Foundation problems

The majority of owners in areas with a low groundwater level have to take into account an uninsured damage amount of between 500 and 10,000 euros. This is the conclusion of a study by the Deltares research institute, commissioned by the Dutch Association of Insurers. The Association argues for follow-up research into preventive measures against the damage, the costs thereof and the identification of other interests. Based on the results, political choices must be made in terms of water level, land development and available budgets.

Groundwater level up

For shallow foundations that rest on soft soil layers, such as peat and clay soil, the total damage up to 2050 in the Netherlands amounts to a maximum of 39 billion euros. Due to an increase in drought due to climate change, this amount can increase by up to 15 billion euros. Insurers do not cover damage to the foundations of a house due to drought, because it is not an 'uncertain event'. After all, the damage caused by years of low groundwater levels is not an unforeseen event. That is why the Dutch Association of Insurers is calling on the water boards and local authorities to permanently raise the groundwater level, which can limit further damage. The Association realises that this is not possible everywhere, because local flooding can occur. In such situations, other solutions will have to be found.

Thorough research needed

Due to economies of scale, agricultural companies and their suppliers have started to use increasingly larger and heavier agricultural machinery over the years. The groundwater level is purposely kept low to provide dry and firm soil that can support these heavy machinery.

In addition, in urban areas, the soil can subside due to the weight of the buildings. To prevent local flooding, the water level is kept low, which in turn causes soil to settle. In mostly outdated residential areas, the repair of foundations and home damage will lead to enormous costs, on top of the investments for sustainability. That is why there must be a clear trade-off between the costs of repairs, preventing additional damage to the 1 million homes and a different layout of the environment. The coherence with nature policy, agricultural interests, opportunities in energy transition and urban renewal should also be taken into account.

The Association will therefore enter into discussions with stakeholder organisations to set up a thorough investigation that should form the basis for a proper consideration of the various interests.

Pile rot and shallow foundations

In the Netherlands, wooden pile foundations were used for centuries until around 1970. The load-bearing function of this remained fine because the wooden pile remained in good condition under the groundwater. Now that the groundwater level has been dropping for years, oxygen is getting to the wood and pile rot is occurring. If a wooden post is dry for ten to fifteen years, the wooden post no longer has sufficient load-bearing capacity because the top has deteriorated too far. Well-known areas where pile rot occurs are South and North Holland. In municipalities such as Rotterdam and Amsterdam, the problem has been known and researched for decades. However, the damage caused by subsidence of shallow foundations due to a low groundwater level is much less well known. This type of foundation rests with a wide masonry base or concrete slab on a ground layer below ground level. If this soil layer dries out due to a low groundwater level, the foundation subsides and damage to homes occurs.