The word “retention” in water management refers to a balancing effect in water storage instead of draining runoff water into the pipe system. The need for retention grows as the weather conditions change (e.g. local heavy rain), otherwise the rainwater drainage system may become overloaded.
First, most rainwater is retained in the roof area (when a runoff water management solution is in use) to full flooding management extent and released into the water discharge system after a predetermined time period has passed (e.g. 24 hours). All elements important for the functionality of the green roof have been included (water storage for plants, air/water for the root area, etc.).
Build-up height: ca. 150 mm
Weight, saturated: ca. 155 kg/m²
Water retention capacity: ca. 80 l/m²