The Review 2007

24 25 Professor Jim Chi-yung on the roof of the Runme Shaw Building From Barren Rooftops to Green Oases Hong Kong’s barren rooftops can get surprisingly hot in summer – as high as 54 degrees Celsius when the maxi- mum air temperature is about 32 degrees Celsius. But new research is showing that greening rooftops can solve this problem. The green rooftop concept had never been properly tested in a climate like Hong Kong’s until mid-2006, when Chair Professor of Geography Jim Chi-yung began experi- menting with green roofs on the top of the Runme Shaw Building and found significant impacts. A 10-centimetre layer of waterproofing, water storage, drainage, soil and vegetation was able to reduce rooftop temperature fluctuations to no more than 4 degrees Celsius on a summer day. That in turn can notably reduce tempera- tures in top-floor apartments. Professor Jim tested grass, flowering herbs and shrubs and, while shrubs performed best, they all demon- strated a significant cooling effect on bare roofs. “Living vegetation can absorb a lot of heat, which helps to reduce electricity consumption and lower the heat-island effect in urban areas, and it also absorbs gaseous pollutants and dust particles. On top of that, green roofs can be a very attractive amenity and recreational space,” he said. The modern green roofs are relatively lightweight so there were no load-bearing problems. With the excep- tion of shrubs, they can also be walked on and used for other purposes. The next step will be to test different drought-toler- ant plant species to see whether they can survive the ex- tended dry spells of Hong Kong’s autumn and winter and minimise maintenance input. Professor Jim will also meas- ure changes in the quality and quantity of rainwater released from green roofs. Living vegetation can absorb a lot of heat, which helps to reduce electricity consumption and lower the heat-island effect in urban areas.