Four fire engines and around 25 firefighters were called to a fire at a house in Westbury Avenue, Southall.
Watch Manager Ian Hurry, who was at the scene, said: "We could see flames coming through the roof as we arrived and crews worked hard to stop the fire from spreading to the neighbouring properties."
Half of the first floor and the whole of the roof was damaged by the blaze. A woman left the property before the arrival of the Brigade. She was treated at the scene by London Ambulance Service crews and taken to hospital.
The Brigade was called at 0136 and the fire was under control at 0238. Fire crews from Southall and Northolt fire stations attended the scene.
The cause of the fire is believed to be electrical.