Four fire engines and around 25 firefighters were called to a fire at a church converted into houses on Tytherton Road in Islington.
Part of the first floor of a four-storey house was damaged by the fire. There were no reports of any injuries.
The Brigade was called at 0902 and the fire was under control by 1044. Fire crews from Islington, Holloway and Kentish Town fire stations were at the scene.
The Brigade's fire investigators believe the fire was accidental and caused by a fault in an extractor fan.