A parapet is a low protective wall along the edge of a roof, bridge, or balcony. In this case we are discussing about the its influence on the wind pressure when the roof is flat. The wind pressure is passing trough every single inch of the flat roof so it has a different influence on every corner and side.   These schemes presented in the gallery are showing exactly the influence of the parapet on the wind pressure when the roof is flat. Here is how:

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