Bruntwood Blue-Green Roof

The fundamental purpose of the Bruntwood blue-green roof is sustainable water management. This has been achieved with our water management team, STRI’s design and environment teams alongside Polypipe and Kisters, with the installation being undertaken by STRI Group’s construction arm, Carrick Sports. Bruntwood Works aim is to make their stylish office buildings as sustainable as possible, both inside and out. Therefore, the blue-green roof was retrofitted onto an existing roof, and utilised Polypipe’s Polysync and Permavoid systems. This project benefitted from the synergies of our end to end in-house teams.

“We’re developing the most innovative workspace in our cities. The idea is that we’re embedding six key pillars into our design and part of that is sustainability and biodiversity and we thought that because of those two key pillars, the blue-green roof would fit perfectly in to our ambitions” – Adam Tillis, Building Director of Bruntwood Works

The Project


  • Blue roof element needed to be designed in line with all local and national guidance and frameworks
  • Varying levels of rainfall throughout the year needed to be considered, with Manchester being subject to dry spells and periods of excess rainfall. This meant that a system needed to be developed to successfully manage both occurrences
  • Weight capacity of the roof was limited, meaning that calculations had to be undertaken to understand the amount of substrate to use in addition to limits on how much water could be retained and the weight of the wildflower 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.

“It’s really important that more initiatives like this happen. Personally, I’d like to see it become more and more mainstream.” – Sophie Tucker, Area Engineer Manager at United Utilities.



  • By deploying the Permavoid and Polysync systems together, any water that falls onto the roof is captured and stored underneath the substrate layer by the Permavoid attenuation tanks, to be recycled for passive sub-surface irrigation of the vegetation above
  • The Polysync system, alongside the Permavoid, means that the water within the Permavoid tanks remains at an adequate level, not only by retaining water for irrigation but also by ensuring that water levels don’t exceed those recommended
  • United Utilities are studying this technology at Bruntwood to determine whether this system could be replicated across whole cities and reduce flood risk on a much larger scale, preventing stormwater runoff from entering the sewage system and polluting water sources
  • More space within the building
  • Provided a habitat for wildlife in an incredibly busy city centre
  • Project completed ahead of schedule