The foundation on clay soil


The condition of the soil is a very important factor. Depending on the composition of the substrate, the structure of the building may vary in strength. Accordingly, the foundation must be executed. One of the most common soils is the clay soil. How it relates to the foundation on clay soil, we have summarized in this guide.

Soil appraisal or expert advice on clay soil essential

To anticipate: this guide provides only a rough guide. In any case, a hydrogeological ground survey must be carried out for a foundation for a building. In the case of construction projects subject to approval, the soil survey has been legally required for several years. But even with smaller foundations on loamy soils, an expert should consult and possibly carry out a soil survey.

First, the following soils are distinguished:

  • cohesive soil
  • non-cohesive soil

Clay and loam soil

For example, a cohesive soil would be clay, non-cohesive soil would be gravel or gravel. The foundation on a non-cohesive ground undergoes a quick, but not too deep setting. On cohesive soil, however, setting can last even several decades. That's the case with a clay bottom. Even with a clay soil (ultimately also a clay soil), the settlement also takes several years.

Deep foundation and / or gravel filling

These are soils that justify deep foundation or gravel. The deep foundations under the actual foundation are guided so deep, until they "sit" on firm ground. If this is not possible, the gravel is alternatively used.

Why clay soil is problematic

The problem with clay soil is on the one hand the high density of the grains, which are separated by plenty of water. Even with a high load (or compression), it takes years for the water to be squeezed out. In addition, there are corresponding distortions, for example due to snowmelt in spring or very long-lasting rainfalls. Because even this leachate can only be derived conditionally or not at all.

Of course, it depends on the size of the construction project

Of course, a significant difference is whether you just want to make a foundation for a small, light garden house yourself, or if you want to build a multi-story, large building. For the garden house, a corresponding gravel can be made.

Enough alternative for leachate

But even this gravel pile should be adapted to the individual characteristics of the clay soil. Because the gravel pile not only ensures stability. It also provides leachate such as molten or rainwater with the ability to act as a sort of buffer. However, it is then crucial whether enough can be taken in with average amounts of leachate. The volume of the gravel filling must therefore be adapted to the local conditions.

Tips & Tricks

In addition, it is imperative to take into account that sufficient frost protection of the foundation can be ensured in such a case. All this speaks in favor of an expert.

Product Image: Ruud Morijn Photographer / Shutterstock


Video Board: Pro Tip: Building on Expansive Clay Soil