Fire safety officer Barry Gibson said last Wednesday's fire in a Somerville St house, which damaged most of the top storey of the five-bedroom home, started in a couch in the living room.
He was still working on the cause of the fire, but said it spread quickly and consumed the living room within moments.
The family had given permission for the house to be opened to the public on Saturday so others could see the effect of the fire, he said.
A Monday night fire at a Daly St house in Port Chalmers, which gutted the single-storey wooden villa, started in a bedroom.
Mr Gibson had not yet determined the cause of that fire.
He considered neither fire was suspicious.
The occupant of the Daly St house declined to comment.
