Passers-by sounded the alarm after they saw smoke coming from a broken window in Milbanke Way, near the Western Industrial Area.
A pump from both stations arrived at the scene at around 11.40pm and had to make a forced entry into the building by breaking down the door.
They then extinguished the fire in around 20 minutes, though the Bracknell crew remained at the scene until 1.30pm when the smoke cleared.
It is believed the fire was started by a faulty photocopier. It is not being treated as suspicious.