As a number of design and construction issues have been confirmed in Sydney’s cracked Opal Tower by an independent investigation — subcontractors who worked on the building have revealed some worrying details.

Australian Subcontractors Association spokeswoman Louise Stewart toldThe Saturday Telegraph workers were employed at “bargain basement prices” and claim they were not paid on time.

She said eight businesses claimed they were expected to build the tower for “unreasonable pay” and “when payment was due it was not forthcoming”.

However a spokeswoman for the tower’s builder’s Icon said the firm “categorically rejected” any claims of late payments to subcontractors.

“Icon is one of the best payers in the business,” she told the Telegraph — adding that none of the variations were “unusual”.

It comes as the independent investigation has found numerous building faults.

An interim briefing by two engineering experts, commissioned by the state government, has identified a number of problems in the Sydney Olympic Park tower.

The tower was evacuated on Christmas Eve after cracks were found in the structure with residents still shut-out of their apartments as investigations continue.

In a statement issued by the planning minister’s office, Professors Mark Hoffman and John Carter on Friday said they had identified issues that would require further investigation.

The preliminary investigation found no evidence of any issues with the foundations of the building.

“We are now able to focus our attention on these key areas to determine what has caused the issues,” the engineering experts said.

“We have also met with the engineers working on these matters and those who are working on the rectification proposals.”

Earlier in the day the NSW premier “wholeheartedly” encouraged residents to explore their legal options as some consider a class action against whoever’s responsible for the building’s faults.

Gladys Berejiklian said those found responsible for the debacle should be held accountable.

“Absolutely, I think residents should exercise every right, every legal opportunity they have, I would if I was in their shoes,” she told reporters.

Shine Lawyers class-action specialist Jan Saddler says the firm has held talks with some residents who are anxious about the state of their investment.

“It would, at a very high level at least, look like there would be grounds or the basis for bringing a class action in this particular case subject of course to what is discovered,” Ms Saddler told AAP on Friday.

“Overwhelmingly the concern and feeling is one of fear, uncertainty, then you get into those people who are very angry and frustrated.”

Ms Saddler said the law firm was awaiting the outcome of both a government inquiry into the tower problems and a review commissioned by the developer before taking further action.

People have voiced their frustration on a Facebook group for Opal Tower residents and owners over the lack of information being provided. “We still don’t have an answer to the main question about the reason of those concrete panels failures,” one person wrote in the group.

Another stated: “We thankfully do not own our apartment but I feel for people who do with this situation and can imagine how many questions people have.”

Ms Berejiklian said while she empathised with tower residents financial aid for those affected was not a matter for government.

Professors Hoffman and Carter expect to release a more comprehensive update by the end of next week.

— with AAP