Green roofs can make city so cool

Escaping to the soothing surrounds of nature is becoming a rare treat for hard-pressed city dwellers. Ironically, Hong Kong's concrete jungle makes it possible to return to nature. Green roofs on the city's skyscrapers are sprouting in increasing numbers as environmental concerns take root.

'A green roof is a vegetated layer that is installed on a waterproofed and structurally approved roof surface of a building,' says Marcus Swetnam, landscape and design director of Greenroof Asia.

'All buildings can benefit from green roofs. The trials we have done for government involve 'extensive green roofs'. These are lightweight lawns or sedum mats that are grown offsite in one of our nurseries and then moved, by the roll, to the rooftop. They are used for purely economic and environmental benefits - they are not designed to be used as conventional gardens with people walking on them. This is the most economical type of green roof.'

Green roofs reduce the heat-island effect by lowering the amount of heat absorbed by a building and released into the environment.

'Research carried out in Japan and the United States showed that the introduction of green roofs into a city makes a difference to the overall temperature of that city and has considerable economic benefits too. In Hong Kong, a green roof will dramatically cut down air conditioning bills,' Swetnam says.

Green roofs help to improve air quality as photosynthesis by plants absorbs carbon dioxide and releases oxygen.

They can also filter and slow storm water run-off, assisting in the prevention of urban flooding, while also removing pollutants before the water re-enters natural streams and oceans.