It happened Tuesday morning on the roof of Chesterfield Elementary School along Thorn Lane in Chesterfield.
The superintendent told Action News that construction workers were welding on the roof when the fire started.
Part of the roof was damaged by the fire, while other sections were damaged by smoke and water.
One firefighter was taken to a local hospital and treated for a minor hand injury.
The school was not occupied with students because it is not yet finished. It is slated to open in September, and officials did not know if the fire would force them to move the timetable back.
