Polypipe selected the Permavoid system for a prestigious London residential development. The Permavoid geocellular stormwater attenuation system was specified due to its 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.
Located on the site of the former greyhound stadium and adjacent to the River Ching, the Walthamstow Stadium development boasts 294 new homes that incorporate sustainable drainage features, including brown roofs and permeable paving.
Utilising the high strength Permavoid system, Polypipe designed and supplied the system beneath 4.500m2 of permeable paving to provide 1.500m2 of storm water attenuation to meet the requirements of the Environment Agency.
The design featured the Permavoid 150, with Permafilter geotextile laid on top between the units 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 storm water 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.