Construction employment totaled 6,166,000 in December, the highest level since March 2009, according to an analysis by the Associated General Contractors of America (AGC). The month proved a 12-month gain of 290,000 jobs, or a 4.9-percent increase.

Construction employers added 48,000 jobs in December and 290,000 for the year, the largest annual increase since 2005, as the sector’s unemployment rate fell to 8.3 percent. Association officials caution, however, that while many firms are expanding payrolls to keep pace with growing construction demand, they are having a hard time finding qualified workers to fill key positions.

“Construction firms are clearly ramping up their hiring to keep up with swelling demand for construction,” says Ken Simonson, the association’s chief economist. “Demand for workers to construct apartments, pipelines and huge industrial projects is likely to remain robust in 2015.”

Residential building and specialty trade contractors added a combined 13,500 employees since November and 132,100 (6 percent) over 12 months. Nonresidential contractors hired a net of 34,400 workers for the month and 158,200 (4.3 percent) since December 2013.

The number of workers who said they looked for work in the past month and had last worked in construction fell to 680,000 from 958,000 a year earlier, according to AGC’s analysis. The latest total was lower than in any December since 2000. In addition, the average work week for craft workers lengthened to 40.1 hours, the most since the series began in 1947, as firms ask employees to work more overtime to make up for the difficulty in finding additional workers, according to the release.