Four fire engines and around 25 firefighters were called to a fire at a terraced house on Mason Avenue in Harrow.
Half of the first floor and half of the roof were damaged by the blaze. There were no reports of any injuries.
The Brigade's 999 Control Officers took 13 calls to the fire.
The Brigade was called at 1410 and the fire was under control by 1515. Fire crews from Harrow, Stanmore, Northolt fire stations attended.
The fire is believed to be accidental and caused by an electrical fault.