Knauf Insulation in Shelbyville plans to lay off 100 workers for at least six months as a slowdown in building projects continues to hamper demand for its products.

The company notified the Indiana Department of Workforce Development of the layoffs Wednesday.

Knauf expects to begin letting go employees the week of June 6 and anticipates they will be off work for at least six months. The company is unsure at this time whether the layoffs will be permanent.

“The economic recession continues to have a tremendous negative impact on the entire building materials market,” Cindy Allen-Stuckey, Knauf’s director of human resources, wrote in its notice to DWD. “The down markets, coupled with excess inventory, have forced Knauf Insulation to make strategic production adjustments in order to keep supply in line with demand.”

The company makes thermal and acoustical fiberglass insulation for residential, commercial and industrial building applications. Its two plants in Shelbyville employ roughly 500 workers, making the German firm one of Shelby County’s largest employers.

Knauf has been forced to reduce its work force the past few years. In December 2008, the company laid off eight of its 118 corporate employees and let go 65 hourly workers.

Knauf’s U.S. operations employ about 1,250. Knauf came to Shelbyville in 1978 when it bought a fiberglass factory.