Six fire engines and around 40 firefighters were called to a fire at a derelict hotel on Seven Sisters Road in Manor House.
The blaze damaged half of the second floor and the roof. A small part of the first floor was also damaged by fire.
The Brigade's fire investigation team believe the fire was accidental and due to the unsafe disposal of smoking materials.
The Brigade was called at 0108 and the fire was under control at 0300. Fire crews from Holloway, Stoke Newington, Tottenham, Kentish Town fire stations attended the scene.