Six fire engines and around 40 firefighters were called to a fire on Manston Avenue in Southall.
Part of a roof of a two storey detached house was destroyed by fire and a small part of the first floor.
One man was treated on scene by the London Ambulance Service and taken to hospital.
No working smoke alarms were found in the property. A London Fire Brigade spokesperson said: “This incident shows just how important it is to have working smoke alarms fitted on every level of your home.
“Smoke alarms give the earliest possible warning when a fire starts and we would urge everyone to make sure they have one fitted in every room where a fire can start except kitchens or bathrooms where heat alarms are more appropriate.”
The Brigade was called at 0538 and the incident was over by 0737. Fire crews from Southall, Heston, Hayes and Feltham fire stations were in attendance.
The cause of the fire is accidental and due to resistive heating in a bathroom extractor fan.