SUNLIGHT magnified through a window started a garage blaze.
But the flames were already out when firefighters arrived at Ringshall, near Berkhamsted.
The resident had used water from a hose pipe to put out the fire inside the brick-built garage at the rear of the property.
Two crews from Hemel Hempstead were called to the home just after 6pm on Saturday.
Firefighters dampened down to make sure the fire was fully extinguished before leaving the scene.