Especially for the drainage of utilised flat roofs, which also include balconies and roof terraces, the drainage must ensure the required discharge even at a low water level, so that door thresholds, for example, are not flooded. To prevent increased noise generation at the outlet, the drainage system is usually designed for gravity flow.

Aeration openings

To ensure the desired silent gravity flow, outlets for gravity flow feature special aeration openings that allow an air stream to enter the drainage system during drainage. In the case of external parapet drainage systems, the deflection into the downpipe is also designed with aeration openings, which prevent negative pressure from being transmitted from the downpipe to the outlet.