This is an example case of a Detention Roof project in Rotterdam, the Netherlands. Below you can read with which type of rain shower has been calculated and what the results are of the application of the Detention Roof. Within this calculation, all water absorbing components are fully water saturated.
Roof slope
1°
Roof surface
3,412 m2
Maximum permissible roof load
110 kg/m2
Surface Detention Roof
2,953 m2
Maximum roof load Detention Roof
80 kg/m2
Other roof area (vegetation-free zones)
459 m2
Type of roof drains
Pluvia-system ø 100 mm
Number of roof drains
45 pcs
For this water calculation, rainstorm R10 has been used. Due to the current climate change, calculating with R8 showers is no longer sufficient for the current sewer system. During a rain shower R10, 35.7 mm of rain water falls in 45 minutes. The maximum permitted run-off speed on the sewer system is 2.78 litres per second per hectare. When a Detention Roof is applied the calculated peak run-off falls within this standard.
2.69 litres per second per hectare
260.62 litre per second per hectare
In this case the Detention Roof ensures a peak run-off reduction of 99%
1,225 minutes - this means that after 1,225 minutes 50% of the total amount of rainwater has been drained
After 66 hours, the roof stops draining the rainwater
61 mm is temporarily stored and slowed down
35 mm is absorbed in the Detention Roof
Detention is (temporarily) storing water, which is ultimately (delayed) drained. Retention is when the water is absorbed in the green roof layers and eventually is returned to the atmosphere in the form of vapor by the plants (transpiration) and the soil (evaporation). The Urbanscape Green Roll and the Sempergreen Sedum-mix blanket are water-absorbing components. The Detention layer and the Storage layer are water-detaining components.
Would you like to know how a Detention Roof can contribute to your project? Request a water calculation.
Request here