Dig up a foundation


Many construction projects need a foundation on which to base them. What has to be considered when excavating a foundation and how you proceed can be read in detail below.

The different foundations

Many construction projects require a foundation. The foundation has different tasks depending on the individual requirements. This ranges from stability to even load distribution. There are three different foundations:

  • the dot foundation
  • the strip foundation
  • the plate foundation

The construction is similar for all three foundations, except that certain specifications with the size of the foundation are indispensable. This begins in any case with the excavation of the foundation.

The depth of excavating the foundation

For any foundation to be excavated, depth is a deciding factor. Because the foundation must be frost-proof. Otherwise, water may collect under the foundation.

Frost protection is important

If this water freezes, it can raise the foundation at certain points, so that the foundation (from a strip foundation) can break. Even with point foundations, a raised foundation can have a negative effect on the overall statics and stability of the building that is based on it.

For this reason, you must dig or excavate the foundation at least 80 cm deep. In particularly cold regions such as certain alpine valleys, the frost-proof foundation can even be between 1.20 and 1.50 m.

The dry layer or gravel layer

You may even want to dig up the foundation a little deeper, as a layer of gravel should be laid under it. At the point foundation this may still be missing, but not from a strip foundation.

The height of the gravel layer should start at 10 cm at the point foundation, at the strip foundation 10 to 20 cm and at the foundation plate even up to 50 cm. Gravel or gravel in grain size 16/32 is used. This is condensed.

This too is a measure for frost protection. The water on the one hand can run better and does not accumulate directly under the foundation. On the other hand, the water has enough room to expand when freezing, so that the foundation is not endangered.

The further construction in the excavated area

Not yet mandatory at the strip foundation, but at the latest with the plate foundation, a watertight film should be laid on the gravel layer. Then comes a steel mat as a reinforcement.

The lateral excavation of a foundation

Laterally, you may need to attach a formwork to excavate. Especially if the soil is loose or sandy. Then you can begin casting the foundations.

Tips & Tricks

Point foundations should be square and have dimensions between 20 x 20 and 50 x 50 cm. Strip foundations should have a minimum width of 20 to 30 cm.

Artikelbild: sima / Shutterstock


Video Board: How to do a foundation for a small extension