Edition 19 April 2019, by Megan Janicke
Groundwater in the Netherlands has dropped to extremely low levels. Now, reports of sagging and sinking homes are flooding in from across the country. The Knowledge Center for the Approach to Foundation Problems (KCAF) usually receives one complaint of subsidence per week. However, since the dry summer of 2018, the organization has logged one or two complaints per day. Sometimes entire blocks of houses are impacted. The damage from subsidence ranges from jamming doors to cracks in walls and floors. A house can even become uninhabitable due to serious subsidence.
Damage greater than expected
KCAF has concluded that one in four houses built before 1970 is at risk. This amounts to approximately one million homes across the Netherlands.Low groundwater is primarily devastating for houses built on wooden posts. These posts must remain submerged in order to prevent rotting. However, experts say complaints are now coming in from regions not previously suffering from subsidence problems. Houses are beginning to sag in municipalities on rivers, such as the Betuwe, and those with a clay or sandy subsoil. “We did not expect reports from municipalities that are on sandy soil, because that is not a soil foundation typically associated with subsidence problems. But we now get such complaints much more often,” explains KCAF director Dick de Jong.
There are considerably more reports in regions with peat soil, such as the Groene Hart and southern Friesland. In these areas, the groundwater level is typically lowered artificially to keep polders accessible for tractors and cows. This causes the peat to dry out, resulting in faster subsidence.
What can be done for sinking homes?
The cost to rebuild an entire foundation is 50,000 to 60,000 euros for an average home and 100,000 euros or more for a larger house. Subsidence is caused by a long-lasting natural phenomenon and home insurance only compensates for damage caused by a sudden event, such as a storm or fire. Therefore, homeowners themselves bear the financial burden of this issue.
De Jong advises owners of homes with a subsidence problem to first contact their municipality. In some cases, the groundwater level may be raised and further complications can be prevented. There are also loans available to assist with foundation renewal expenses.
Buyers who are considering houses built before 1970 should get detailed information about the quality of the foundation. However, in-depth soil research is very expensive and is hardly ever done before a home purchase. KCAF has a ‘foundation viewer’ on its website which enables people to check soil conditions based on the postcode. The organization says this will also help educate estate agents and appraisers to make better assessments regarding foundations.
Confronting a 22-billion-euro problem
Two years ago, the Netherlands Environmental Assessment Agency (PBL) calculated that the damage caused by subsidence will amount to about €22 billion in 2050. The bulk of the cost is spent on restoring foundations of buildings in cities and rural areas.
De Jong thinks advises the government to consider whether measures should be taken at the national level. “That is also part of good climate policy,” he says. Drought isn’t solely to blame for subsidence. Natural gas and salt extraction, agriculture and even new construction projects can contribute.
Professor Ramon Hanssen of Delft University has contributed to a new soil subsidence map on behalf of the Netherlands Center for Geodesy and Geo-informatics (NCG). The map is based on data from radar satellites, changes in the network of the 250 GPS stations on buildings and gravity measurements. The utilization of satellite data enables the map to be constantly updated.
“We can track whether subsidence in Groningen will decrease due to the reduced gas extraction that the government has announced,” says Hanssen. He believes the Netherlands has reached a tipping point in water management. “We can continue to lower the groundwater and thus perhaps preserve the characteristic Dutch landscape with meadows, cows and windmills. But ever lower groundwater means enormous damage to buildings in historic cities,” he said in a recent interview with De Volkskrant. “Reducing this foundational damage can only be achieved by raising the groundwater level, which creates a more swampy landscape.”