Rainwater

Rainwater from areas below the backwater level may only be connected to the public sewerage system if it is separated from domestic wastewater. The drainage-effective areas below the backwater level that have a gradient towards the building, such as garage entrances, building entrances or excavated areas leading to basement flats, should be kept as small as possible. 

Rainwater from small areas (approx. 5 m²) such as basement access points and similar may be allowed to infiltrate. If this is not possible, such areas may, where a natural gradient exists, be drained via backwater lifting stations with the appropriate approval, provided that suitable measures, e.g. thresholds at cellar entrances, prevent low-lying rooms from being flooded by rainwater whilst the backwater valve is closed. A flood risk assessment is required for this purpose. 

Hybrid lifting stations that drain areas below the backwater level which, if flooded, could endanger buildings or other property must be designed in such a way that no damage can occur in the event of a 100-year rainfall event r(5,100). These areas include, for example, building entrances, cellar entrances, underground car parks, garage entrances and courtyards. For small areas below the backwater level that have a gradient towards building entrances, such as garage ramps, the hybrid lifting station may also be installed inside the building. 

For large areas below the backwater level that do not endanger buildings or property, a flood verification in accordance with DIN EN 752 must be carried out using the 5-minute rainfall event occurring once every 30 years (r(5,30)). In such cases, the hybrid lifting station must be designed to cope with at least the five-minute rainfall that may occur once every two years (r(5,2)).