The council had contracted Wellington-based business The Building Intelligence Group to assist with the office move and subsequent fit-out of temporary premises.
The move had been made more challenging, as one building earmarked for a possible move had "dropped off the list" due to their seismic reporting criteria.
"What we do not want is to vacate one earthquake prone building only to find ourselves working from another one," Mr Jack said.
"The legislation on this changed on July 1, which makes things even more challenging, so we have had to be firm in the criteria we set for ourselves in this regard.
"We will require any building we move into to have either a Detailed Seismic Assessment report to hand, or if strengthening work has occurred in that building, an engineer's statement. Our staff are number one, and in order to ensure their safety at work, we need to be clear about what is acceptable and what is not."
So far, four staff had taken up the option to work off-site until a temporary office location was established.
The detailed seismic assessments were commissioned ahead of a planned $7 million refurbishment of the office buildings, detailed in the Long Term Plan 2015-25.
Conducted by Strata Group, they showed the Civic Administration Building met 10 per cent of NBS (New Building Standards) and the Library Building, 15 per cent.
Prior to their seismic assessment, the council had thought the civic administration building might receive a low rating, and had started working through possibilities for the transition of staff and services from that building.
However the rating for the Library Building was "certainly a surprise", Mr Jack said.
"Before the findings were returned to us, we had sketched out a few possibilities - all of which had us moving all of our Civic Building staff into the Library Building, but this is obviously no longer an option for us immediately."
The council were also considering how the library would be accessed - exploring a range of options which could see a pop-up library and customer services counter in the CBD, until decisions on a permanent library were made.
Mr Jack said the current administration buildings, including the library, would remain open for at least the next month, with the Library Building continuing to be assessed for refurbishment and strengthening, so that cost estimates are able to be presented to council for a decision on its future.