Courts in Northern Ireland are empty almost half the time, an inspectorate said.
The Northern Ireland Courts and Tribunals Service (NICTS) is considering closing eight venues to save money.
A watchdog said the amount of time venues are in use has decreased and it supported efforts to shut outdated centres.
The Criminal Justice Inspectorate said: "Whatever action the NICTS decides to take, the facts remain that utilisation has fallen and the cost of maintenance and the need to upgrade the court buildings to meet modern standards is beyond the resources available to the NICTS.
"Retaining the current estates infrastructure is not an option."
The inspectorate acknowledged progress in developing the estate strategy but said the buildings are of mixed suitability. It highlighted a fall in the average rate of use from 67% to 56% and said the reduced funding required immediate action.
"The NICTS could consider the reduced utilisation at Laganside and Lisburn as an opportunity to transfer business from a court building (Lisburn) that has very poor custody accommodation and vehicle access to one of the most modern courts in the NICTS estate.
"Similar conditions pertain in the case of Armagh and Newry courts and these changes could be implemented without influencing the longer term proposals for the remainder of the estate."
Justice minister David Ford is proposing to close hearing centres in Limavady, Strabane, Enniskillen, Magherafelt, Ballymena, Newtownards, Armagh and Lisburn in a bid to absorb an 11% - £2.3 million - annual funding cut to the courts service.
The service has already shut courts in Bangor and Larne.
The follow-up review from the inspectorate found three strategic and three operational recommendations had been fully achieved, with a further four recommendations partially achieved since the publication of CJI's original report on the adequacy of the courts estate in Northern Ireland in 2012.
Chief inspector Brendan McGuigan said: "Inspectors support the actions taken over the last three years by the NICTS to close a number of outdated, expensive, under-used courthouses and hearing centres and would urge management to make any future decisions around rationalisation of the courts estate on affordability and need.
"We also welcome the work undertaken by the NICTS to bring forward proposals to create three new court divisions. This work maximises opportunities for existing accommodation to be shared with other Department of Justice bodies, while ensuring the facilities best meet the needs of those who use them and fulfil statutory requirements."