Owners were doing maintenance work when they noticed smoke coming from one of the buildings.
The insulated foam panels, on the inside of the building, were on fire.
Owners grabbed a water hose, to keep the fire under control, until DeKalb Fire Department arrived.
No one was injured.
"Well, the two outside doesn't have any lumber in them, the middle does. So, we're trying to get that lumber out just in case we have a re-ignition tonight after dark," said Steve Simpson, owner of Simpson Lumber and Sawmill.
About 30,000 feet worth of wood was in one of the buildings that caught fire.
It took workers about 30 minutes to remove it from the building.