Building and converting in times of climate change and extreme weather

The flood disaster in summer 2021, which claimed at least 188 lives in Germany and caused property damage of 33 billion euros, showed just how serious the impact of extreme weather events can be on populated areas.

"Various current studies assume that these losses will at least double by 2050 as a result of climate change," says Anja Käfer-Rohrbach, Deputy Managing Director of the German Insurance Association (GDV): "There has always been an alternation between years with few and many losses. However, we are noticing that the intervals between them are getting shorter."

In Germany, floods and inundations rank ahead of heavy storms and hail in terms of natural hazards, which generally do not cause fatalities, but cause immense amounts of property damage.

Location of the property as a risk

With these risks in mind, builders and homebuyers should consider the possible consequences of extreme weather when choosing their building plot, advises Florian Becker from the Bauherren-Schutzbund: "This applies, for example, to slopes, which are more expensive to build on anyway, and where, in the worst case, the entire slope can start to move in heavy rain." Properties in a depression where water can collect are also problematic.

A more hidden risk: areas where water once stood, but no longer does: "Street names such as "Aue" or "Graben" can provide clues here," says Becker. There is a risk of problems with the groundwater on all of these properties, as it can rise very quickly and very strongly even with relatively little rainfall.

In general, builders and house buyers in Germany have good opportunities to find out about weather risks to their land. Becker refers to the interactive map of the Federal Institute for Building and Urban Development, which breaks down the natural hazards for individual regions in detail and free of charge: "Some weather hazards are regionally specific, such as strong winds in the north and snow loads in the south. However, a dangerous phenomenon such as heavy rain can occur practically anywhere without much warning."

Check water drainage regularly

Then, under unfavorable circumstances, things become tight for residential buildings: "In such a situation, it is crucial that the precipitation quickly drains away from the property. This applies all the more if the ground is dry or sealed, meaning that the water cannot seep away."

An old or blocked drainage system can then become a dangerous bottleneck. Homeowners should therefore regularly check whether the rain gutters are sufficiently dimensioned and in good condition. A water hose can be used to safely simulate how well the masses of water can be managed in an emergency and flow into the drainage system.

A non-return valve is important here to prevent the water from the sewer system from flowing back into the building. Here too, regular checks must be carried out to ensure that this flap is functioning as intended.

How to resist the water?

Norbert Gebbeken, President of the Bavarian Chamber of Civil Engineers, promotes the AWA principle when it comes to the risk of flooding: "Firstly, avoid, secondly, resist, thirdly, adapt", whereby "avoid" means not moving into areas where there could be problems in the first place.

In the case of existing buildings, some of which have only become susceptible to flooding as a result of climate change, owners are faced with a difficult decision, says Gebbeken: "You have to decide whether you want to resist the flooding or absorb it through adaptation."

The frequent weak points of basement doors and windows can be made pressure-tight so that no water can penetrate them. The foundations of the building must also be prepared in such a way that they cannot be undermined. It can be stabilized with piles or reinforced from the outside with reinforced concrete, and an enclosure with a dam is also possible. "It's all structurally feasible," assures Gebbeken.

If you want to build or rebuild in a potential flood zone, you have the alternative of allowing flooding by planning the building in such a way that the ingress of water only causes minimal damage. To do this, supply units such as electricity and heating must be installed on the higher floors. Finally, the walls must also be designed to withstand the water pressure.

Danger from the sun

Florian Becker from the Bauherren-Schutzbund points out that extreme rainfall is not the only effect of climate change that is causing problems for buildings: "There are a lot of dark components on houses that develop stress cracks or expand when exposed to intense sunlight. Sheet metal parts deform and gaps appear where water can penetrate."

Care should therefore be taken to ensure that expansion joints are correct and light-colored façade paints should be preferred. Heat-induced groundwater subsidence can cause the base plate of a building to shift. Generous planting with deciduous trees and minimizing the sealing of the property can help to mitigate the effects of climate change. Exterior sun protection and adequate ventilation relieve the strain on the building and also improve the quality of stay.

In view of the increasing impact of extreme weather, protection against natural hazards is a task that affects more than just individual homeowners, says insurance expert Anja Käfer-Rohrbach: "Without consistent adaptation to the effects of climate change, residential building insurance premiums could double in the next ten years due to climate change alone."