Important: protection against backwater
Site drainage systems must be installed in such a way as to prevent unplanned flooding inside the building or on the site. In particular, the risk of backwater must be taken into account during the design phase. According to DIN EN 12056-4, backwater can occur at any time despite the system being designed in accordance with the applicable recognised rules of technology and being operated with due care.
For economic reasons, public combined and stormwater sewers cannot be dimensioned to cope with every exceptional rainfall event. During heavy rainfall, therefore, blockages in the sewer and backwater in the connecting pipes must be expected. Furthermore, there are many other reasons for backwater to occur:
- unplanned discharges
- overloading due to other obstructions
- blockages or reductions in cross-sectional area, such as root ingrowth
- operational failures in pumping stations
As a general rule, local authorities therefore urge all developers and homeowners to protect themselves by installing a suitable backflow prevention device in order to prevent damage.
Risk associated with the absence of backwater protection
A lack of backwater protection leads to the flooding of buildings, land or facilities. Wastewater from connected sewers and drainage networks thus overflows from the connected drainage outlets. Rooms become flooded and furnishings are damaged or rendered unusable. This poses a risk to human health as well as to buildings and property. In addition to the clean-up costs, there is also a risk of significant consequential damage.
Legal and insurance-related situations
Homeowners must bear the costs themselves in the event of a sewer backflow leading to basement flooding. They cannot hold the local authorities liable for this, even if the local sewers are undersized. Homeowners remain liable to their tenants. Insurance companies may limit or even refuse compensation if the property’s drainage system does not comply with the relevant regulations and technical standards. Consequently, a lack of precautionary measures can quickly become a costly affair.
warranty
Plumbers, designers and property developers are liable under a warranty period of 2 years in accordance with the VOB or 5 years in accordance with the BGB, provided that the system has been fitted and installed in accordance with recognised technical standards. If the drainage system does not comply with recognised technical standards, the warranty period is extended to 30 years. Liability claims cannot be transferred to the customer, even if, for example, the customer wishes to have a product installed that does not comply with recognised technical standards for cost reasons.
