More than a decade before the deadly Grenfell tower fire in London, Australian suppliers of aluminium composite cladding knew the product they were selling with a polyethylene (PE) core was highly flammable.

Key points: Cheaper PE-core cladding installed in Australian buildings despite more fire-resistant cladding's availability

Cheaper PE-core cladding installed in Australian buildings despite more fire-resistant cladding's availability Preliminary audit identified 1,011 buildings in NSW that require investigation

Preliminary audit identified 1,011 buildings in NSW that require investigation Supplier says "hundreds of thousands of square metres" of cladding could have been used before 2000

Despite more fire-resistant cladding being widely available in Europe and the USA, the cheaper PE core cladding continued to be installed on medium and high-rise buildings in Australia until 2013.

A Four Corners investigation has revealed that some international manufacturers and their Australian suppliers were aware of the risks associated with using PE cladding on high-rise buildings, but they continued to import it because Australia's lax and ambiguous building standards allowed it.

Australia — in the grip of a once-in-a-generation building boom — now has a large legacy of buildings swathed in the potentially deadly material.

The number of affected properties is unknown but could be in the thousands, with a preliminary audit in NSW alone identifying 1,011 buildings that require investigation.

There could be thousands of home owners who are living in unsafe apartment buildings who face multimillion-dollar bills to fix their buildings.

A boon for architects

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Aluminium Composite Material (ACM) began to be imported in the late 1970s and quickly became popular with architects because of its versatility, light weight and modern look.

By the early 2000s it was gracing new high-rise developments, such as Jackson's Landing* in Sydney, apartment blocks in Docklands in Melbourne and several public buildings such as Fremantle Maritime Museum.

PE core cladding, which was originally developed for signage, was initially the main product imported.

But by 2000, at least one Australian supply company swapped to importing a product with a more fire-resistant core, after the manufacturer in Japan showed them fire tests comparing fire resistant and PE cladding.

Before that date, the Sydney supplier, Stephen Geddes, acknowledges that "tens of thousands of square metres … if not hundreds of thousands of square metres" of polyethylene core cladding had already been used on buildings.

And, despite the risks having been identified, other companies continued to import and install the more highly flammable product.

Ambiguous standards combined with poor enforcement

It is not illegal to import PE cladding or use it in certain situations.

But most types of cladding on the market fail the main test used to determine combustibility.

While combustible material is not strictly allowed on multi-storey buildings, even that is not black and white.

It is possible for an expert to sign off that a building meets the code if other safety measures are in place.

Fire engineer Tony Enright says regulations have not kept up with the speed of development.

"Things have descended to the lowest common denominator," he said.

"As soon as there's an obstacle to a development, [the attitude is] 'oh well, let's fire engineer it away'."

Most states have moved to a system of private certification where the building certifier is employed directly by the builder, rather than the council inspecting the building.

The ambiguous standards are combined with poor enforcement and, some say, a conflict of interest between safety and economy.

"We have, if you will, a builder, a certifier and a fire engineer who are incentivised to reduce cost," Mr Enright said.

"The builder because it's going straight on to their bottom line; the certifier because they want repeat work from the builder; the fire engineer because they want repeat work from the certifier and the builder.

"And so they're all taking risks. It's the building owners who bear those risks."

Added strain on fire departments

Aluminium-composite cladding was used on the Lacrosse building that caught fire in 2014. ( Audience submitted: Wade Savage )

The number of potentially dangerous buildings around the country has put added strain on fire authorities.

They got a glimpse of just how catastrophic a high-rise cladding fire could be in 2014, when a cigarette left burning on a balcony sparked a major fire at Melbourne's Lacrosse building.

Adam Dalrymple, from Melbourne's Metropolitan Fire Brigade, said they had never seen anything like it in their 125-year history.

"You have multiple sets of fire over multiple levels all at the same time. What that does is actually challenges the way you fight a fire," he said.

Commander Mark Carter said they now have "enhanced response plans" for six buildings which remain occupied but are considered high risk due to their cladding.

This means extra fire trucks and extra ladders would all need to be called in if fire breaks out in those buildings.

"The reality of fighting a fire in any of these high-rises is … it's an intense resource activity and it's an activity that this has added a huge complexity, the fact that we've got combustible stuff on the facade of these buildings," Commander Carter said.

In the wake of the Grenfell fire, most states began audits to identify which buildings had flammable cladding.

There are now calls to follow the lead of countries like the United Arab Emirates, which has banned the import of polyethylene cladding following several horrific high-rise fires involving the material.

Watch Four Corners' report on flammable cladding on ABC iview.

Editor’s note (11/10/17): The ABC is aware of just one building at Jackson’s Landing that may have PE core cladding – The Distillery Hill building.