Peter Grace said he was ''fired up'' Otago Girls' High School had been granted authority to demolish Greenslade Mansion, in Tennyson St.
From his living room in the historic building he was restoring - the former Temple Gallery in Moray Pl - he could see the mansion.
If the school did not intend to restore the mansion, it should sell it for the sake of Dunedin's heritage and to set an example.
''What sort of role models are they for the girls of the school? It's an important part of the city's heritage.''
Earlier this month, Heritage New Zealand (HNZ) granted authority to the school to demolish the mansion to clear land for a car park.
As part of the process, an archaeological assessment this month revealed the mansion was a ''highly significant archaeological site'', as it was built by a founder of Speight's Brewery, Charles Greenslade, who helped establish the Waipori power scheme.
''He worked hard to establish himself in Dunedin from his arrival in 1864 and much of the original mansion he built in 1887, in particular the interior decoration, fixture and fittings, which typifies his success by this time, are still present,'' HNZ senior archaeologist Pam Bain said in the authority.
The Rev Phillip Filleul built stables on the site in 1859, so a demolition condition was that any stone, cobbling or brickwork of the stable floor must be preserved.
Council heritage policy planner Glen Hazelton said the meeting was ''positive'' and he was ''stoked'' the board agreed to explore options other than demolition.
However, as the mansion was not a protected building or in a historic precinct, the council could not stop the school demolishing the mansion, Dr Hazelton said.
He was unsure why the mansion had not been protected.
''Other buildings in that street were, so it's hard to know why it wasn't registered for protection at the time.''
School principal Linda Miller said the mansion was not bought as a restoration project.
''Our priority is not doing up a building. It is to provide the best education to the girls of Dunedin.''
Mrs Miller said a previous board bought the mansion for the land so the school had expansion options.
''We are severely limited in terms of the space that we have here.''
The school had no immediate plans to expand, but if the mansion was demolished, the land would be used as a car park, she said.
The mansion is used at present as tenanted flats.
