Bay window is one of the most significant features of Hong Kongism. Since the 1980s, the rules of buildable area exemption for bay windows began; Hong Kong entered three decades of the “bay window era”. At the beginning of the bay window is half a meter deep, then the government in order to encourage the use of prefabricated building facades components, exterior wall thickness of 0.3 m is exempted, and the depth of the bay window is therefore increased to 0.8 meters.