Thick smoke was seen coming from the roof of a house in Accrington over the weekend.
A faulty electrical fan in the property on Collingwood could have caused the incident, firefighters said.
A spokesman for Lancashire Fire and Rescue Service said: "Three crews went to the scene and used an aerial ladder platform to get access to the fire. When above the roof they removed some tiles so they could get at the fire below with a hose reel. Because of the weather they then covered the roof with sheeting to keep the weather out. It was possibly a fault with an electric fan."
The incident on Saturday, December 1 at around 5.10pm caused severe damage to the roof and light smoke damage to the bedroom and en-suite.