Six fire engines and around 40 firefighters were called to a fire at a house on Hallswelle Road in Golders Green.
Part of the loft conversion of a semi-detached house was damaged by the fire and a small part of the roof was damaged. There were no reports of any injuries.
Hendon Station Officer Luke Gibbs, who was at the scene, said: "Crews were faced with a significant amount of smoke issuing from the roof of the property on arrival.
"Firefighters worked hard in very hot conditions to tackle the blaze which was in the loft voids between two semi-detached houses.
"They were able to stop the fire spreading and limited the damage to the adjoining property."
The Brigade was called at 1940 and the fire was under control by 2118. Fire crews from Hendon, Finchley, West Hampstead and Paddington fire stations were at the scene.
The cause of the fire is under investigation.