Eight fire engines and around 60 firefighters were called to a fire at a house on Bedford Road in Ealing.
The roof of the three-storey detached house was destroyed and part of the first floor was damaged by fire. There were no reports of any injuries.
A London Fire Brigade spokesperson said: "Smoke alarms fitted inside the property alerted the resident to the fire, who saw smoke coming from a cupboard in the bathroom on investigation.
"Firefighters arrived to find smoke coming from beneath the tiles of the roof and cut away parts of the walls to access the fire and bring it under control."
The Brigade was called at 1013 and the fire was under control by 1437. Fire crews from Chiswick, Acton, Hammersmith, Richmond, Kensington and other surrounding fire stations were at the scene.
The Brigade's Fire Investigators believe the fire was accidental and caused by an electric hot air gun.