2.2. Green roof installation and experimental designAt Block 1, roof BTI layers were omitted to emulate a poorly-insulated building (Fig. 1). At Block 2, normal BTI layers wereinstalled. Both blocks contain normal waterproof membrane res-ting on a screed layer placed on reinforced concrete slab. Thethermal insulation and waterproof design and materials are com-monly adopted in Hong Kong. All apartments have main windowsfacing southeast. To standardize their environmental conditions,small side windows of the terminal unit at each block were shieldedby thermal-insulation gypsum boards. Windows and doors werekept closed in the study period to minimize external influence ontemperature.Identical experimental designs were adopted at both blocks.Each block’s roof site of about 85 m2is divided into three roughlyequal plots, which correspond to the three apartments lying under-neath (Fig. 2). Plot A (control plot) was left bare to serve asthe baseline. Plots B and C were assigned to two green rooftypes. A proprietary green-roof system (Nophadrain, Kirkrade, TheNetherlands) conforming to stringent German specifications (FLL,2008) was installed. The sequence of its multiple materials layersis shown in Fig. 2.