Jarrod Arthur Phillips, 19, was jailed for 10 months in December for setting fire to a Housing Tasmania property in Buffalo Court, Ravenswood, in August.

He pleaded guilty in the Supreme Court in Launceston this morning to an earlier count of arson for encouraging the youth to set the Warring Street unit alight in January last year.

The youth broke into the unit and doused it with petrol before setting it alight with Phillips' lighter.

``Mr Phillips in this case was aiding and abetting, perhaps instigating, his young friend to start the fire, but he did not set foot on the property nor douse it in petrol,'' defense counsel Adrian Hall said.

The fire caused $100,000 damage before it was put out by Tasmania Fire Service.

Crown prosecutor Alan Hensley said the youth hatched the plan with Phillips while drinking at another house on Warring Street earlier that day.

Phillips and the youth returned to the property to when firefighters were putting out the blaze and were questioned by police.

Mr Hensley said Phillips later retrieved the petrol can used to set the fire and hid it in the clothes dryer of his friend's Warring Street property and it was found during a police search.

Phillips will be sentenced at 4pm on Monday.