Anyone who lives on the Rhine or Elbe has already dealt with the issue of flooding. But far away from the major rivers, cellars can also leak: due to heavy rain. In principle, it can pour out anywhere in Germany and cause considerable damage. Small rivers can suddenly swell into raging torrents; But sealed floors, a location on a slope or in a hollow can also concentrate the rain into a tidal wave that overwhelms the local sewer system – or pushes it directly into the house. With climate change, such weather events are likely to become even more severe over the years.
If you enter the name of your community and “heavy rain map” into your internet browser, you will usually find an interactive map showing which path the water is taking. This allows you to assess how at risk your own house is. North Rhine-Westphalia is exemplary: The state has combined all municipal maps on one website, although municipal maps often have a better resolution.
Unlike river floods, it is difficult to predict where heavy rain will cause floods. That’s why it’s important to take long-term prevention. Wherever it makes sense to place sandbags in front of the entrance to the underground car park or the basement windows, these must always be ready. In addition, the weak points of the house should be identified and remedied (see below).
Save something quickly, you shouldn’t give in to this impulse lightly. Just at the beginning of May, a man in Hausen (near Würzburg) died of an electric shock while climbing down into his basement. As soon as the water reaches sockets or electrical devices, there is an immediate danger to life. It may therefore be worthwhile to switch off the electricity in the basement as a precaution before the storm.
The water pressure is also tricky: Once the water is in the basement, doors can sometimes no longer be opened against the pressure of the water.
It is better not to store valuable items in the basement. The sockets should be located at the top – and no multiple sockets should dangle down. Used oil or half-open paint pots can also take a bitter toll if water gets into the basement. A basement that can get damp should be painted or tiled to make it waterproof rather than wallpapered.
When it pours out of buckets, the sewers fill up. Rainwater and wastewater usually flow together into a sewer system. If this is overloaded, the wastewater can no longer flow away, pushes back into the basement – and can even come out of the drains higher up in the house. The house must therefore be properly secured with a backflow flap or a lifting system. As a rule, this is also mandatory.
Nevertheless, insurance experts report that in the majority of the houses they inspect, this protection against backflow is not sufficient. The backflow of wastewater after heavy rain is by far the most common cause of damage. And the best insurance is of no use if it is not regularly maintained. A common cause of the flap not closing properly is rubbish that has been carelessly thrown into the toilet. Panty liners, diapers or leftover food can get stuck on the flap.
The damage in the basement is regulated by household contents and residential building insurers. The former on the furnishings and things, the latter on the building. However, only if so-called natural damage was also insured. Some insurers even rule out damage caused by backlogs, consumer advice centers warn. So it’s better to check the fine print!
If the house is flooded, residents should do what they can to reduce the damage – as long as it is safe to do so (see above). This is what the insurers require. Before doing so, you should definitely document the damage with photos and videos, otherwise it may be difficult to get a refund. It is also advisable to document the maintenance of the backflow protection.
The light wells in cellars are often a sore point: they usually have no water drainage; a small pool is created in the well from which the water presses against the pane. Either the panes must be pressure-resistant or the light shaft is protected with flaps or walled in.
Gutters are often not cleaned and leaves and moss accumulate. Many people think that this is not a problem, but the water often finds its way into the roof, onto balconies or other places where it can press into the house. Sometimes in old houses there are old drains that direct water from outside into the house drain. If the backflow then works as well as desired, this water cannot drain away and runs into the house via the drains.
In Idstein, Hesse, the underground car park of a police station recently filled up so quickly that the garage door could no longer be opened. In inner cities, new buildings are increasingly being fitted with underground car parks. The access ramp is often a gateway for heavy rain, as the small collecting channel at the entrance is not designed to handle large amounts of water. It becomes dangerous when an electric car is also charging at the wall box – and the water running in could potentially become electrified.
It is also important not to endanger yourself in the underground car park. The Flood Competence Center recommends that you no longer drive your car out when the water level is ten centimeters high.
If you want to protect your home against heavy rain, you should first check how big the risk is using the municipal maps (see above). Then there are useful checklists that can be used to systematically work through all points of attack. The e-book “Severe Weather Building Check” (as a PDF) from the consumer advice centers and the information from the Flood Competence Center are particularly suitable.
Sources: Consumer advice center, Flood Competence Center (HKC), Federal Ministry for the Environment and Consumer Protection (BMUV), tagesschau.de, Hessenschau, R V