Developed cities such as Hong Kong are usually densely populated. Since the land is limited, high-rise buildings are constructed. When the building height becomes higher, air flow is reduced and heat is trapped among high-rise buildings. Air temperature will be greatly increased and air pollution becomes a serious problem. This creates a walled building problem. To reduce air temperature caused by the wall-effects, various methods have been developed in the previous studies. One typical method is the use of green roof systems. The application of extensive green roofs on the existing building rooftops has been recommended in Hong Kong since 2001. The advantage of this practice is that no additional floor area is required and it can also improve urban greenery. Although a green roof system has been introduced and adopted in Hong Kong since 2001, the emphasis is mainly given to the application of intensive green roofs for podium garden instead of extensive green roofs. It is considered valuable and necessary of the extensive green roofs for the buildings. This paper investigates the current practice of using extensive green roofs in Hong Kong. The constraints in applying extensive green roofs are investigated, which leads to studying the solutions for mitigating these constraints and improving the future development of the implementation.
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