In addition to garnishing otherwise arid, glass and concrete urban environments with edifying nature areas, green roofs also bring a raft of benefits that can significantly enhance the efficiency and sustainability of the modern city.
Joe Glesta, a graduate student researcher at the University of Melbourne, points to the broad range of positive impacts that green roofs can have on urban environments.
“The benefits of green roofs include decreased cooling and heating loads, improved air temperature, improved air quality, reduced urban heat island effects, carbon footprint reduction, improved stormwater management, storm water runoff quality and urban hydrology, as well as sound insulation and attenuation, which is very important in a city,” he said.
“I can tell you that the city of Melbourne is currently interested in green roofs for their effects on urban heat islands, water retention and storm water management, as well as biodiversity, which is another area that isn’t too often considered.”
The ability of green roofs to reduce the urban heat island effects of cities is already well documented, and sure to become an area of increasing focus as addressing the impacts of climate change becomes a more urgent priority.
“Research has substantiated that large and low buildings with green roofs on them have the potential to remedy the heat island effect by offsetting it with evapotranspiration,” said Glesta. “Green roofs are capable of dampening heat in certain areas, and lower the temperatures of buildings or the areas around them. This will be an important feature for cities because of climate change, and the increasing amount of thermal mass that will be retained to the greater number of hot days.”
In addition to their heat-dampening propensity, green roofs can also help cities deal with one of the other major impacts of climate change – the increased frequency of strong rainfall and flooding, by improving storm water management in urban settings.
“A green roof can act like a sponge in many ways, capturing the water and using it to feed plants before slowly releasing it,” said Glesta. “This means they can play an essential role in storm water management, by reducing the total output of storm water as well as the rate at which it flows into drains.
"Without a green roof acting as a sponge, rain water falling in high volume and intensity runs off extremely quickly, overflowing drains, creating severe flooding problems, and costing Melbourne as much as $245
million dollars annually.
“In the city of Melbourne it’s exciting because we have the opportunity to use the green roofs as a sponge on a layer of the urban fabric that is completely underutilized, improving our ability to absorb of water and reduced storm-related damage.”
According to Glesta, the ability of green roofs to improve storm water management is one of its chief appeals for urban planners around the world, leading to their widespread adoption in a number of major cities that are frequently beset by heavy rainfall.
“Berlin, Chicago, Portland and Rotterdam are all using green roofs for storm water management, as are Toronto and New York to a less extent,” said Glesta. “Portland for example has 39 acres of green roofs, which is a monumental amount, as part of their storm water management strategy.”
In addition to helping cities deal with the worsening climate conditions caused by global warming, green roofs can also have a positive impact on urban environments by raising their biodiversity.
“There’s a fair amount of literature showing that biodiversity can be increased via the usage of green space, and green roofs are one of features that can achieve this,” said Glesta. “While there’s still much debate surrounding whether biodiversity can be achieved via green roofs specifically, it has been proven that it’s possible in many scenarios, depending on the specific city and the flora and fauna surrounding it.”
On top of the broader ecological advantages that green roofs can bring to urban environments, they can benefit property developers and owners by adding significant value to the individual properties on which they're installed.
“There's a study indicating that green roofs can increase property values by as much as 9 per cent,” said Glesta. “They are an extremely good way to elongate the life of a roof, as well as showcase concern for the environment and sustainability.”