A highly experienced engineer says many in the industry cannot understand how cost estimates to repair Wellington's shuttered city library could be more than rebuilding it.
The library was shut suddenly in March last year due to earthquake safety fears.
A number of options are being looked at by Wellington City Council and include repairing the current building to a high standard costing about $200 million, demolishing and starting again for $160.7m, and doing less comprehensive repairs for $90.8m - but that could fail again in a substantial earthquake.
Adam Thornton has more than four decades experience as a building engineer.
He told a Wellington City Council meeting today he has spoken to major Wellington engineering firms LT McGuinness, Naylor Love, and McKee Fehl about the project.
"And they have each confirmed my view that the estimates for the strengthening and retrofit options are significantly greater on a square-metre basis than for comparable projects," Thornton said.
"It is just not conceivable that for a relatively modern building the cost of retrofit should be more than a totally new building."
The council was supposed to talk about the next steps for the library at today's meeting but in his opening remarks mayor Andy Foster said the council had decided to delay the discussion so it could get more advice.
He said while he understood residents wanted a speedy decision the council needed a little more time.
"That is to allow us to get some more guidance on a number of things. First of all the process that we need to go through to comply with the Local Government Act.
"And secondly I think we want a little more advice on the earthquake engineering seismic issues related to the building."
Foster said the pause will allow it to formulate a preferred option to take out for public consultation rather than a set of options.
Thornton endorsed the council's decision to delay going for public consolation, saying the numbers were reviewed and tested.
"Such testing should be done in collaboration with a group of builders, engineers and architects," he said.
High-profile Wellington architect Roger Walker said demolishing the building was "unthinkable".
He said it was a "poetic building" which was designed by Athfield Architects and was recognised throughout the world.
Walker said if it was knocked down that could threaten the precinct's heritage status.
Foster has previously said a future library could be at least five years away.