Green Roofs Create Oases in the City

Knowledge Exchange Video

Green Roofs Create Oases in the City


Green roofs have been in use since early humans first covered basic structures with sods and plants that kept them warm in winter and cool in summer. But these primitive shelters were not waterproof, had no floor coverings and did little to keep out burrowing animals.

Jump thousands of years forward to present day Hong Kong and there are still many perceived limitations - and often societal resistance - in adopting green roof technology in spite of its recognised benefits for today’s power-hungry cities.

As early man discovered, green roofs improve the thermal performance of buildings. This in turn allows buildings to remain cooler in the summer by evaporative cooling and reflecting and dissipating solar radiation, while retaining heat during the winter months. Rainwater can be absorbed by the green roofs to be released gradually to reduce the scale of drainage infrastructure and flooding. They also serve as wildlife oases, providing refuge for wild animals living in the green islands or "stepping stones" for those navigating a way through the concrete jungles that are modern cities.

Professor C Y Jim, Chair Professor of Geography at The University of Hong Kong, is a pioneer in this field and is dedicated to ensuring more buildings in the city have a green covering, including external green walls, containing micro-ecosystems where possible.

Professor Jim has designed and built more than 20 high-rise green roofs in the city, including at HKU, at various schools, and three on Tai Po rail station. His collaboration with CLP Power Hong Kong Limited (CLP) is an exemplary knowledge exchange project - together they have created the largest Sky Woodland in Hong Kong at a CLP substation in Tseung Kwan O, covering two roofs and exterior walls.

"Green buildings can provide us with beautiful scenic views, and they can clean the air, cool the air, cool the city, and they can provide a sort of soothing ambience for people," Professor Jim said.

Monitoring equipment has been installed on the CLP substation to allow a full set of microclimatic data to be collected on the temperature, humidity, solar and terrestrial radiation, wind and rainfall to evaluate thermal, hydrological and ecological benefits of the green roof. This will allow HKU and CLP to gauge the sustainability of the project and to improve designs, if needed, for any future developments.

For the future, Professor Jim hopes the CLP substation in Tseung Kwan O will be a living demonstration of the benefits of green roofs and green walls, and how they can be used in built up areas.