The purpose of Southern Water’s £300 million environmental improvement scheme is to treat 95 million litres of wastewater a day. Part of the scheme, the Peacehaven Wastewater Treatment Works was to feature a grassy roof expanse, concealing the various buildings underneath and enabling them to blend into the rolling hills surrounding the site.


The Challenge

Creating the curvaceous profile and cantilevered construction of the 17.800m2 green roof was fundamental to the project success.  As well as being sympathetic to the landscape, the grass-covering would enhance the site's biodiversity by providing a habitat for downland plant species and creating a secure environment for nesting birds. It also needed to attenuate rainwater run-off and offer excellent thermal insulation.


The ROCKWOOL solution

The sustainable roof construction is a warm flat roof system that utilises the ROCKWOOL 85mm HARDROCK® Dual Density range of tissue faced insulated roofing boards. These feature a robust, high density top layer with excellent point load compressive resistance and provide a non-combustible, acoustic and thermal insulation solution, which is compatible with Alumasc's Derbigum Anti-Root, high performance roof waterproofing membrane. A green roof system was installed on top of the waterproofing.

The roof was constructed using a profiled metal deck, supported on purlins and covered with a vapour control layer.

In addition to roof insulation, ROCKWOOL insulation products have also been used in the construction of the scheme's walls. These are constructed from green-coloured, ribbed metal cladding, designed to blend with the surrounding landscape. A flexible mat of ROCKWOOL Cladding Roll was used in the wall to satisfy the designer's thermal, fire and acoustic requirements.


The Benefits

  • ROCKWOOL products save more than 100 times the energy invested in manufacture, transport and ultimate disposal. 
  • Thermal, fire and acoustic benefits.
  • At the end of the building life, insulation can be removed and recycled.
Project Location

Peacehaven Wastewater Treatment Works

BN10 8GN

Given the complex shape of the roof, ROCKWOOL was the most suitable product because it offered a degree of flexibility

Paul Webb

Project Manager
The advantage of using ROCKWOOL is that in addition to its recognised properties, its use in conjunction with Derbigum provides an extremely durable and long-term waterproofing solution.

Trevor Lang