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Case Studies

Bruntwood Green Roof

Category: research

STRI was commissioned by Polypipe to design and install a ground-breaking blue-green roof system on Lowry House, Manchester. As this was a complete design and build project and required specific expertise at all stages of the project, STRI benefitted from strong synergy between all 3 companies within STRI Group – STRI Ltd, EPG and Carrick Sports Construction. The project, instigated by Bruntwood Works, was the first of its’ kind in the area and is part of a larger project transforming a traditional office block into an environmentally friendly and vibrant new workspace.

City tower looking over the green roof

The design of the blue-green roof was jointly undertaken by STRI and EPG (part of the STRI Group). EPG designed the blue roof element in line with all local and national guidance and frameworks, utilising Polypipe’s Permavoid system in order to provide attenuation, which was then used by the green roof as passive sub-surface irrigation, 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; utilising 3 of the existing outlets and therefore enabling the removal of the additional existing outlets, which then resulted in more space within the building.

 

As well as reducing the flood risk with intuitive water management technology, there was also a metaphorical eye on biodiversity amid the hustle and bustle of Manchester city centre, and therefore STRI specified a special lightweight green roof substrate and bespoke wildflower mixtures designed to attract pollinators and survive the tough conditions on the roof.

The green roof provides a habitat for wildlife in Manchester city centre

A further benefit to this project is that the blue-green roof will be used and studied by United Utilities in order to assess how the methods used on this project can reduce the volume of surface run-off entering the sewer network by storing and re-using rainwater which could then lead to additional technological developments in water management and reducing flood risk.

 

In order to ensure the roof meets current blue roof storage requirements, EPG conducted extensive design and storm calculations. This then provided further benefits in 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 installed waterproofing and installing an impermeable polyurethane spray applied foam to create a flat base for the installation of the Permavoid blue roof system.

 

Weight was a constant issue in the design, with EPG and STRI both limited in both the amount of water that could be stored on the roof, and the density and depth of green roof substrate. Combined this made the design very challenging, with special consideration given throughout the design to ensuring the vegetation would survive long term on the roof whilst keeping weight to an absolute minimum.

The blue below the green

STRI’s construction arm, Carrick Sports Construction 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 in order to adapt to the circumstances; this meant that rather than a standard delivery of materials and machinery, this was staggered over a number of days and were all early morning deliveries. In addition to this, the movement of the materials and machinery from kerbside to rooftop was undertaken as quickly as possible in order to minimise any 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 in order to prevent irreversible damage. The initial construction schedule of 3 weeks was beaten by 1 week by a combination of long days and careful planning by the Carrick team.

A sunny day in Manchester

The Results

Industry changing smart blue-green roof technology

Provided a habitat for wildlife in an incredibly busy and built up city centre

Completed the project ahead of schedule

Minimum disruption to the surrounding area due to meticulous planning and forward thinking

Reduced flood risk in the area

Provided a research opportunity for United Utilities and Manchester City Council

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