Green roofs to cool you in the heat of global warming

A green roof covered by flowers or grass has a strong vibe of flower power. The biggest ecological benefit of a green roof lies in its cooling effect.

Green roofs to cool you in the heat of global warming

– The growth platform and the biomass bonded to it act as an insulation layer. The plants cast a shadow, and they also have a cooling effect through transpiration, explained Professor Brad Rowe, horticulture specialist from the Michigan State University, when lecturing at the University of Helsinki's international green roof seminar on Monday, 18 April.

According to Rowe's research, a green roof is 167 per cent more effective than a traditional roof in preventing heat transfer to indoor spaces. This will save a lot of money and fuel.

On a global scale, more energy is used for cooling than for heating – and as global warming progresses, the need for cooling will also increase in Finland.

Flowers for people and butterflies

Despite the benefits, Finland still has a long way to go in the utilisation of green roofs. Jouko Hannonen from the Finnish Garden Association laments the slow start.

– It is the nature of an engineer never to admit their ignorance. They don't know the proper parameters for the green roof structures and build them too heavy just to be on the safe side. This is expensive. Fire safety authorities may also say no to a project just because they are uncertain, Hannonen said.

Professor Nigel Dunnett from the Department of Landscape at the University of Sheffield emphasised that although benefits are obvious, green roofs need to achieve social acceptance first.

– We must create green roofs of dramatic beauty which people will think are fantastic. This is where aesthetics and biodiversity meet: insects love pretty flowers, just like people do, Dunnett said.

Visitors photographing ugly roofs

International top researchers of the field recommended that the thickness of the growth platform should vary even on the same roof, as different plants favour different growing medium.

– If you throw seeds of 50 different plants on an even roof, you will not get a green roof with 50 kinds of plants, said Professor Stephan Brenneisen from the Zurich University of Applied Sciences.

There are hardly any green roofs in Helsinki, which was observed by the visitors. Dunnett and Professor Mafred Köhler from the Neubrandenburg University of Applied Sciences amused their audiences by showing pictures of ugly bare roofs, taken through the hotel window and on the streets. Buildings such as the Kluuvi shopping centre, Porthania, Central Railway Station and Kiasma Museum of Contemporary Art all received sharp critiques.

At the University of Helsinki, green roofs are studied within the Fifth Dimension research project jointly carried out by the Finnish Museum of Natural History and the Urban Ecology Research Group. The project is a part of the university's World Design Capital Helsinki 2012 programme.

HENVI Science Days 2012: International Scientific Meeting for Green Roof Research »»

Fifth Dimension – The Green Roofs in Urban Areas project »»

University of Helsinki blog on World Design Capital Helsinki 2012 »»

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Text: Antti Kivimäki
Photo: Niina Ala-Fossi
Translation: AAC Global
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