Decarbonising our cities


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Cities are a major source of carbon emissions. Our expert panel discussed how we’ll reduce the climate impact of the built environment.

The built environment accounts for 39 per cent of gross annual carbon emissions worldwide.

How do we reduce the impact of our cities on climate change? Our webinar convened a panel of experts, chaired by the City of Melbourne’s Director Greenline, Mark Allan, to discuss.

Watch the webinar

How to account for embodied carbon emissions

Operational emissions – for example from the electricity it takes to heat or cool buildings – account for some built environment emissions.

But embodied carbon emissions also contribute a significant proportion. They are carbon emissions caused by construction as well as the extraction, manufacture and transportation of construction materials.

Replacing an energy-inefficient old building could reduce operational emissions but add to embodied carbon emissions.

And balancing that equation can be challenging, as calculating embodied carbon emissions involves uncertainties. Different databases give different values for embodied carbon coefficients, which represent the amount of carbon emitted per unit of material. But experts can help navigate this uncertainty.

“We all have to commit to transparency in our approaches to embodied carbon calculations. We need to share data sources, and methodologies and assumptions used in our calculations. And only then can we foster trust and comparability so that we can ultimately reduce embodied carbon,” said Dr James Helal, Lecturer in Sustainable Structural Design and Assistant Dean (Sustainability) at the University of Melbourne.

Designing new buildings to minimise carbon emissions

“To reach our net zero emission goals, we must reshape the way we think about buildings. They’re not just shelters. They’re living, breathing entities that should be designed and operated with a clear understanding of their impact on our ecosystem,” said Dr Behzad Rismanchi, Senior Lecturer in the Department of Infrastructure Engineering at the University of Melbourne.

Specifying carbon targets, including embodied carbon, and engaging with engineers or sustainability consultants early is crucial.

“Optimisation [of building designs] can only take us so far,” said Environmental Designer Lucy Marsland from Atelier Ten.

Applying circular economy principles to building design will inherently achieve decarbonisation.

“Circular economy at its heart aims to keep materials in use. This is done through a combination of measures focusing on resource efficiency, designing out waste and extending the life cycle of materials when they’re in use,” said Ian Dixon, National Lead for Building and Property Sustainability at GHD.

To encourage low-carbon solutions even when there’s no immediate payback, Marsland said we must challenge the way we view the built environment – which is as business assets first and foremost.

“Maybe we need to think rather about investment in the community,” she said. Bringing in experts from social sciences, economics and community organisations can help quantify benefits in a more holistic way.

The role of existing buildings in reducing carbon emissions

Retrofitting old buildings rather than building new is an option for some projects and clients, but not all buildings are suitable.

“We’re currently involved in a project to develop guidelines on ‘rebuild vs reuse’ decision-making that happens quite early on in these projects. It is quite complex, though. There’s the ‘triple bottom line’ of the social, financial and environmental [considerations]. On top of that you’ve got risk,” said Dr Helal.

Sustainability also means using resources more efficiently. One building’s waste heat could be another building’s heat source. But in cities, these buildings likely have different owners – which means stronger governance is needed.

“From a technical perspective there are so many opportunities at the city level in terms of sharing resources and sharing energy and so on. But the complexity to be resolved here is the governance and the ownership and the responsibility around that,” said Johanna Trickett. She leads ARUP’s education business.

Register for the Retrofit Symposium to learn more

How universities model sustainable cities

In Australia and New Zealand, 60 universities occupy three times the space of Melbourne’s CBD. Like cities, Trickett said, their buildings include diverse typologies from high-tech laboratories to car parks. And they tend to have aging buildings that are usually fully occupied and thus difficult to retrofit.

“I think a lot of cities and other sectors can learn from the education sector and the universities – like the University of Melbourne – pushing the boundaries on sustainability matters,” said Trickett.

Many universities have set ambitious emission targets. The University of Melbourne has pledged as part of our Sustainability Framework to become carbon neutral by 2025 and climate positive by 2030.

“Universities tend to be the most courageous clients,” Trickett said.

The Retrofit Symposium brings together academic, government and industry experts to set the national research agenda to support the transformation of Australian cities. Register for the Retrofit Symposium.

First published on 28 September 2023.

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