An independent final report found multiple construction and design faults in the new 117m building in Sydney's Olympic Park.
The new report from 3 senior engineers, commissioned by the NSW government, found that the use of inferior materials and beams that were not designed to spec led to the damage in what as been called "the 8 seconds of cracking" on Christmas Eve.
However, the report did not lay specific blame on any of the major parties involved: developer Ecove, engineering by WSP, and builder Icon.
The building was found to be overall structurally sound, but some of the horizontal concrete "hob beams" were not up to standards of strength... or national codes.
According to the report, insufficient grout on the beams was another problem:
"Our final report confirms that a number of structural design and construction issues, including non-compliance with national codes and standards were responsible for the observed damage at Opal Tower.
"We found some of the as-constructed hob beams and panel assemblies were under-designed according to the National Construction Code and Australian Standards, leaving the beams prone to failure.
"We also found construction and material deficiencies likely contributed to the damage to the hob beams on levels 4 and 10.
"We consider that the building is overall structurally sound and the localised damage to the building can be rectified to ensure the building is compliant with the National Construction Code."
The report confirmed that most if not all of the major columns in the building had been designed such that their load capacity well exceeded expected load to be placed on them.
Still, of the 392 apartments in the building, only 170 have been declared fit for occupation. Many families are still stuck in temporary accommodation, and likely will be for weeks to come.
Some former residents said they will never return.
Among the multiple findings of construction fault:
"During our investigations, and subsequent to the issue of our interim report, records of strength for the concrete used to construct the hob beam were provided to us.
"These reveal 28 day strengths of these concrete samples as 50 MPa, where 65 MPa concrete was ordered for supply, indicating that the concrete in the hob may also have been of a lower strength."
Experts have recommended creating a database of engineer registrations and building certifications, as well as a structure review board to more closely monitor building flaws, and provide input for future building codes.
"We agree in principle with the rectification works planned to date, noting that these have advanced considerably since our interim report was released.
"However, we repeat our call for qualified structural engineers to check the final design and construction proposals in detail before major rectification works begin and before the building is deemed completely safe for occupancy, while noting the reoccupation of the building extends beyond the scope of our investigation and is a matter for residents and the builder.
Matt Kean, Minister for Better Regulation, said the government supported the recommendations.
Minister for Planning and Housing also appeared to endorse the scheme.
"We will be working through the detail of today’s report with our new Building Commissioner to make sure that when homeowners are handed over the keys to a new building, it is safe, structurally sound and free from major defects."