The fire started at the rear and spread through the interior, gutting the back half of the house.

The owner was asleep but woke up when his smoke alarms went off.

Three brigades from the Tasmanian Fire Service attended the scene, but by the time they got there the building was well alight.

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Legana brigade chief Michael Clifford said the blaze took about an hour to get under control.

The house was built in the mid- 1800s and was weatherboard with plastic cladding.

Mr Clifford said the combination of materials made the fire more difficult to control as both layers were burning.

Tamar District field officer Ben Wilson said the smoke alarms might have saved the owner's life.

He said a lawnmower battery was plugged into a car battery charger inside the house, and a malfunction of some sort had set the house alight.

Mr Wilson said the structure of the house looked sound from the outside but it would probably be demolished.

The house, in Rosevears Drive looking over the Tamar River, was insured.