Living roof project could provide green shoots for Auckland's concrete jungle

RNZ News

30-04-2025

Photo:
Supplied / Auckland Council
A project to measure the benefits of living roofs in Auckland has shown surprising results that researchers hope take root.
The trial led by Auckland University, Ngāti Whātua Ōrākei and local council compared the performance of green rooftops to conventional ones in dealing with the elements.
Those working on the Living Roof Monitoring project atop of Auckland's Central Library say the benefits could be wide ranging.
One of the most impressive findings has been the influence living roofs could have on stormwater management.
University of Auckland professor Asaad Shamseldin, who leads the research with Dr Kilisimasi Latu and Dr Conrad Zorn, said the results have been fascinating.
"They show that the living roof can, for a small rain, they could effectively absorb all the rainfall and even during heavy downpours, they could reduce or they could absorb 80 percent of the rainfall," he said.
"But that's not the whole story, they do have also other benefits in terms of air quality, and also in terms of mitigating urban heat islands."
Photo:
Supplied / Auckland Council
An urban heat island happens when a city experiences much warmer temperatures than nearby rural areas due to the concentration of buildings and human activity.
"So the research we are doing so far shows that during the summer, when it's very hot, the living roof is acting like a natural air conditioner, and when it is very hot, then the green roof will reduce the temperature, anything between 32 to 56 percent, and not only that one, it also delays the peak."
"It's providing cooling to the roof and of course if you have a cooler building, it means that if you are using air conditioning and stuff like that, it means that you don't need to use a lot of energy to cool your building.
"Also the wind blowing from the sea plays a considerable part in the cooling and also delaying the peak and during the night the wind helps to narrow the gap between the temperature in the living roof and the conventional roof," Shamseldin said.
It's all down to the more than 2000 native plants on the Auckland Library roof which were propagated by Ngāti Whātua Ōrākei in their nursery and planted five years ago.
"Kaupapa like this green roof are examples of cultural infrastructure, they integrate nature into our cities and allow us to actively elevate the mauri of our taiao," said Etienne Neho of Ngāti Whātua Ōrākei.
"It was a way to also showcase to the rest of Tāmaki that having a green roof on your building has so many benefits, more than just bringing back the birds, It helps with the rainfall, It helps with basically the maintenance nightmares that some buildings can face with having a lot of high water on their roofs.
"But also it shows that there's a way that we can offset our development in our buildings through having some form of green within our building scapes.
"We looked at plants that traditionally would have been found in waterways and would have been found in swamps and in areas where there was a lot of high water.
Photo:
Supplied / Auckland Council
"So we've got our rushes and our reeds in the form of oioi, they're a plant that you'd find quite commonly along the banks of awa and stream, they're water filterers and they're water holders.
"They're really soluble to the water, so when it's raining and when, say for example, you have a bit of surface flooding, they'd soak them up and they'd hold that as well as re-releasing it in a filtration system.
"It was a choice of what plants not so much looked good, but what plants would be well suited for their purpose up here," he said.
Neho, who manages the Ngāti Whātua Pourewa Maara kai, said it was fitting the pilot programme that they were hoping to learn from, was conducted on the roof of a library.
The actual design and the layout of the plants is in a whareki format, which is a form of weaving, and the actual design itself is called poutama.
"Poutama, to those that know, means growth and ascension, and it's fitting that it's on the library rooftop because as the people grow down below via their book work and via their studies, the plants are growing on top, and they're kind of teaching us as well how they can thrive in this setting.
"Despite the odds, on a rooftop in sometimes quite harsh conditions, they can thrive as well, and that's a learning for us as well," he said.
The plants have been thriving, with a 90 percent survival rate according to Auckland Council's curator botanic gardens Bec Stanley.
"The aim for this roof is that it's self-sustaining, so in the early years of any green infrastructure, you do need to manage them a little bit more while they're establishing.
"But through time, it's expected that they become self-sustaining and we're already seeing that here.
"We're seeing the plants we've planted, but we're also seeing their progeny, we're seeing their offspring, these plants are flowering, they're seeding, and their seeds are germinating and growing new plants," she said.
And where there's native plants, native animals are soon to follow.
"We've seen a few insects arriving on the roof and the more flowering that we see, the more pollinators will be attracted to this roof.
"So especially I'm interested in the harakeke, the tui, for example, in the inner city, I'm thinking that they will eventually find this roof because harakeke are a really, really enticing food source for them.
"We're particularly hoping we get some native insects here to pollinate our native plants, and also some pollinators like birds.
"Increasingly we're hoping to get more native animals up onto this roof to live in association with the native plants that we've planted for them, that's the goal," Stanley said.