Fire officers were called to a blaze in a detached house in Harefield Road, Uxbridge, on the afternoon of Monday, July 28 - the second domestic fire in the borough in hours.
A smoke alarm alerted a woman to the blaze who left the house before the arrival of the fire brigade. She was uninjured.
About half of the ground floor of the house was badly damaged.
It had been a tough day for the fire and rescue service: flash flooding caused by torrential rain required officers to rescue stranded motorists and check on properties threatened by the rising water.
After the Harefield Road blaze, a London Fire Brigade spokesman said: “A working smoke alarm is essential as it provides vital time to escape if there is a fire. Every home should have at least one working smoke alarm.”
Firefighters from Ruislip, Northolt and Southall fire stations attended. They were called at 3.30pm and the fire was under control by just after 4pm.