonson noted. In the previous 12 months, construction employment had risen by 298,000 or 5.1%.

The number of unemployed jobseekers 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%, 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% in the latest 12 months—August 2014 to August 2015—from a 2.7% 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% of construction firms reported difficulty fillinghourly craft or salaried positions. In particular, 73% 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% reported difficulty finding supervisors or project managers.