Water Retention with a “Stormwater Management Roof”

Why a “Stormwater Management Roof?”

Changing weather conditions (e.g. extreme local rain events) can result in an entire public sewerage system being overwhelmed. One of the great benefits of a green roof is that it detains water and allows for the time-delayed run-off of stormwater (water retention).

Water storage in a standard green roof build-up cannot be increased arbitrarily because more water could result in changes to the vegetation used. However, this is possible with a “Stormwater Management Roof” which offers this option in addition to all the other features of a green roof build-up.

Features of a “Stormwater Management Roof”

With a Stormwater Management Roof a large portion of precipitation is detained on the roof area and is then released into the drainage system during a predefined period. The space required for the increased precipitation is created by a grid spacer situated beneath the actual green roof build-up. Meanwhile, the elements that are of vital importance for the proper functioning of the green roof (water storage for the plants, air-water household in the root area etc.) are all preserved. 

Virtually all types of roof utilisation are possible above the stormwater retention space, once structurally permitted, from an extensive green roof to a roof garden with pathways and driveways.

System build-up “Stormwater Management Roof” Type “Roof Garden”

Notes: 

* The values apply if the full accumulation capacity of the retention spacer RS 60 (left side of the figure) is used. The weight of the vegetation must be taken into account additionally (see FLL Green Roof Guidelines, table 26).