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The benefits of green roofs

Jardin Atlantique, a park and garden located on the roof of the Gare Montparnasse railway station in Paris. Photo: Antoine Gatt

Jardin Atlantique, a park and garden located on the roof of the Gare Montparnasse railway station in Paris. Photo: Antoine Gatt

A University of Malta faculty is currently studying the feasibility of green roofs in the Mediterranean region. Assistant project director Vince Lloyd Morris outlines the various advantages of this technology, including energy savings and the filtering of airborne pollutants.

The LifeMedGreenRoof Project, recently set up within the Faculty for the Built Environment of the University of Malta, is an innovative project that looks at the feasibility of green roofs in the Mediterranean region, particularly in Malta.

Although green roof technology is well established in many countries, there is very little information on green roof performance in countries with a Mediterranean climate. The project is therefore breaking new ground.

In a nutshell, a green roof consists of a layer of ‘soil’ or growing medium spread over a roof surface or a significant percentage of it. This layer is then planted with vegetation. The intention is to use native plants on green roofs in Malta as they are obviously adapted to the islands’ climate, are hosts to native wildlife and are also attractive in their own right.

So how could installing a green roof be of benefit? First of all, the deep layer of growing medium acts like an insulating ‘blanket’, keeping living space beneath warmer in winter and cooler in summer. A recent study by the City of Chicago comparing conventional and green roofs found daytime differences in August roof temperatures of 28˚C.

A green roof would thus save energy costs involved in heating and cooling. How effective the insulation would be in a Mediterranean climate is a question that the LifeMedGreenRoof Project is hoping to evaluate.

Additionally, the reduction in the use of both heaters and air-conditioning units would mean a reduction in carbon emissions, thereby mitigating global warming. Malta is committed to reducing carbon emissions by 10 per cent by 2020 via its National Energy Efficiency Plan (NEEAP). There is, therefore, some urgency to do everything possible to reduce the energy requirement of buildings in Malta.

In the 1970s scientists began to describe the effect of cities becoming significantly warmer than the surrounding countryside as the ‘urban heat island phenomenon’ (UHIP). This is caused by concrete, masonry and tarmac absorbing and storing heat from the sun during the day and releasing it at night. This means that air-conditioners are used more frequently and intensely.

This phenomenon is locally of concern due to high building densities and the destruction of many gardens and other green spaces which generally counteract the effects of UHIP. Scientists have predicted that if five per cent of the roofs in a built-up area were to be vegetated, the UHIP at midday in June could be reduced by between 1 and 2˚C. So a fairly modest adoption of green roofs could have real benefits in terms of improving comfort and saving energy.

The deep layer of growing medium acts like an insulating ‘blanket’

At first it might seem that the installation of photovoltaic cells and green roofs may prove to be at odds with each other. Research in other countries has shown that installing a green roof beneath photovoltaic panels actually increases their efficiency. The reason for this is that above about 25˚C the efficiency of the panels decreases. The reduction in ambient temperature by green roofs means that photovoltaic panels in hot climates remain more efficient for longer.

So it can be seen that the installation of green roofs in Malta has the potential to result in significant energy savings. But apart from such advantages, the installation of green roofs can bring other benefits that have the potential of improving the quality of life of urban dwellers.

Green roofs can reduce noise and filter airborne pollutants, a cause of ill-health, especially respiratory-related diseases. They create habitat for wildlife and pleasant places for people to relax and entertain. They can increase the aesthetic attractiveness and subsequent property value and increase economic activity and ‘green’ jobs.

In addition, the ability of green roofs to absorb rain – they act like a sponge – and release it slowly would reduce the risk of urban flooding and thereby reduce the financial and human costs caused by flood damage.

One of the main objectives of the LifeMedGreenRoof Project is to set up a demonstration green roof on one of the buildings at the University of Malta. It is hoped that professionals involved in construction and planning development in Malta, as well as the public, will be able to visit the garden and see for themselves the benefits of installing green roofs in Malta.

The demonstration garden is scheduled to open early next summer. Meanwhile, tests are currently being carried out to confirm the performance of the growing media and plants.

If you would like to keep in touch with the development of the LifeMedGreenRoof Project, visit the project website at www.lifemedgreenroof.org or visit the project’s Facebook page.

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