ABG blueroof - Biodiverse & Amenity Podium Areas, The Post Building, London, UK

The Post Building development completely remodels the former Royal Mail Sorting Office located on New Oxford Street in Central London into modern Grade A offices, with street level retail and restaurant space along with rooftop gardens, terraces, and leisure areas. The project received a prestigious RIBA London Award in 2022 and the main roof terrace is open to the public, providing panoramic views over the city.

In order to gain planning approval, the development had to be repurposed in line with the ‘SuDS manual’ best practice guidance to minimise surface water run-off in the event of a storm and in order to meet the maximum discharge consent limits set by Thames Water.

Basement SuDS storage is expensive and often impractical to achieve in city centre locations. ABG’s blueroof system was therefore chosen as an easy to install alternative to provide stormwater attenuation at roof level. The system is installed across three main roof areas and includes 14 restrictor chambers positioned above rainwater outlets to limit the outflow rate. The system is calculated to control stormwater in the event of a 1 in 100 year storm, based on the local Flood Studies Report (FSR) rainfall data, plus 30% allowance for climatic change.

The roof design incorporates a variety of surface finishes, including a resin bound play area, biodiverse green roof areas and paved & decked terraced areas. The roof also includes solar PV arrays and planters supported on top of the blue roof.

The ABG blueroof system drains like a normal roof during everyday rainfall events, but throughout the critical design storm periods restricts stormwater run-off, continuously releasing rainwater at a controlled rate until empty.

The discharge rate is site specific and forms part of the scheme wide SuDS plan, and means that other downstream measures are not required. The scheme also included sedum green roofs to improve site biodiversity across two further areas.

ABG provided project design calculations and all blue roof materials required for the different roof levels, plus our installation service.