From the ‘urban heat island’ to the ‘green island’? A preliminary investigation into the potential of retrofitting green roofs in Mongkok district of Hong Kong

Like many densely populated metropolises in the world, Hong Kong is suffering from urban heat island (UHI) effects due to rapid urbanisation. This study provides a preliminary investigation into the green roof retrofit potential in the densely occupied old urban district of Mongkok in Hong Kong. Results of focus groups discussions indicate that adequate exposure to sunlight and the longevity of the rooftop structures of the existing buildings are considered as critical enabling factors for the green roof retrofit. Key barriers to green roof retrofit included the availability of adequate roof space, the appreciation by the industry and the general public, insufficient incentive programmes and movements from government. The 3D simulation models developed in this study suggest that there are 17 rooftops (i.e. 5.8% of total area) in the region affected by overshadowing in winter and over 50% of the area of these rooftops fail to receive direct sunlight during the winter-spring time. The results further revealed that 16.3% of total roof areas in this region are covered by rooftop HVAC plant and equipment. This study offers a simple and low cost preliminary approach for designers and property managers to determine the potential of their stock for green roof retrofit.

► Challenges and barriers to the potential green roof retrofit in HK are discussed.
► Simulation models are developed to study the feasibility of green roof retrofits.
► Fifty percent of rooftops fail to receive direct sunlight during the early spring.
► Model showed that 5.8% of rooftop affected by overshadowing in winter.