Four fire engines and 21 firefighters and officers were called to a fire at a house in Woodhall Avenue in Pinner.
Part of the roof of the detached property was damaged by fire.
Two people left the property before the arrival of the Brigade. There were no reports of any injuries.
The Brigade was called at 0940 and the fire was under control at 1046. Fire crews from Harrow, Northolt, Stanmore and Ruislip fire stations attended the scene.
The cause of the fire is under investigation.