Four fire engines and around 25 firefighters attended a fire on Douglas Road in Brondesbury.
Part of a staircase within a terraced house under construction was damaged by fire. There were no reports of any injuries.
The Brigade was called at 1839 and Control Officers mobilised crews from West Hampstead, Paddington and Willesden fire stations to the scene. The fire was extinguished by 1951.
The cause of the fire is being treated as accidental.