Six fire engines and around 40 firefighters were called to a fire at a house on Winn Road in Eltham.
Part of the loft conversion and roof of the detached property were damaged by the fire. A man, a woman and two children left the building before the Brigade arrived. There were no reports of any injuries.
The Brigade was called at 1156 and the fire was under control by 1327. Fire crews from Lewisham, Forest Hill, Greenwich and Sidcup fire stations attended the scene.
The Brigade's fire investigators believe the fire was accidental and was caused by the failure of an electric extractor fan fitted above the shower.