The company that built Sydney’s Opal Tower is embroiled in another safety scare at a different city apartment block.

Residents of Otto Rosebery have been warned against leaning on their balconies or allowing more than three people to stand on them, after an investigation found the balustrades were of “inadequate strength”.

Parents have been warned not to let children play on balconies.

And now owners have flagged the possibility of pursuing the builder and developer in the Supreme Court.

The four-year-old building, comprising 298 units, is built by Icon Co – the same builders behind the now-infamous Opal Tower where major cracks led to an evacuation on Christmas Eve last year.

In an “urgent” safety letter, seen by The New Daily, residents were told the owners’ corporation had received expert advice the balustrade system was “structurally defective”.

A subsequent notice from strata management said “all possible precautions should be taken to avoid purposeful or accidental leaning”.

Warning notices have been plastered on balcony doors.

Otto Rosebery from ICON CO on Vimeo.

The revelation comes after a series of high-profile defect scares and evacuations that has shone a spotlight on poor workmanship and lack of oversight within Australia’s building industry – with problems reported nationwide.

In July, residents of Melbourne’s Australia 108 building reported significant movement and large cracking sounds in what is set to become Australia’s second-tallest building.

In the same month, it was revealed that more than 100 home owners were told they could not move into their newly constructed units in Erskineville, in Sydney’s inner south-west, amid concerns the block was built on contaminated ground.

Weeks prior to that, hundreds of people were evacuated and left homeless after cracks appeared in the facade of the Mascot Towers, also in Sydney. The repair bill is expected to be more than $20 million.

It’s not known how the issues with the Otto balconies were originally reported to the owners’ corporation, which would not answer specific questions about the safety concerns on Tuesday.

But an inspector from Broune Group, which specialises in investigations into structural defects and failures, was called out to the property to check the integrity of the building.

They found the aluminium posts that support the balustrades and glazing did “not comply with the requirements of the Building Code of Australia and Australian Standards”.

Builders Collective of Australia president Phil Dwyer said residents might not have realised there was a problem, as “serious” structural issues required a trained eye.

But he warned those failing to heed the safety warnings that the owners’ corporation and strata management “wouldn’t have put out that notice without justification”.

Labor MP for Heffron Ron Hoenig said it was shocking that an apartment block could be built with non-compliant balconies.

“How does a building get constructed where there is something wrong with the balustrade and something wrong with the weight you can put on balconies?” Mr Hoenig asked The New Daily.

“This is just the tip of the iceberg … the whole building industry, particularly in New South Wales, is in crisis.”

In response to a list of questions from The New Daily, Hugh McCormack of McCormacks Strata Management said the issue was currently being “litigated”.

“The owners corporation are working productively with the defendants to resolve any issues,” Mr McCormack wrote in an email.

“The owners corporation will not be providing any further information, under advisement from its legal representatives, and any and all information provided to the owners corporation is privileged and confidential.”

The original advice letter to Otto apartment owners, from PRDnationwide Norwest, said the owners’ corporation would be “notifying the builder and developer … and, to the extent necessary, seeking to include the balustrade system within the existing Supreme Court proceedings relating to defects”.

In July, a class action was launched by Opal Tower owners, who are seeking millions of dollars in compensation.

Documents lodged with the NSW Supreme Court suggested the owners were suing the NSW government and Sydney Olympic Park Authority (SOPA), the owner of the land on which the Opal Tower sits.

But last week, The Australian Financial Review reported that Icon and Opal’s developer Ecove had also been drawn into the case.

Mr Hoenig said the cracks in Australia’s construction industry ran so deep that only a royal commission could begin to fix them.

Icon Co did not answer questions or return numerous requests for comment on Tuesday.