Project Description
Formerly owned by Royal Mail, 160 Old Street is a nine storey office redevelopment scheme in London, designed & developed by Great Portland Estates and Orms Architects on behalf of the Great Ropemaker Partnership. The 160 Old Street redevelopment won twice at the BCO Awards in the categories of best London ‘Refurbished / Recycled Workplace’ & ‘Innovation’.
The Challenge
The 14,920m² office space comprises a complex array of 29 different roof zones over multiple floor levels, with 16 of the areas designed with blue roof SuDS attenuation, biodiverse roofs and/or composite decking. The SuDS measures were needed to meet the National Planning Policy Framework (NPPF) & local planning requirements to slow surface water run-off during key extreme rainfall events.
The Solution
The ABG blueroof system was deemed the most cost-effective SuDS solution for the urban site, with the construction of a basement attenuation tank deemed impractical and expensive.
By retaining the attenuation within the building footprint, blue roofs are ideal for urban environments where ground space is limited. During moderate rainfall events the water permeates through the blue roof system and into the roof’s rainwater outlets as normal.
ABG’s blue roof system – an ‘at source’ SuDS solution
In the event of high intensity and prolonged rainfall events, the ‘blue roof’ attenuation voids start to backfill as rainwater is slowed to an agreed maximum discharge rate by the restrictor chambers. The water is allowed to continuously drain to half-empty over a maximum period of 24 hours; but helps to control the overall site discharge rate and prevent surges into the local sewer networks.
ABG’s blue roof SuDS attenuation system is very versatile, allowing a combination of surfaces; including composite decking on amenity areas and biodiverse and ballasted areas across the different levels. The maximum discharge rates were calculated by ABG in accordance with the engineer’s SuDS drainage strategy and the overall planning requirements. ABG’s UK manufactured combined reservoir / drainage geocomposite boards were also used for the biodiverse and green roof areas. These reservoir boards help to retain the optimal amount of water during dry periods and allow planting a better chance to flourish.
160 Old Street – a complex array of 29 separate roof areas and surface finishes
The ABG Service
In total, 976m² of blue roof attenuation was designed and installed to restrict maximum discharge rates to 23.1l/s during the key ‘1-in-100 year +30% allowance for climatic change’ storm event. For the biodiverse roof areas, an undulating growing media, a London wildflower seeding and various hibernacula were installed (i.e. stone, sand piles and native hardwood log piles) to support invertebrates and other wildlife. A regular maintenance service was also included as part of the contract, as now required for all SuDS processes, to gain planning approval.
