Six fire engines and 35 firefighters and officers were called to a fire at a house in Corringway, Ealing.
The loft conversion was destroyed and part of the first floor was also damaged. There were no reports of any injuries.
The Brigade's 999 Control Officers took 12 calls to the blaze.
The Brigade was called at 1040 and the fire was under control at 1259. Fire crews from Ealing, Park Royal and Wembley fire stations attended the scene.