Construction of a Retrofit Brown Roof in Toxteth, Liverpool, UK

Project Background

Toxteth TV is an education facility for children and young adults who have an interest in pursuing a career in media. As part of an ongoing improvement programme it was decided to install a brown roof (also known as a biodiverse roof) on one of the facility’s buildings, John Archer Hall – a former school building dating back to the Victorian era. It is intended that the brown roof will help reduce energy bills, provide an education feature, and help increase city-centre biodiversity.

Planning consent for the project was obtained from

Liverpool City Council, as “engineering operations” and “change of use” permission was required.

Brown Roof Construction

The brown roof was constructed by specialist contractors, Evergreen Roof Gardens, using a simple layer build-up designed to minimise lifecycle cost.

A waterproofing membrane incorporating a root barrier was first laid on the roof. This was followed by a drainage layer consisting of an Oldroyd separation fleece, an Oldroyd Xv 20 GreenXtra drainage layer (min 49% recycled). Finally 50 – 150 mm of substrate was laid on top of the drainage layer. The depth of the substrate was deliberately varied between 50 and 150 mm to encourage diverse flora establishment.

Biodiversity Features and Disabled Access

Access to the roof is provided by lift and a wheelchair-compliant path was installed along the length of the roof.

To try and maximise biodiversity on the brown roof, a wide range of substrates were used. These included crushed brick, English rounded pebbles, iron sand, and formulated soil. To encourage quick colonisation of the brown roof it was seeded with a wildflower mix obtained from the National Wildflower Centre in Merseyside.

Landscaping features including rainwater pools, pebble mounds, and small “log piles” were included in the roof design to encourage biodiversity. It is also intended that bat boxes and bird boxes will be installed in a sheltered area near the main roof.