Why foundation risk matters so much
Foundation problems are one of the most expensive hidden defects a home buyer can encounter. Repairing a failing foundation typically costs €30,000 to €100,000 — and in some cases more. Yet foundation risk is often overlooked during a viewing, because the problems only become visible once cracking is severe.
The Netherlands has a particularly vulnerable foundation landscape: large parts of the country sit on peat or clay soil, often far below sea level. This historically led to the use of wooden piles as foundations — and wood rots when it dries out.
The three main risk factors
1. Soil type
The soil condition determines which foundation type was used and how vulnerable it is:
- Peat soil: high risk. Peat subsides when it dries out and offers little load-bearing capacity. Areas: large parts of the Green Heart, North Holland, Utrecht.
- Clay soil: moderate risk. Clay has low load-bearing capacity and shrinks when it dries. Polder municipalities such as Haarlemmermeer, Rijnmond.
- Sandy soil: low risk of foundation problems, provided the piles are long enough to reach the load-bearing layer.
2. Construction year and foundation type
The construction year gives a strong indication of the foundation type used:
- Before 1940: mostly wooden piles or shallow strip foundations. Highest risk on peat soil.
- 1940–1970: mix of wooden piles and early concrete piles. Wooden piles from this period have been in service for 60–80 years and may be reaching the end of their service life.
- After 1970: predominantly concrete piles. Pile rot not applicable; risk of subsidence with poor execution or shallow foundation.
3. Drainage level and groundwater table
Wooden piles only rot when they periodically dry out. The drainage level — the difference between ground surface and groundwater table — determines this risk:
- More than 120 cm drainage: good, low chance of pile rot
- 60–120 cm drainage: moderate, attention needed for old wooden piles
- Less than 60 cm drainage: high risk, foundation survey strongly recommended
Free data sources you can consult
Basisregistratie Ondergrond (BRO)
The BRO contains soil survey data for the whole of the Netherlands. Via broloket.nl you can look up the soil type for an address for free. Note: the BRO sometimes has limited survey data for built-up areas.
Actueel Hoogtebestand Nederland (AHN)
The AHN gives the exact ground level in metres above sea level (NAP). Via ahn.nl you can view the elevation for any address. Combine this with the average groundwater level for your municipality (available via KNMI and water boards) for an indication of drainage.
Funderingsloket
The Knowledge Centre for Foundation Problems (KCAF) offers risk maps per municipality via funderingsloket.nl. Some municipalities have their own foundation risk maps available.
What does a professional foundation survey involve?
A certified foundation survey (following KCAF protocol) typically costs €700 to €1,500 and provides certainty about:
- The exact foundation type (wooden piles, concrete piles, shallow foundation)
- The condition of the piles (visual inspection via endoscope)
- The load-bearing capacity and a prognosis of remaining service life
For homes built before 1970 in peat areas, a foundation survey at purchase is strongly recommended.
How does PlotSense help?
The PlotSense Foundation Report (€35) gives a focused foundation risk assessment per address, based on construction year, soil composition, groundwater and the public FCAB map as a cross-check. For broader parcel information (cadastral boundaries, topography, setback distances) there's the Parcel Report (€25). More background on foundation risk and the FCAB map is on the Foundation Risk page.
This is an initial orientation, not a foundation survey. But it gives you a picture of the risk profile before the viewing — so you know whether to schedule a professional survey.
Address lookup is free. The Foundation Report is immediately downloadable for €35.