Raising the (green) roof

In the wake of World Green Roof Day on 6 June, a studio visit to the burgeoning Melbourne SkyFarm sparked Senior Associates Erwin Taal and Warwick Savvas (who contributed to the Growing Green Guide: A Guide to Green Roofs, Walls and Facades in Melbourne and Victoria, Australia) to examine the growth of green roofs in an Australian context.

When done well they are lightweight, cost effective, low maintenance, and provide many benefits that can be measured and quantified.

By covering a structure with a living extension of the landscape, we can make a meaningful contribution to a more resilient, biodiverse world, particularly in constrained urban areas where space is precious.

They look pretty good, too.

More green roofs would be, in our opinion, a win. But we do need to be careful. As with many other recent sustainable trends and requirements, the spectre of greenwashing looms. A considered assessment and the use of the right approaches and systems is crucial, with consideration lavished on the sourcing of materials, embodied carbon, the use of appropriate plant species, maintenance and monitoring, and end-of-life reuse and recyclability.

Over the past decade, ASPECT Studios in Melbourne has developed green roofs in a wide range of sizes and locations. These range from the 27,000m2 roof that blends the hulk of the Victorian Desalination Plant into its sensitive coastal landscape, to the smaller 270m2 roof at Tarrawarra Abbey, which conceals a sophisticated irrigation system that can be used to form a shield against bushfires.

As a result, we are keenly aware of just how substantial the positive impact of green roofs on the environment and surrounding communities can be. For example:

• Green roofs improve the thermal performance of buildings and reduce energy costs for heating and cooling: when located with solar panels they help cool the panels on hot days, which improves their performance. 
• Green roofs reduce storm water runoff by absorbing rainwater and filtering it through the soil, which slows down the rate of flow and allows it to seep into the ground naturally.
• Green roofs provide safe habitats for birds and other wildlife.
• Green roofs minimise the Urban Heat Island effect by cooling the surrounding air temperature, which can have a significant impact on the overall climate of a city.
• As a visually pleasing natural element, green roofs can promote wellbeing through biophilia.

But where green roofs have been widely implemented in certain cities across Europe, Asia and North America, they have been slower to catch on in Australia. This can be explained in a number of ways: the structural requirements for a successful green roof are more complex and therefore more costly, there are (usually unfounded) perceptions of risk around drainage and leaks, and a scarcity of information that demonstrates the benefits in concrete terms.

The Australian Institute of Landscape Architects (AILA), as a key member of the Living Cities Alliance, advocates for the development of a green infrastructure policy framework to support increased green roof implementation. View the Green Infrastructure Position Statement here.

And with the new initiative developed by the City of Melbourne to help in the response to the climate and biodiversity emergency, a key opportunity to do so has emerged. Through changes to the Planning Scheme Amendment C376, developers will soon be required to achieve a minimum score derived through the City of Melbourne’s Green Factor tool.

The Green Factor Tool was created in 2019 to gauge how the planned and current green infrastructure at the building level can affect the city's objectives for controlling urban heat, boosting biodiversity, mitigating stormwater runoff, increasing social amenity, urban food production and the overall aesthetics of the built environment. Numerous councils across Victoria have since voluntarily adopted this tool, which aims to improve urban greenery and enhance the character of new developments by integrating green infrastructure components into their outcome.