Waring remained in the house for a short time, watching the sofa begin to smoke and burst into flames before leaving and walking home.
At the time, fire safety officer Stuart Cradock said the house had been severely damaged and most rooms were completely gutted.
The fire was treated as suspicious and police questioned a number of people, however it was not known whether Waring was among them.
Neighbour Joanna Cox said at the time she heard a loud cracking sound before seeing the house "engulfed in fire" with "flames way above the roof, just like in the movies".
Then, on July 29 this year, Waring, who was then employed as a handyman, approached Rotorua police and said he wanted to confess to lighting a house fire.
During his police interview he said he entered the house "because he was cold and hungry" and had not planned to start the fire.
However, after eating the pie he "felt the urge" to light the fire. Waring told police he had been feeling angry about the way the house occupant had treated his sister.
It is unclear from the summary of facts what prompted Waring to give himself up. However, he told police he was now remorseful and wished he had never done it.
Waring was living in Rotorua at the time of the arson and confession but has since moved to Auckland where he is living with his father and stepmother.
At Waring's sentencing, Judge McNaughton said 2-3 years in prison was the typical starting point for an arson sentence.
But he added: "In this case we have not only the guilty plea but also a confession before that. In my view this is an additional factor in reducing the sentence."
Prison would definitely be disproportionately severe, Judge McNaughton said.
Waring's defence lawyer Jeremy Sutton said Waring had anxiety issues and his family were concerned about him being at home for a prolonged period of time.
Judge McNaughton noted there was a history of depression in the family and Waring had been responding well to counselling.
"I will keep that sentence of home detention as low as I can, bearing in mind it will be hard - with your father and stepmother serving that sentence with you."
While the fire was not premeditated, arsonists commonly light fires as expressions of anger, Judge McNaughton said.
"I accept that you were remorseful and that if you continue with counselling you will be at a low risk of reoffending," he said.
Waring's father declined to comment on the sentence or what provoked his son's confession.
