Opal Tower needs 'significant' repairs

An independent review into Sydney's cracked Opal Tower has found that although the building is structurally sound it will require "significant rectification works".

Numerous construction and design problems were detailed in the review's interim report - released on Tuesday - but the authors confirmed the 36-storey building isn't about to collapse.

Ongoing investigations and repair works mean there's still no timeline for when residents can return to their apartments.

Tuesday's report by Professors Mark Hoffman, John Carter and Stephen Foster has ruled out dodgy materials and extreme weather causing the large cracks which appeared on Christmas Eve.

"While we have isolated the probable cause to localised structural design and construction issues, we need more information to make definitive conclusions about the cause or causes of the damage," the report's authors said.

"More work is also needed before we can provide recommendations on what needs to happen to avoid incidents like this in the future."

The professors visited the site multiple times during their investigation commissioned by the NSW government.

"We recommend that independent and qualified structural engineers be engaged to check final proposals in detail before major rectification works begin," they said adding it was difficult to say how long that could take.

Opal Tower body corporate chair Shady Eskander says he and hundreds of other residents want a comprehensive review of the building completed before they'll consider moving back in.

"The worst thing that can happen is that in a couple of years down the track we have an incident occur again," Mr Eskander told reporters.

"People were buying into the Australian dream and unfortunately this has become an Australian nightmare for us. We have suffered."

While his first priority is the safety and wellbeing of residents, Mr Eskander is also considering his legal options stating: "In the course of time, of course, there will be legal action."

Construction problems identified by the professors include issues with the building's hob beams.

The report found there was compelling evidence indicating the wrong size reinforcing bars were used in some areas of the building.

Prof Hoffman said while there were a number of issues outlined in the report, the authors were not yet able to identify which of them caused the building to crack.

"We have identified quite a number of what we have called construction issues but, at this stage, we have not been able to identify which of these is materially important versus the design," he told reporters.

The building's developer thanked the government for the preliminary findings and said the company's thoughts were "for the welfare of the residents".

"We need this problem to be fixed and the residents deserve to be in their homes," Ecove director Bassam Aflak said in a statement.