Four fire engines and 21 firefighters and officers were called to a fire at a house in Dryden Road, Harrow.
Most of the roof of a mid-terraced two-storey house was damaged by fire.
A woman and four children left the property before the arrival of the Brigade.
The Brigade was called at 1836 and the fire was under control at 1942. Fire crews from Stanmore, Harrow and Northolt fire stations attended the scene.
The cause of the fire is under investigation.