Eight fire engines and around 60 firefighters were called to a fire on Hill Top in East Finchley.
The roof of a semi-detached house was destroyed by the blaze and most of the roof of an adjoining property was damaged. There were no reports of any injuries.
Station Commander Sacha Clement, who was at the scene, said: "Firefighters were faced with a well developed fire when they arrived.
"One of our new 32 metre turntable ladders was at the scene and was used to tackle the blaze from height."
The Brigade's 999 Control Officers took seven calls to the fire.
The Brigade was called at 0311 and the fire was under control by 0515. Fire crews from Finchley, Hendon, Hornsey, West Hampstead and surrounding fire stations were at the scene.
The Brigade’s fire investigators believe the fire was accidental and the most likely cause was hot works which had been carried out in the roof.