The easily carved stone has also been used to create a number of elaborate neo-classical style buildings in the main street, including the Forrester Gallery, Oamaru Opera House and North Otago Museum.
Mr Hope said imposing a 15-year timeframe to strengthen buildings would have a massive impact on the town. It would lead to demolition by neglect.
The trust, which owns 17 buildings, had already brought several buildings up to the 33 per cent strengthening standard, but assessments alone cost between $5000 and $10,000 on buildings still to be strengthened.
Mr Hope said the trust relied on grants and rentals from its buildings, which returned a modest $40 to $45sq m. Retailers in Auckland's Queen St pay upwards of $2000sq m for prime space.
"We are not opposed to the notion of strengthening. We think 33 per cent is a good basis to aim for. It's the timeframe to achieve it.
"If the country, after 30 or 35 years, has got most, if not all, of its unreinforced masonry buildings up to 33 per cent then that will be a wonderful result," he said.