Could Green Roofs Offer a Solution to Urban Environmental Challenges?

Sourced from the Irish Examiner

Could green roofs offer a solution to the challenges urban environments face, asks Peter Dowdal

IT’S a buzzword in many urban planning circles around the world but what does the term “green infrastructure” actually mean? Green infrastructure provides the ingredients for dealing with environmental challenges by building with nature. If you look at the environmental challenges facing most urban areas at the moment, they include: urban heat, biodiversity loss, storm-water flooding, noise pollution, poor air quality, and lack of green amenity spaces.

The good news is, as always, that nature and the garden offers a solution to nearly all these problems. If only we would stop discounting the green environment and looking upon it as something to be controlled and concreted over and instead work with it then we would be far more successful in our endeavours. Green roofs not only counteract the challenges listed above, they actually have proven positive results in relation to all of them.

A green roof is simply a roof which is planted. They can be broken down into three categories: extensive, semi-extensive and intensive. An extensive green roof can be created on the smallest of spaces, even on the roof of a garden shed. Needing only 5cm-15cm of growing medium, they are typically self-sustaining, needing little or no watering or weeding, and are available in ready-grown mats which can simply be laid out.

There are layers to be included before any green roof can be installed such as waterproofing, insulation, weed barrier and drainage. Planning permission and engineers reports may be necessary for larger projects so it is important that you use a contractor who knows about green-roof technology.

Semi-extensive green roofs require a slightly deeper layer of growing medium, about 10cm-20cm to sustain perennials but not trees and shrubs and, finally, intensive green roofs need at least 30cm of growing medium which needs to be organic matter and will thus require a much stronger structure.

Could the hare’s-foot clover, Trifolium arvense, solve Cork city’s flooding problem? Dusty Gedge, a member of the Building a Green Infrastructure for Europe committee and a world leader in green-roof design and installation, has been promoting the use of green roofs as a mainstream building covering for over 20 years. This Trifolium is his favourite plant to use in green roofs for its aesthetic value as much as anything else.

Dusty has found that conditions on roofs are similar to those of coastal areas. Rooftops are, of course, very windy and whilst they may not have to contend with salt, they do have pollutants in the air and thus plants which do well on the coast such as alpines, and low-growing plants like the Trifolium and also Saxifraga, Sedum, Armeria and some grasses, thrive in these conditions.

In the City of London there is now 5.8m of green roof per person. Brownfield sites too, meaning disused industrial sites, are also rich in biodiversity. Battersea power station in London contains seven protected species and will be the biggest green-roof project in London in 10 years’ time.

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