Former council offices in Thorne, Doncaster, were set on fire last night.
Fire crews from Thorne and Doncaster stations used an aerial ladder platform to reach the first floor blaze at the derelict premises in Ellison Street.
The incident was reported at 8.20pm and firefighters wore breathing apparatus to make sure there was no-one inside the building, which has been empty for some years.
They were there for more than an hour and used fans to ventilate the rest of the structure.
A spokesman confirmed the blaze had been started deliberately.