Sustainable drainage systemsSuDS

A flat roof designed to attenuate rainfall by temporarily storing water on the roof and releasing it at a controlled rate through restricted outlets, reducing peak loads on drains and watercourses. Blue roofs form part of sustainable drainage (SuDS) strategies and place high demands on the reliability of the waterproofing and the structure.

A roof deliberately covered with growing medium and vegetation over a waterproofing system, usually incorporating root barrier, drainage and filter layers. Extensive green roofs use shallow substrates with low-maintenance planting such as sedum, while intensive green roofs support deeper, landscaped schemes. They contribute to rainwater attenuation, biodiversity and reduced urban heat island effect.

The effect whereby built-up areas are noticeably warmer than the surrounding countryside, because dark, dense surfaces absorb and re-radiate solar energy while there is less vegetation and evaporative cooling. Roofing measures such as reflective cool roof surfaces and green roofs are used to mitigate it.