The courthouse was deemed an earthquake risk last November. Since March, district court cases in Oamaru have been heard in the town's opera house.
Agreement on how much it will cost to strengthen the historic building has still to be reached.
A spokesman for the ministry yesterday said a more detailed assessment of building costs would start soon.
"Opus International has been commissioned to conduct further work to determine strengthening options and costs for the Oamaru courthouse," he said.
"It is a complicated job that will require extensive collaboration with the New Zealand Historic Places Trust given the heritage one status of the building. It is likely that taking geotechnical and core samples and analysing them will take at least eight weeks and work on a detailed cost estimate cannot begin until that is done."
Last month, estimates from the Ministry of Justice put the strengthening cost at $5 million, but the ministry agreed to look again at the estimate after Waitaki Mayor Alex Familton suggested the job could be done for a 10th of that price.
