Prater realizes the largest curved green roof in Great Britain

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Prater, the specialist for roof systems within the Lindner Group, has recently completed works on the largest domed green roof ever to be installed in Great Britain. It now adorns the 300-million-pound wastewater treatment plant serving the catchment area around Brighton and Hove in the south of England.

Prater, the specialist for roof systems within the Lindner Group, has recently completed works on the largest domed green roof ever to be installed in Great Britain. It now adorns the 300-million-pound wastewater treatment plant serving the catchment area around Brighton and Hove in the south of England.
Thanks to a matured concept Southern Water, a local water company, was after initial delays finally able to gain planning permission for the plant in Peacehaven, East Sussex. The facility covers an area of 17,800 m², the equivalent of 2 1/2 football pitches.

General contractor 4Delivery (4D) contracted building envelope specialist Prater and the architect firm  Montgomery Watson Harza (MWH) with the development of a revised design that included the landscaped rooftop installation. In October 2008 the minister responsible officially approved the design. Construction works commenced as early as July 2009 and are to be completed in April 2012.
“Since a lot of money has been invested over the past ten years into this project, we were searching for a cost-effective and yet still environmentally-friendly solution”, explains Phil Risbridger, the head of the joint venture consisting of Costain, Veolia Water and Montgomery Watson Harza.

“Normally these two requirements are hard to marry up successfully, but Prater suggested a new system to us whereby a single-layered roof terrace made from metal is covered in turf. The time and costs that we have saved through this helped us in making up for the delays.  At the same time it also helped us to meet all environmental targets that Southern Water had set itself. “

The biggest challenge on site was logistics. Several thousand tonnes of substructure had to be transferred onto the roof which was then covered completely using mobile tower cranes. The problem was overcome with several conveyor belts that distributed the material evenly across the area so that it moulded itself perfectly following the structure’s contours.

Paul Webb, Project Manager at Prater, describes Peacehaven as “a milestone in the company’s project history”.  “A green roof of these dimensions and of such a composition has never before been attempted, which meant we had to prove that we could develop a system that can indeed carry the substrate material.”

“The metal deck single ply structure with shear batten support overcame initial design concerns. Specifying a fully turfed landscape – rather than the standard sedum green roof – project leaders wanted to cover the entire area with turf. In the last instance this convinced the planners that this would be perfectly befitting the surrounding countryside. “

Horticultural expertise was fundamental to making the installation possible in the first place and also for the long term viability of the green roof.  The seed mix was carefully chosen so as to blend in with the natural surroundings and so as to react with the seasons in the same manner as the immediate landscape around the facility. Extensive planning furthermore ensured that the turf was established and hardy enough from the outset. The turf was grown offsite for 15 months in a controlled environment away from the construction site. In order to minimize any potential negative effects during the replanting process great attention was paid to ensure that the time span between excavation and replanting on site did not exceed 24 hours. In future the area will be trimmed at regular intervals in order to keep the building load to an optimum and maintain the healthy condition of the lawn. Prater supplied the complete solution for the building envelope of this project, which when finished will be treating 95 million litres of wastewater every day.  The entire building project included the erection of a new wastewater treatment plant, a sewage sludge utilization plant and an 11-km long underground pipeline that feeds the wastewater to Peacehaven.