Firefighters responded to Litchfield High School on Plumb Hill Road for a two-alarm fire Friday.
The fire started on the roof and was reported a little after 12 p.m., according to Litchfield County Dispatch.
The Fire Marshal's Office said the fire was ignited by contractors working on the roof.
The blaze extended to part of the library. Crews said they stretched lines into the library, checked for extension into the ceiling and deployed salvage tarps to protect as many books as possible.
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The school was evacuated and there are no reports of injuries, dispatchers said. The fire was placed under control within 20 minutes.
A Tweet from school officials said the all clear was given for students to return and gather materials for dismissal.
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There was no damage to the inside of the school. Several nearby fire departments responded.
