Four fire engines and around 25 firefighters were called to a fire at a house on Stanford Road in Norbury.
Part of the roof extension of the mid-terraced two-storey house was destroyed by the fire. One man left the property before the Brigade arrived and was treated at the scene by London Ambulance Service.
The Brigade’s Control Officers took fifteen 999 calls to the incident.
The Brigade’s Fire Investigation team believe the fire to be caused by a gas torch and roof adhesive.
A Brigade spokesperson said: “Different adhesives can react to heat and flames, it is likely in this case that the glue reacted to the heat of the gas torch and caused a fire.
“If you are using a gas torch near any adhesives, please ensure you read the manufacturers instructions in order to prevent future fires like this happening.”
The Brigade was called at 1153 and the fire was under control by 1405. Fire crews from Norbury, West Norwood, Tooting and Mitcham fire stations attended the scene.