So tell me a little more about these
Another key benefit to green roofs is that they mitigate the urban heat island effect. A chapter study by the United States Environmental Protection Agency (EPA) reported that green roofs were substantially cooler than their dark or white counterparts.
Comparing two roofs in Chicago, the study found that on a 32 degrees Celsius (90 Fahrenheit) day in August, the green roof temperature ranged from 33 to 48 degrees Celsius (91 to 119 Fahrenheit) while an adjacent dark conventional roof dark temperature was 76 degrees Celsius (169 Fahrenheit).
“The near-surface air temperature above the green roof was about four degrees Celsius (seven Fahrenheit) cooler than of the conventional roof,” the report read.
A similar study in Florida found that the average maximum surface temperature of a green roof was 30 degrees Celsius (86 Fahrenheit), while the adjacent light-colored roof was 57 degrees Celsius (134 Fahrenheit).
Green roofs have also been shown to have healing properties. Humans love greenery and research demonstrates that the presence of plants can directly contribute to health and well-being. Healing gardens in healthcare spaces help patients to recover more rapidly, while office workers become more productive when working around living plants or enjoying a green view.
The roofs also offer a green community to cities and building inhabitants. There is nothing quite like retreating to a lush canopy sky garden atop a skyscraper or visiting a roof terrace during office hours to escape from the glare of digital technology..
It is recommended to use plants native to the region – it’s their best chance of survival.
For example, the recently opened Sky Garden in London atop 20 Fenchurch Street (the Walkie Talkie building) has utilized drought resistant Mediterranean and South African species.
According to Sky Garden’s website, it is London’s tallest green roof and is housed beneath a canopy. However, the plants have been specifically chosen to work in harmony with the particular quality of light found under the canopy so flowers can flourish all year round.
It is also encouraged for architects to look at building materials when selecting plants.
If we look at our cities, the building materials that we use for all the multi-story buildings is a refined geology: rocks, glass, steel and all kinds of concrete. They’re like a raw mountain which can struggle to grow plants and unfortunately people look to just keep putting substrate on top of it that will retain water and grow plants that need a lot of water. Why? Because it looks good.
Air plants in particular can go on buildings with little maintenance. They’re particularly good for seriously high buildings as they can be installed at the development stage.
There is also an issue related to soft vs. hard tissue plants.
“If a soft tissue plant falls of a building, it’s not going to kill anyone,” comments Ecological artist Lloyd Godman. “It is similar to a leaf coming down a building.”
Hard tissue plants on the other hand are bits of wood, branches etc. Should you have a tree on rooftop and amid a storm with 100 kilometer winds a branch breaks off, it will not float like a leaf, it will go directly over the edge of a building and hit whatever is below.
Maintenance, unfortunately, is not generally discussed beyond the measurable substrate, beautiful flora or irrigation system. The fact is, green roofs require maintenance – a lot of it.
The recently completed One Central Park building in Sydney has six full time gardeners something Goodman said is necessary.
“It costs approximately 20 to 30 per cent of your installation cost to maintain a green roof or vertical garden,” Godman said, noting that many are decommissioned because maintenance costs are too high or plant selection wasn’t deeply considered.
“This isn’t a problem,” he said. “We just need to be honest about it and know that plants have a limited life, they do need maintenance. I don’t like the term ‘self-sustaining. I just don’t see it that way.”
From an economic point of view, this does show promise for the landscape employment sector and rising opportunities for garden maintenance jobs.
So are green roofs the future? Well in Godman’s opinion, “This is the only way we are going to cool this planet down.” Here are a few of Godman’s predictions:
- Buildings without plants on them are eventually going to look old fashioned – buildings need to become an extension of our parks.
- City councils will bring in bylaws like they did with insulation where builders will have to cover a certain percentage of a building’s surface – roof or facade – in plants.