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As if the implications of the unfolding global financial crisis weren’t bad enough, the Irish economy must also contend with the consequences of a banking system exposed to unprecedented property-related debts. Reflecting on the ongoing crisis, Richard Douthwaite explains why investment in local energy innovation may prove the key to improving Ireland’s economic health
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Page 2 of 6
The moos filtration plant near Zurich in Switzerland features nine acres of extensive roof meadow that supports 175 different plant species, including rare green-winged orchids
The basic components of most green roofs are the same: a frame to hold
the soil in place (often made of timber), a waterproof membrane, root
barrier layer, drainage zone, growing substrate, and vegetation.
Some modern examples of green roofs are striking. The Acros building in
Japan’s Fukuoka city features a series of terraced green roofs that
reach 60 metres in height, merging seamlessly with an adjacent park at
ground level, while Ford’s River Rouge factory complex in Michigan
boasts ten acres of ‘living’ roof - the world’s largest - designed by
noted green architect William McDonough.
But green roofs are more than an architectural statement designed to green the grey urban environment. They offer impressive practical benefits too, such as drastically reduced rainwater runoff, increased urban biodiversity and impressive insulation performance. They also provide green space in dense urban areas, and help to cool local temperatures. “They tick all the boxes,” Mairead Stack says.
As global temperatures rise, green roofs can play a key role in mitigating the effects of climate change in urban areas, where artificial surfaces absorb heat and buildings dominate the skyline, raising local temperatures above those in the surrounding countryside (the urban heat island effect). By evaporating water and absorbing less heat, green roofs reduce local temperatures. The surface temperature of Chicago city hall’s green roof can be as much as 44oc cooler than conventional roofs nearby, while in Toronto researchers concluded that if all possible roof space in the city were greened, it would lead to a 0.5 – 2.0oc reduction in city temperatures.
Greening a roof can affect temperatures within buildings too: a green roof can reduce summer temperatures underneath the roof membrane by 15oc and raise winter temperatures by 2.5oc, according to a study conducted at the University of Nottingham.
From an engineer’s perspective, the ability of green roofs to reduce rainwater runoff is impressive: research carried out in the temperate Pennsylvania climate concluded that an extensive green roof can reduce runoff by up to 100 per cent in summer and 30 per cent in winter.
Green roofs can also neutralise acid rain and sequester carbon. “We’ve tested a typical sedum roof, and the amount of carbon sequestered is small,” Brad Rowe, associate professor of horticulture at Michigan State University told Construct Ireland. “It’s comparable to desert scrub. But if you have something deeper it’ll have more biomass, and it’ll sequester much more. Even with a sedum mat though, it’s more than is sequestered on a typical roof.”
With the principles of sustainable drainage systems (SuDS) - including
the demand that runoff in new developments should not exceed that of a
typical greenfield site - enshrined in the development plans of every
local authority in the greater Dublin area, green roofs could soon
become a common facet of new developments in the city. “The most
practical way of meeting the requirements of SuDS in a high density
area is to use a green roof,” says Don McEntee, senior engineer with
Dublin city council, though he says that permeable paving is another
viable option.
An extensive green roof in Freiburg, Germany features an array of Solar PV cells. Green roofs assist solar PV technology by cooling rooftop temperatures. Overheating is a key reason for inefficiencies in PV technology
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Issue 2, Vol 5 Out Now
The new look issue of Construct Ireland is available now. Click here to subscribe online and have the latest issue delivered to your doorstep
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