In cooperation with

Walthamstow Stadium

Our geocellular stormwater attenuation system was specified due to it’s ability to work perfectly as a sub-base replacement system, avoiding deep excavation at the site which contained contaminated ground and a high water table.

London, United Kingdom
London & Quadrant Housing
Water capacity
1,5 million liters of stormwater storage


A closer look at this build-up at Walthamstow Stadium:

The Permavoid system is capable of handling rainfall in the event of a‘1 in 100’ year storm, and reduces urban stormwater run-off from the site by 80%.

Utilising the high strength Permavoid system,we designed and supplied the system beneath 4,500m2 of permeable paving to provide 1,500m2 of stormwater attenuation.


High strength needed

The design featured 150mm deep Permavoid cells, with Permafilter geotextile laid on top between the cells and the permeable paving. The Permafilter acts as a barrier to capture and treat surface water run-off at source from the permeable paving above, before entering the tank. The sides and the bottom of the tank were wrapped in a geomembrane to allow for stormwater to be attenuated, before discharging at a rate set by the Environment Agency into the river with the use of flow control devices. In areas of hard standing, without permeable paving, Permachannel and Permavoid Biomat were installed to capture, treat and attenuate surface water run-off.

Despite being so lightweight, the strength of the Permavoid cells allows them to support structural loads across heavily trafficked areas, making them suitable to withstand the compressive and dynamic loads produced by vehicles at the site.


How does it work

The goal is to slow the flow of water into the sewer during periods of rainfall by detaining stormwater on-site. Creating substantial stormwater detention volume in a densely build area is not easy, but with backing of Thames Water, the Borough and Transport for London a design was created with the detention volume in Permavoid units directly below the road surface. Rainwater enters the Permavoid detention system through a permeable asphalt road surface layer and prior to entering the storage tank, water passes through the PermaFilter geomembrane to remove any oils and other vehicle pollitants.

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Permavoid source control ensures that no precious water goes to waste by catching, storing and reusing stormwater for irrigation, evaporation and infiltration. Find your local Permavoid distributor here to learn more about the technology and become part of the international movement.