A Singapore-based developer has been accused of giving Sydneysiders “a two-fingered salute” after builders on one of their sites smashed down a heritage facade with sledgehammers while working on a new tower block.

Instead of preserving the 1912 Edwardian facade as they’d pledged, they left only two spindly thin separate features of the frontage of the treasured Kings Cross building, propped up with metal girders.

Now the City of Sydney has launched an urgent investigation into the illicit removal of the facade of the historic apartment building Hensley Hall at the prominent corner site, and the heritage impact of the demolition.

“It’s been gutted, with only skeletal remains left,” said Potts Point and Kings Cross Heritage Society president Andrew Woodhouse, of the front of the building which is cited a “contributory item within the Potts Point Conservation Area”. “With those two slivers left, it’s as though the developers are giving a two-fingered salute to the community.

“If a façade is heritage and protected, then it should be protected and preserved. Every brick is crucial. Instead, its significance is being destroyed. This is not a satisfactory approach to heritage at all. You can’t keep two small pieces of a facade and tear down the rest. It’s heritage heresy.”

The developer of the new eight-storey, 44-apartment building, The Hensley, intended to sit behind and over the facade of the old structure on Bayswater Road, is Singapore firm Roxy-Pacific which has recently expanded into Australia.

Development manager John Chagaris said the demolition was necessary to create openings for the new building, for the entry way and for balconies on the apartments.

Later, however, he came back to add, “Roxy-Pacific declined to comment on this matter. This is an official statement.”

A City of Sydney spokesperson said the removal of the wall was contrary to the development approval for the site.

“The city gave development consent for the demolition of the existing contributory building at 37–41 Bayswater Road, which did not include the Bayswater Road facade,” she said. “It appears some elements of the facade that were to be retained have been removed.

“The City is currently investigating the unauthorised removal and considering the heritage impact of the work undertaken.”

The architect of the new building, Domenic Alvaro, principal of Woods Bagot, speaking from New York, says as he is overseas, he hasn’t seen the site for a while.

“Structurally, they had to take a wall down, but they will rebuild it again,” he said. “They’ve had a lot of careful study with the [developer] client, the City of Sydney and the engineers over the retention of the structure. So there should be no concerns.”

But Mr Chagaris said the wall would not be rebuilt. “We’ll be integrating those two pieces left – the old gable walls – into the new building. But we won’t be rebuilding that wall.”

Meanwhile, Mr Woodhouse says he’s received numerous calls from local residents concerned about the heritage site. “There’s a groundswell of community concern about how this site is being dealt with,” he said. “It’s become innovation masquerading as conservation.

“They’re trying to give the appearance that the heritage has been retained but it’s not. And as this work is now deemed to be illegal by the council, it’s become a safety issue now, too. This isn’t what was approved.”

Already, a number of apartments have been bought off the plan, with prices ranging from $820,000 for a 39-square-metre studio, to $3.75 million for a 132-square-metre three-bedroom unit. There’s also a cafe to be built on the ground floor, with the development to be completed by December.

With the lock-out laws at the Cross, there’s been a whole new boom in the construction of new apartments out of old buildings.

Next-door neighbour Peta Wilcox, a member of the 2011 Residents Association, says she looks down on the space from her apartment.

“They’ve kept those two tiny slivers of the facade which is ludicrous,” she said. “It’s totally bizarre. I’m pretty sure this wasn’t what anyone intended. They’ve got those two little bits left which are about six inches thick, and they’ve excavated all the rest.”

Before work started on the site, Barry Minhinick, the unofficial “caretaker” of Hensley Hall who lived there for 20 years, and grew a lush garden on its side, was evicted.

“I’m realistic and practical, but it does sadden me,” he says. “I do love old buildings and the facade of Hensley Hall looked good with all the old terraces around. I’m crying into my heart because the young people won’t know about the history of the area.”