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4.3 The rainwater drainage system
The roof construction design draws the rainwater to specific collecting points at
the level of the four-legged supports. Each one of these collecting points is to
ensure water drainage for 700 m² of roof surface area. In the case of heavy rainfall
this represents a flow capacity of roughly 35 l/sec.
The water to be evacuated is concentrated in a space which forms a funnel above
the support bases. Potential weight-bearing is prohibited. The system consists of
two lowered roof drains (Pluvia) and allows a higher evacuation flow rate while
utilizing smaller diameter pipes. This reduced diameter of 90 mm is necessary to
allow pipes to pass through the steel pipes of the four-legged support. As a safety
measure, two more backup drains are placed a few centimetres higher than the
main ones. In this way, rainwater evacuation is maintained even in the case of
malfunction or excessive rainfall. The 4 water evacuation pipes in PEHD run down
through the four bases of the supports to the platform level inspection holes. The
inspection holes of one platform drain into a 600 mm wide main collector which
runs into the sewer.