Green roofs are receiving praise for not only reclaiming green space in our dense cities but also for their environmental value.
Beyond aesthetics, it is well documented that green roofs can:
- Help reduce the urban heat island effect
- Reduce noise pollution
- Sequester carbon
- Be used as a passive tool for energy savings
- Encourage biodiversity and
- Support biophilia – the connection between human beings and nature
Green roofs (and green walls) are a logical way forward to see nature return to cities.
Despite the mounting benefits, however, green roofs are still perceived as being "too high maintenance," which limits their uptake. We also know very well that a lush landscape rendering of a green roof will only look that way with the correct design from the onset and a working maintenance plan.
Jock Gammon, founder of Junglefy, says there are four things that will instantly reduce green roof maintenance:
People often fail to realise that a green roof can do more than improve aesthetics or aid with climate cooling. It can grow food, help manage stormwater and serve as a city retreat.
Gammon believes the market is maturing, with people installing living infrastructure for more reasons than “it’s the right thing to do.” While green roofs haven't taken off like their green wall counterparts, they are becoming increasingly popular atop multi-story residential apartments, providing amenity spaces for inhabitants of the building.
However, this can usually lead to a space featuring more hard surfaces, including bench seating, decking or pergolas, which is not really a green roof according to Gammon.
For full value to the person and the planet, he suggests extensive green roofs – a substrate of less than 200 millimetres deep – to ensure biodiversity and minimal maintenance.
This also allows green roofs to be used to grow food, creating a “community garden” effect where fresh fruit, vegetables and herbs are accessible by people using the space.
The focus on biophilia has also seen many commercial offices and healthcare spaces explore the potential of a green roof.
“Incorrect plant selection is key to ongoing maintenance,” Gammon said. “If you’re using the green roof to grow food, then it’s going to be higher maintenance.”
In Australia, Gammon encourages people to go with indigenous plant species and natural looking plants.
Learning from the roof growth strategies from Junglefy, he also suggests mixing plant species in order to colonise the green roof and allow nature to take its course.
“This will then lead to better biodiversity and lower maintenance," he said. “For example if you mix a range of species then some will act as colonisers and help other plants that are slower to establish succeed. Over time, different species may dominate the roof, thereby creating an always changing and interesting green roof.”
Gammon also encourages Australia to look to global examples, such as Germany, where green roofs are left to naturally evolve but may not look like a "textbook" garden.
“I think some Australians have a somewhat unrealistic expectation of what these roofs should look like and I guess that comes back to, why are you installing a green roof?” he said.
Gammon offers a formula for maximising the quality of soil substrate.
"Our philosophy is 70 per cent mineral base, and then 30 per cent is comprised of stable organics and less stable organics," he noted.
"Stable organics are things like coconut fibre, that take at least seven to 10 years to break down. Less stable organics such as composted pine barks can break down in three to five years, and the mineral component will always remain there, so that doesn’t break down and that’s the key for a green roof - very high inorganic content.
This in turn can lead to a very shallow substrate, irrigation issues and poor performing plants.
In cities, most green roofs sit above a few storeys, which has led to one of the biggest maintenance concerns according to Gammon – leakage.
He said some people feel putting a garden on top of waterproofing membrane is a bad idea. This misconception that all green roofs are going to leak has also been fuelled by the lack of adequate waterproofing standards currently in Australia.
"I understand you have to go and do a course to get a licence to install waterproofing in a person’s bathroom or kitchen but you don’t actually have to get a waterproofing licence to install waterproofing on a commercial project, which is just ludicrous,” he said.
Junglefy unfortunately experienced this first-hand on one of their projects, where a contractor and supplier misrepresented their expertise. This resulted in multiple leaks on a green roof project.
Gammon also said to be mindful of DIY work, as it’s imperative to get the waterproofing right.
"Once you get it right, the green roof will actually double the life of the waterproofing material as it is protected from UV and the chemical damage,” he said.
As for maintenance, there are a few key tips to keep in mind. The Growing Green Guide, Australia’s first guide to green roofs and walls has outlined five maintenance requirements of a green roof:
- Establishment maintenance occurs during the first one to two years after installation and is undertaken to fully realise the design intent and outcomes.
- Routine or recurrent maintenance includes regular works that are undertaken to ensure the roof is maintained to a minimum or required standard of appearance, functionality and safety.
- Cyclic maintenance consists of scheduled interventions less frequent intervals that maintain infrastructure.
- Reactive and preventative maintenance is undertaken when some component of the system fails suddenly, or shows signs of imminent failure.
- Renovation maintenance includes works that change the design intent.
When looking to hire a professional to build a green roof, Gammon suggests signing a contract that includes ongoing maintenance.
“I think it’s important that the client who is making this investment knows that if something was to happen due to poor maintenance – they are covered," he said. "There is no need for a client to hand more money out – it’s not the way it needs to go.”
If a green roof owner opts to maintain the amenity themselves, Gammon encourages automated irrigation, adding that good access to the roof space should also be a consideration.
“With many roofs on taller buildings, there’s no lift that goes up there,” he said. "You will usually get the lift up one or two floors below and then there’s a ladder that goes up. However, when you’re taking tools and a lot of green waste, it can be difficult.
“So it’s not a determining factor but can come in the very early design stage.”
Solar panels meet green vegetation
The City of Melbourne recently unveiled the City of Melbourne's Rooftop Project, which has mapped out 880 hectares of roof potential (solar, cool or green roofs) in the city. While all three are good options, a combination could prove even more beneficial.
Gammon certainly sees this as an opportunity for performance improvement, though he warned that like all things, maintenance will still be required.
“Solar panels need to be cleaned and they’ve got plants growing around them along with pathways so that presents its own challenges there,” he said. “Instead, you could perhaps have a grid walk mesh, so an open aluminium mesh that could sit across the whole top and the green roof actually grows underneath that.”
This will then still allow access to the space, because a combination of green roof and solar could cause thermal breaches.
Gammon believes there is a lot of growth potential for green roofs.
“I think it’s a very exciting time in the industry," he said. “Two years ago people still weren’t sure whether green roofs or green walls were around to stay but certainly what we’re seeing now is an industry that has assured itself.
“Advances in technology are giving people the confidence that green roofs and green walls can work in Australia.”
He would also like to highlight that all living infrastructure should serve a purpose, whether it’s aesthetic, cleaning water or cleaning air.
“I don’t think we have worked out what the full extent of a plant’s capabilities are but that’s certainly what we’re working on and researching at the moment. It is really how we can make plants a bigger part of our lives and work with us more,” he said.