Four fire engines and 21 firefighters and officers were called to a fire at a bungalow under refurbishment in Bourn Avenue, Uxbridge.
The roof of a detached bungalow was destroyed and half of the ground floor was damaged.
The Brigade was called at 1128 and the fire was under control at 1243. Fire crews from Hillingdon, Hayes and Southall fire stations attended the scene.
The cause of the fire is under investigation.