Bruntwood Blue-Green Roof

STRI designed the blue roof element in line with all local and national guidance and frameworks, utilising Polypipe’s Permavoid system to provide attenuation for the 100-year storm event. Additionally, an extra 40% was added to peak flows across the roof deck to account for and counteract the effects of climate change, whilst also allowing the removal of one of the four existing outlets, resulting in more space within the building itself.

Polysync is a smart controller of water that acts as a forecasting hub using Kisters’ cloud-based intelligence system, meaning that it transmits data from the forecast to open a valve to release the correct amount of water in advance of rainfall and storm events. This reduces flood risk to the surrounding areas.

Weight was a constant issue in the design, with limits in both the amount of water that could be stored on the roof, and the density and depth of green roof substrate. These considerations made the design challenging, with special consideration given throughout the design to ensuring the vegetation would survive long term, whilst keeping weight to an absolute minimum and also adhering to current blue roof storage requirements. This was achieved by aiding the reduction of water volume discharged by the roof into the United Utilities network whilst also ensuring that the structural strength of the roof deck wasn’t overwhelmed. This included undertaking a survey of the existing waterproofing and installing an impermeable polyurethane spray-applied foam to create a flat base for the installation of the Permavoid blue roof system.

The wildflower roof offers a more diverse ecosystem from the plants themselves and the flying insects they attract, such as bees and butterflies, in addition to the aesthetic benefit and the energy-saving properties of the roof. This relates directly to the insulation properties from root vegetation, resulting in the building staying cooler in the summer and warmer in the winter, reducing energy consumption and further counteracting climate change.

STRI Group’s construction arm, Carrick Sports, installed the roof in June 2021 over the space of two weeks. Due to the inner-city location of the site and consequent lack of storage facilities, there was a need to deviate from normal procedure; this meant that rather than a standard delivery of materials and machinery, this was staggered over a number of days, using early morning deliveries. Also, the movement of the materials and machinery from kerbside to rooftop was undertaken as quickly as possible to cause minimal disruption to the local neighbourhood. However, this then posed additional challenges as we needed to ensure that the maximum weight capacity of the roof was not exceeded at set points. Due to the high temperatures experienced during the build, the bespoke wildflower turf also had to be laid rapidly and heavily irrigated to prevent irreversible damage. The initial construction schedule of three weeks was achieved in just two weeks through a combination of long days and careful planning.

Following exhaustive research, the roof was installed in June 2021 and will be managed and maintained by STRI until June 2024.