Six fire engines and 35 firefighters and officers were called to a house fire caused by a lightning strike in Princes Road in Romford.
The whole of the second floor loft room and half of the first floor of the property were damaged by fire.
Two men, one woman and one child left the property before the arrival of the Brigade. One man was treated by London Ambulance Service crews for an unrelated medical condition.
The Brigade was called at 0102 and the fire was under control at 0329. Fire crews from Romford, Harold Hill, Dagenham and other surrounding fire stations attended the scene.