Four fire engines and around 25 firefighters were called to house fire on Park Hall Road in East Finchley.
The whole of a loft conversion and a large part of the roof were completely destroyed by fire. Part of the first floor of the house was also damaged in the blaze.
The Brigade was called at 1451 and the incident was under control by 1700. Fire crews from Finchley and Hornsey fire stations were at the scene.
The cause of the fire is under investigation.