Green Roof Direct Cost and Benefit Comparison for Flash Flood Mitigation via Urban Storm Water Runoff Reduction

An impervious surface generates high storm water runoff volumes which overwhelm drainage systems caused frequent urban flash flood episodes. Green roof is a highly efficient green infrastructure in reducing urban storm water runoff. Studies have agreed on most important green roof characteristics that contributed in reducing storm water runoff are substrates depth, type of vegetation, and roof slope. However, to date, no study has drawn a connection between these performances and cost that contributes to the performance. This is important as cost is the utmost barrier for green roof implementation. Therefore, this study motivates to assess cost and benefit of substrates depth, type of vegetation, and roof slope for intensive and extensive green roof. Roof slope is the utmost cost-efficient green roof characteristics for storm water runoff reduction at 1: 1.5 and 1: 2.2 for extensive and intensive green roof. Type of vegetation contributes to the highest cost for both green roofs. Substrate depth is only cost-efficient for intensive green roof at ratio 1: 1.4. This study is significant in encouraging building owner and investor to implement green roof by providing substantial evidence on it efficiencies and cost that contributes to the effectiveness. This will eventually promote the growth of green building within building sectors.