The new report identified a lower than expected flexibility in the pre-cast floor and associated reinforcing walls.
Earthquake engineering experts estimated that the performance had an earthquake-strength New Zealand Building Standard of less than 34 per cent.
Hastings District Council chief executive Nigel Bickle said while HDC had not expected the report to raise issues, it understood that modelling had evolved since the Christchurch and Kaikoura earthquakes.
Bickle also said the safety of staff was at the centre of HDC's decision to vacate the building.
"While there is no requirement to vacate the building at this stage, we feel that as an employer and given the low NBS per cent, our obligation is to the safety of our staff, and their peace of mind," he said.
In the short term, staff will work from home or appropriate alternative locations.
The council advised its staff and the building's tenants on Friday and planned to have relocated its employees by Wednesday.
A strategic review will begin to evaluate the situation, including developing a plan for the building's future.