Five people had a lucky escape after a fire in an outbuilding attached to their house on Waverley Avenue in Wembley.
A brick-built extension attached to the back of the house was destroyed by the fire and part of the ground and first floor of the house were damaged as well as a small part of an adjacent property.
Three adults and two children left the property before the Brigade arrived. There were no reports of any injuries.
Watch Manager John Baldwin, who was at the scene, said: "It was only thanks to the quick thinking of one of the occupants who was woken by the sound of the fire that she alerted everyone and got them out.
"While there were smoke alarms in the house, there were none in the extension. This goes to show the importance of having smoke alarms fitted in all areas of your home.
"Smoke alarms give the earliest possible warning of a fire and we would urge everyone to make sure they have one fitted on every level of their home and in every room where there is a risk of fire, except kitchens or bathrooms where heat alarms are more appropriate."
The Brigade was called at 0609 and the fire was under control at 0725. Four fire engines and around 25 firefighters from Wembley, Park Royal and Northolt fire stations attended the scene.
The cause of the fire is under investigation.