Four fire engines and around 25 firefighters tackled a fire at a detached house on Wildwood Road in Golders Green.
Most of the roof void was damaged by the fire. Three people left the building before the Brigade arrived, one of whom attended hospital.
The fire is believed to have been accidental and caused by hot works.
One of the Brigade's 32-metre turntable ladders was used at the scene as an observation tower to help fight the fire from above.
The Brigade was called at 1411 and the incident was over for firefighters at 1527. Crews from Finchley, Hendon, Paddington and Kentish Town fire stations attended the scene.