A resident of the M Central apartment complex, in Pyrmont, sunbakes on the building's green roof. Credit:Wolter Peeters However, they say a lack of proactive policy measures mean this opportunity is slipping through the hands of the NSW government and councils. "In the absence of a proper evidence-based consideration of green space and green infrastructure, we're likely to see the slums of the future being developed," Dr Paul Osmond, director of UNSW's sustainable built environment program, said. "In 10 to 20 years' time, will people want to live in these places?" Scientific research has repeatedly recognised the insulation benefits of living infrastructure, such as green roofs and walls, in reducing energy consumption both in summer and winter, lowering energy and electricity bills as a result.

The One Central Park building, on Broadway, Chippendale, with its eye-catching green facade, has become an iconic feature of Sydney's inner city skyline. Credit:Jessica Hromas For example, a 2015 experiment, conducted at the University of Technology, Sydney, found that the process of retrofitting one of the university's roofs with succulent plants lowered the roof temperature by as much as 5 degrees. A separate study by UNSW professor Mat Santamouris found the large-scale application of green roofs could lower the ambient temperature by up to 3 degrees. Sara Wilkinson, from the UTS school of built environment, said about 32 per cent of horizontal surfaces in Sydney are rooftops, but the potential has remained largely untapped. In the City of Sydney, the only NSW council that has a specific policy on green roofs and walls, there are 53 green roofs, which equates to less than 1 per cent of the total available roof space.

At a policy-level, Sydney lags well behind other more dense cities such as Singapore, London, Stockholm and Toronto when it comes to promoting the installation of green roofs and walls, Dr Wilkinson said. "Greening them really does make a change to heat stress and your urban environment," she said. "We are missing an opportunity to create a beautiful garden city." Singapore, by comparison, is widely recognised as a world leader when it comes to green roofs. As one of the most densely populated countries in the world, it is also an example of the success that can be achieved through a co-ordinated and targeted policy framework. "They realised back in the '60s they were a concrete jungle and they needed to do something about it," Dr Wilkinson said. "What we're seeing in Singapore now in 2018 is 40 years of planning and policy setting."

The uptake of green roofs in Singapore has boomed by more than 800 per cent in the past decade, and today the compact island has 80.5 hectares of skyrise greenery across 182 projects. This has been driven by an array of government-led incentives, such as planning policies that offer developers additional floor space, or grants that cover up to 50 per cent of the cost of green roof and wall installations. No equivalent measures or financial incentives exist in Sydney. However, the NSW government has made recent significant steps into this space, unveiling a draft green infrastructure policy last November, which increases Sydney's urban tree canopy from 16 to 40 per cent through the planting of 5 million trees. At the same time, the government is pushing ahead with planning strategies that concentrate new high rise developments around train stations. For example, rezoning around 11 stations along the Sydenham to Bankstown rail corridor is expected to deliver 35,000 new homes over the next 20 years. In December, the government cleared the way for a further 20,000 homes to be built through rezoning around the rail corridor from Macquarie Fields to Macarthur in Sydney's south-west.

Jock Gammon, co-founder of Junglefy, a company that installs and maintains living infrastructure, said it was more cost effective to install green roofs during the building's construction, and incentivising developers was key. "It won't happen retrospectively because once they [developers] get their certificate, they aren't really going to want to put one up," he said. Aside from the environmental benefits, rooftops are also an obvious, if partial, solution to the increasing encroachment by development on green space at ground level. At the M Central apartment complex in Pyrmont, the 3000 square metres of landscaped rooftop joins the two separate apartment buildings, providing a communal space for residents to mingle and walk their pets. "When we show potential renters into the building, that is really the point of sale. They see the roof and say 'wow'," building manager Karl Rees said.