Green Roofs in Urban Underground Buildings: Design Impact on Perceptual Comfort

The green roof is mostly affected to the urban people where they can have natural ambiance within their daily activities. It can also be applied to underground roofs, but still needed to get attention to affecting the comfort of working underground. This study will analyze the effect of the green roof on the design of the Underground Gas Insulated Substation (UGIS) as a case study of underground buildings. Using one of 3D modelling program, Sketchup, to create underground building model include green space area, the underground building can be visually presented to the next respondents. This model will be used as a refference to gain people’s perceptions of the existence of green roof on their underground buildings. The results of this study indicate that the allocation for the use of the UGIS green roof area is 26%. Moreover, based on the questionnaire and after presenting the 3D green roof model, most of the respondents felt that their workspace on the surface so far had fulfilled their perception of comfort both thermally, visually and audially. Respondents’ perceptions indicate that visual comfort is of more concern to determine the comfort level of work if they are moved from the surface workspace to the underground workspace. This study showed that beside the green roof can affect public benefits such as reducing the urban heat island effect, managing rainwater, and reducing air pollution, it can also enhance the perceptual comfort. One of the most significant constraints of green roofs in underground buildings is the higher initial cost compared to conventional flat roofs. Therefore, this intensive provision will reduce green roof initiation costs so that green roof investment feasibility can be achieved and make it easier for building owners to calculate the return on their green roof investment.