Critical support beams in Sydney's Opal Tower were left susceptible to "bursting" because they were under-designed and some made from lower strength concrete, an independent report has found.
The newly-built block in Sydney Olympic Park was evacuated on Christmas Eve after cracks were found in the building, sparking fears it could collapse.
A NSW government-commissioned report, released publicly on Friday, found that while the building was structurally sound overall, there were several structural and construction issues responsible for the damage.
Horizontal support beams in the building were of inferior strength and were not compliant, while the decision to only partially grout between the beams and panels added to the problem.
"We found some of the as-constructed hob beams and panel assemblies were under-designed according to the National Construction Code and Australian Standards," professors Mark Hoffman, John Carter and Stephen Foster said.
"This left the hob beams susceptible to failure by shear compression and bursting."
Testing also showed lower-strength concrete was used in some hobs on level four, which "likely precipitated the observed major damage".
NSW Minister for Better Regulation Matt Kean said the tower's builders Icon and developers Ecove would be liable for the defects.
"We'd encourage people to get independent legal advice," he told reporters.
Planning Minister Anthony Roberts described the Opal Tower debacle as "a most harrowing and nerve-racking situation".
"Residents will work through remaining safety concerns with the builder," Mr Roberts said.
The engineers' report recommended creating databases of registered engineers and NSW building certifications, along with a building structure review board to monitor known property design flaws and shape future building codes.
Mr Kean said the government had already committed to creating a database of registered engineers.
About 150 of the building's 392 units remain empty, with the report recommending a host of repair work take place before occupants move back in.
Urban Taskforce - a body representing property developers tentatively supports some of the report's recommendations, including the call for registered engineers and third party checks "depending on how 'major projects' and 'critical stages' are defined".
The tower's builder Icon, and developer Ecove, were criticised by residents through December and January after some people were moved back in and then asked to leave again.
It's unclear how long remedial works will take to complete.