by Brianna Crandall — July 29, 2016 — With the increase in rain events and flooding and a lowering of the water table as a result of climate change, green roofs can provide additional green space in densely developed urban areas. Each green roof stores a certain quantity of stormwater, and then allows it to run off in a time delay or to evaporate on the roof. The new Stormwater Management Roof from green roof technology company ZinCo uses a spacer to expand this retention effect, and in so doing effectively balance out precipitation peaks.
ZinCo notes that the effect of the current sustained level of soil sealing from a high level of infrastructure development is that stormwater can no longer seep into the ground, and public sewer systems become quickly overwhelmed during severe rain events, resulting in flooding. It is becoming ever more important to implement measures to unseal the soil; for example, city planning authorities are stipulating green roofing in their development plans and are acknowledging by means of reduced wastewater charges the capacity of green roofs for retaining water. This capacity is referred to as stormwater retention, and has considerable potential.
Effects of stormwater retention
The aim of stormwater retention is to suppress precipitation peaks and extend them temporally. For example, a standard extensive green roof stores between 20 and 40 l/m² of water in its green roof build-up, and an intensive green roof stores between 50 and 100 l/m², in some cases even more. With regard to the risk of flooding, a green roof should store as much water as possible, says ZinCo, in order to avoid deterioration of the roof, water logging and root rot. For this reason, ZinCo has developed the new Stormwater Management Roof in two separate parts, the retention volume and the actual green roof build-up.
How it works
In the new Stormwater Management Roof, an element referred to as a “spacer” is used beneath the green roof build-up. The height of the spacer can be varied as required. For example, a 10 cm high spacer allows for the storage of about 80 l/m² of rain, based on a zero-pitch flat roof with the required load-bearing capacity. The retention capacity of the green roof can therefore be increased by a multiple. During a pre-defined period of time (between 24 hours and a number of days), the retained stormwater runs off slowly through a throttle element inserted into the gully and on into the sewer system.
The spacer creates space to store the water, while above it virtually any type of green roof and roof utilisation is possible.
The green roof build-up over the spacer contains all elements that are required for the green roof to function properly — for example, air-water household in the root area, drainage and water storage for the plants. An intensive green roof, naturally, requires a greater level of water than an extensive roof that has drought-resistant sedum plants. Each green roof build-up is therefore adapted to suit the relevant vegetation. Virtually all types of green roof and roof utilization are possible, even pathways and driveways.
This shows the system build-up of the stormwater management with system substrate, filter sheet, drainage element, protection mat, spacer, protective layer and root resistant seal.
Developing the Stormwater Management Roof in two parts allows for a lot of water to be stored regardless of the level of water required by the green roof itself and without any risk of vegetation transformation or water logging.
Building-specific planning
The building-specific values for the Stormwater Management Roof are calculated based on the local climate, precipitation levels, and the required level of retained stormwater. This includes the maximum storage volume, the maximum drainage quantity per time unit, and the period of time required until the water storage area is once again available.
