Police are investigating after a house in South Oxhey was left badly damaged when a large fire broke out last night.
Fire crews from Watford, Garston and Rickmansworth were called to the blaze in Gosforth Lane at around 8pm.
Watch commander Dave Elliott, from Watford Fire Station, said the fire had taken hold of the roof by the time firefighters arrived.
He said: "When we arrived, there was a serious fire in the roof. It had broken through the roof and was emerging onto next door so we quickly got hoses onto it.
"We had four firefighters with breathing apparatus inside the house and then three jets and a hose reel to extinguish the fire from outside.
"We also had an aerial platform, although we did not use it for fire fighting but to provide emergency lighting."
Mr Elliott added the fire left extensive damage to the upper part of the house.
Hertfordshire Constabulary confirmed this morning it had launched an investigation in connection with the fire.