With two-bedroom apartments selling for seven-figure sums, it's hard to imagine high density suburbs like Sydney's Waterloo descending into migrant ghettos.
But it's exactly the exclusive nature of such areas that can pose a problem, argue two globally renowned architects. By lumping people of lesser means in far off suburbs with little access to work and limited social opportunities, we must expect it to end in trouble, says French Pritzker Award winner Jean Nouvel.
One solution, argues Italian sustainable cities expert Mario Cucinella, could be laws forcing developers to dedicate as much as 20 per cent of new apartment developments to social housing. That's what his hometown of Bologna has done successfully.
But whatever solution is chosen, it is crucial for Australia to embrace it now as it embarks on policies that will determine how the country settles and accommodates an extra 6 million people, boosting the population to 30 million by 2031. The majority of this increase will be in Australia's cities.
It's something a country like France has failed to manage well, says Jean Nouvel, the country's highest-profile architect, who spoke with AFR Weekend while in Australia this month ahead of the launch of a new apartment tower in Melbourne's CBD.
"Ninety per cent of the terrorists in France are French people living in the suburbs," he says. "And they didn't like, of course, the conditions where they live, because there was very strong segregation and they hate the society for this reason".
Not everyone agrees that the marginalisation of Arab and black immigrant communities into concrete apartment blocks in dense suburbs, known as banlieues, on the outskirts of Paris causes terrorist radicalisation. The majority of French Muslims going to Syria were middle-class, the New Yorker pointed out last year. And even Nouvel says that physical environment doesn't explain by itself why a person grows into a hate-filled extremist.
But equally, there's a problem that political leaders don't acknowledge that there is a link, Nouvel says.
"We refuse to say we could be a little bit responsible for that."
Australian cities are changing in shape as planners approve high-rise dwellings in far greater numbers than ever before. The City of Sydney this week warned state government plans to build a precinct of tall towers in Waterloo on the city's southern edge could give the area a Hong Kong-scale density of around 70,000 people per square kilometre. NSW government developer UrbanGrowth puts the density of the 19-hectare precinct at 873 people per hectare, less than Central Park's 1347 and Darling Square's 1517 people per hectare.
Density is good, as it makes cities compact and the provision of transport and other infrastructure cheaper and more sustainable. But policy makers need to avoid the mistakes of Europe's past, Cucinella says.
"The key point of high density is the social mix," he says. "A city is like an ecosystem – you cannot imagine an ecosystem made only of one species."
It's easier for cities to design social diversity in from the start than it is to retrofit it once problems occur.
Europe, at least, is now trying learn from its mistakes of the past, says Mario Cucinella, an Italian expert in sustainable cities, visiting Australia as part of the Biennale of Sydney. Cities like Paris and Brussels responded to the large numbers of migrants that came to them in the 1970s and '80s by effectively creating ghettos for them.
"We pushed the cities outwards with motorways and built housing," he says. "We pushed poorer people outside the city centre. We only provided buildings. But cities and housing are not only hard infrastructure. They are where people live. They need facilities like schools, libraries, museums and places to dance."
Now Cucinella's hometown of Bologna has reversed earlier policies by mandating that 20 per cent of apartments were for social housing in all new private developments.
"That model is working very well," Cucinella says. "You don't have a ghetto of low-income people and it also prevents poor-quality social housing – if the social housing looks bad developers cannot sell the luxury apartments next to them!"
There are no uniform rules around so-called inclusionary zoning in Australia. SA requires 15 per cent of homes in developments above a certain threshold to be affordable housing. Victoria will pilot it as part of an overhaul of its Plan Melbourne planning blueprint and a government spokeswoman says Melbourne will "eventually" have it across the city. NSW has no such affordable housing policy but is including affordable housing in its Central to Everleigh urban transformation project.
Density in Australian cities, where high-rise towers are found in more affluent areas – the CBDs and inner ring suburbs – is developing differently from Europe, where the concrete towers are on the periphery, or in Asia, where they are throughout the cities. But that doesn't mean Australia is free of social inequality.
"It's just applied in a somewhat different way," says Michael Buxton, a planning professor at Melbourne's RMIT University. "We're dividing our cities on spatial and social grounds. We're clustering people on the basis of income, employment, education and other social criteria in very different social locations. They have very unequal access to the benefits of a city."
That growing inequality was made clear in the federal government's own State of Australian Cities 2014–2015 report, which warned of a widening split between access to employment and other opportunities based on house price and location.
The consequences of bad planning can be extreme. Syrian architect Marwa Al Sabouni last month published a book in which she argues that a lack of shared spaces and sectarian ghettoes created by Syria's government in its cities – in contrast to the country's tolerant past in which church and mosque coexisted peacefully – were a fundamental reason for the country's social breakdown and descent into civil war. She says the problem is repeating itself even now in cities like Al Sabouni's hometown of Homs where the government, as it secures territory it has taken from insurgents, is rebuilding Christian areas but not Sunni ones, The Guardian reports.
While Australia's urban problems are less extreme than those of suburbs like the Molenbeek in Brussels or the peripheral banlieues in Paris, leaders must make decisions now to ensure such problems don't arise, Cucinella says.
"The consequence of bad planning, the consequence of divided classes only becomes clear 20 years later, 50 years later, when it's very difficult to solve because you have already built the environment."
And if cities are built to be dysfunctional, they will become dysfunctional, Nouvel says.
"We cannot be surprised by what happened after."
