Four fire engines and around 25 firefighters were called to a fire at a house on Derwent Drive in Hayes.
Most of the loft and roof space of the semi-detached property were damaged by the fire. Four people left the building before the Brigade arrived. One woman was taken to hospital suffering smoke inhalation by London Ambulance Service crews.
The Brigade was called at 0400 and the fire was under control by 0724. Fire crews from Hillingdon and Southall fire stations were at the scene.
The Brigade's Fire Investigators believe the fire was accidental and involved a fault within the electrical lighting system.