Can blue sky thinking lead to
blue roof inspiration? Carl Harrop
Increased flooding instances in the UK continue to drive regulators to reduce the impact that the built environment has on drainage infrastructure and watercourses. Using the planning system as a vehicle for regulation, it is now commonplace for developers to be required to include SuDS (Sustainable Drainage Systems) into developments.
S
ustainable Drainage Systems aim to control surface rainfall run-off by controlling the rate and volume of runoff from a site, relieving pressure on sewerage systems and mimicking natural drainage as closely as possible. Many of the common SuDS components, such as infiltration (drainage into the ground through swales for example) are implemented downstream of individual buildings, making it impossible to include in dense urban environments. The tendency was therefore for the requirement to centre around the attenuation of rainwater flows from individual buildings. This attenuation (slowing) of rainwater flows was typically achieved by introducing large tanks, often in the Basement or Ground floor of the building, to intercept the rainwater. The water is then released at a considerably decreased flow rate into the downstream infrastructure. There are several drawbacks to this approach, including; • The use of valuable floor space for the storage • It sometimes requires pump discharges (very unsustainable)
• The tank will be sized for the worst-case storm (typically 1:100 years plus a climate change allowance of 40%) and hence it will sit largely unused for probably large portions of the building life.
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Blue roof overflow
Source control SuDS is where the rainwater is managed where it lands, which for most city centre buildings will be the roof or podium. A technique which embraces this perfectly is commonly referred to as a blue roof. A blue roof is specifically designed to provide source control, managing it where it lands, by temporarily attenuating it on the roof by limiting the flow thorough the rainwater outlets, causing water to build up across the roof. This provides an excellent attenuation of flows without any additional land or floorplate take. The reduction in the number and size of the rainwater
