Problem Addressed

This solution was sourced in response to UKGBC’s Innovation Challenge: “How can existing buildings be made more resilient to climate change, with as little disruption to their occupants as possible, by 2030?”

The ‘smart’ blue-green roof from Polypipe Civils & Green Urbanisation (applied to Bruntwood Works’ Bloc) is addressing the need to develop greater understanding of how new construction and data technologies can help cities and urban developments to mitigate the impact of climate change and population growth, while enhancing biodiversity.

Solution Overview

This two-year roof research programme will demonstrate the multifunctional potential of green urbanisation. The ‘smart’ blue-green roof will assess how storing and reusing rainwater at roof level can reduce the volume of surface run-off entering its sewer network. It will help lower the flood risk associated with the prolonged high-intensity storm events. Unlike conventional green roofs, which use a drainage layer to remove rainwater, the 525 sq m blue-green structure retrofitted to Bloc’s flat roof stores rain beneath the planted surface where it lands. Advanced passive irrigation components within the attenuation layer draw water up through the structure to the underside of the green roof substrate to support surface planting.

The technology protects green areas during drought, reduces potable water demand during hot weather and enhances biodiversity by maintaining flora in optimum growing conditions. The roof and its outlet are cloud enabled, linking the stored volume to high resolution weather data that maps storm events so the roof is told when a storm is due. Before it arrives, volume is safely released to accommodate arriving rainwater, avoiding any surcharging of the local and downstream drainage network.

The roof reduces the discharge of rainwater and features wildflowers to support biodiversity and provide an additional thermal barrier. This is Manchester city centre’s first wildflower roof which also aims to attract a rare native butterfly, the Manchester Argus.

A review of the existing roof structure is required prior to implementation to ensure structural capacity is adequate for the blue/green roof system. Retrofitting the system had minimal impact on existing occupants as works took place away from building tenants and noise was minimal. No relocation was necessary. Due to the materials needed for the roof, kerbside delivery arrangements with further crane lifting to roof level need to be made.

Indicative investment requirements for a similar project elsewhere:

  • Roof area size – 525 m2.
  • Green / blue roof system size – 462 m2.
  • CAPEX – approx. £150 / m2 for green-roof supply and install waterproofing, insulation, levelling, structural engineering.


  • Financial – possible financial incentives to disconnect surface water from the combined sewer system within the network.
  • Brand and marketing – customers are increasingly expecting businesses to demonstrate how genuine their sustainability strategies and plans are. Bloc is a market-leading workspace, for which the blue-green roof has helped attract new customers aiming to align their business with its sustainability credentials.
  • Biodiversity – Increasing wildflower cover to attract species.
  • Adaptation and resilience – Whilst global commitments towards the Paris Agreement are strengthening, no matter what efforts are made to reduce emissions, the climate will change. Only from the implementation of solutions like the blue-green roof will it be possible to continue to operate and utilise our buildings and wider infrastructure safely and inclusively.

Verification & Case Study

The roof system is currently part of a research project being monitored and reviewed by Salford University. The roof’s effectiveness is verified in a variety of ways:

Managing rainfall as a resource: United Utilities verify the benefits of the roof intercepting and re-using rainfall, to consider how this can impact the drainage system during points of heavy rainfall and to record how much has been used as a resource by the blue-green infrastructure.
Impact on biodiversity: By introducing integrated natural habitats across the urban landscape, this not only creates healthier, more resilient communities that are highly carbon and energy efficient, but also improves the mix of flora and fauna found in the city centre.
Climate resilience: The roof creates additional space to store excess rainfall in the face of increasingly frequent large storm events due to climate change. The water is then stored and reused for passive irrigation delivering a resilient asset that continues to thrive in periods of drought.

The technology installed on the roof is scalable and could be connected to multiple roof spaces and attenuation tanks to offer a catchment-wide solution where water is gradually released into the natural watercourse to make space for large storm events and reduce the risk of flooding. Harvested rainwater can be used for a wide range of non-potable applications across both commercial and residential projects. Reducing potable (mains) water consumption in toilets, laundries and cooling systems, protects drinking water supplies during extended dry spells and can lower overall utility bills.

The project and outcomes will be monitored and reviewed by Salford University across a two year period. Upon completion of the two-year roof programme, the roof will demonstrate:

  • The impact of such a system on surface water runoff.
  • The impact of increased green infrastructure cover in the area.
  • The viability of such a structure in the development process (new build and retrofit).

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