Four fire engines and around 25 firefighters were called to the small fire at a house in Springfield Road, Wimbledon.
Part of the basement of the semi-detached house was damaged by the fire.
One woman left the property before the Brigade arrived.
The Brigade was called at 1139 and the fire was under control at 1250. Fire crews from Mitcham, Battersea, Wimbledon and New Malden fire stations attended.
The cause of the fire is believed to be accidental and due to a fault in an extractor fan.