The options include strengthening it to various levels of the National Building Standard or demolishing it and starting again.
The most expensive strengthening option would come in at just under $200m, which is more money than any of the new build options would cost.
At a full Wellington City Council meeting held via Zoom today Foster said the paper would be adjourned until next week.
But public participants wanting to make submissions on the subject were still heard.
Structural engineer Adam Thornton said the retrofit design proposals were on the conservative side and included significant built-in contingencies.
"That is to say the engineers have allowed for unknowns and worst-case scenarios with their design, that's not a bad thing, but it is important the extent of contingency is identified so that a realistic cost can be prepared."
Thornton said such contingencies could result in inflated cost estimates.
He and other engineering firms agreed the estimates for the strengthening and retrofit options were significantly greater on a square metre basis than for comparable projects, he said.
"It is just not conceivable that for a relatively modern building that the cost of retrofit should be more than a totally new building."
Architect Roger Walker also questioned the cost estimates.
"I am incredibly unbelieving of the costings that have risen out of new build versus retention of the existing building."
Walker said it boiled down to a matter of risk aversion.
"We just have to get things in proportion, for people visiting the library, in my view, they're more likely to be hit by a bus or be killed driving to the library than the actual risk they have within the library."
Both Walker and Thornton supported the numbers being reviewed and tested ahead of public consultation.
Councillors had a question and answer session with engineers over the library yesterday afternoon but it's understood they still have queries.
Foster acknowledged the paper on the library was of huge significance to everyone.
"It's been very loud and clear that people want us to make a decision on that as quickly as we can."
Foster said the intention was now to consult with the community on a preferred option for the library's future rather than a set of options.
Libraries portfolio holder councillor Fleur Fitzsimons said she supported the mayor's call to delay the decision.
"An extra week will give him time to work with council staff and councillors to determine the steps needed to get the library open as soon as possible.
"We should consider amending the council's 10-year budget to ensure the initial design work on fixing the library can start this year."
Former Wellington city councillor Helene Ritchie told the meeting people were reeling at the proposed cost of $200m to strengthen the library.
"We have a building which sits empty, barricaded in the heart of Wellington, a sad symbol of council's ineptitude and paralysis.
"It is simply inconceivable how a request for a relatively minor "fix" has become another unaffordable $200 million vanity project, with the overblown options, cost and ambition, of virtually a rebuild internally, or demolition and a new build."
Ritchie urged councillors to urgently fix the library in the most cost effective way and reopen it.
Architectural Centre member Kate Linzey noted the building was an award winning one that was ground breaking when it opened in 1991.
"It transformed ideas of how libraries should be made and how libraries would be occupied.
"It's a post modern building which means it's quite playful and perhaps doesn't have the gravitas that we might associate with pre-war New Zealand architecture, it is a fun building."
