Eight fire engines and around 60 firefighters were called to a fire at two semi detached houses in Croham Valley Road in South Croydon.
Half of the roofs of two semi detached houses were damaged by fire. One man was treated at the scene for smoke inhalation by London Ambulance Service crews.
The Brigade was called at 1136 and the fire was under control at 1332. Fire crews from Croydon, Mitcham, Addington, Purley, Norbury and Woodside fire stations attended the scene.
The fire is believed to be accidental and caused by a failure of lithium batteries.