Four fire engines and 21 firefighters and officers were called to a fire in an outbuilding in North Hill, Hornsey.
The timber-framed building was destroyed by fire. Part of the garden fencing was also damaged by the blaze.
Neighbours called the Brigade when they smelt smoke and saw flames coming from the building.
The Brigade was called at 0426 and the fire was under control at 0604. Fire crews from Kentish Town and Hornsey fire stations attended the scene.
The cause of the fire is under investigation.