In a greening system in which the rooftop and 4F/3F terraces are connected by water-retentive downspouts, the runoff delay effect and rainwater storage effect on each floor were observed. The effect of delaying the outflow peak was less than 1 hour throughout the period. The storage effect was high on the rooftop and 4F, reducing the storage load on the lower floors. In the model section, the total runoff reduction ratio was 8.77% to 95.50%. In particular, storage on the 4F terrace was considered to be important for reducing the outflow load of the entire greening system.
