The construction of a floor slab


The construction of a floor slab: slab

Materials for floor tiles
  • Gravel, gravel or lean concrete
  • PVC or PE films
  • Polystyrene or PU for insulation
  • Spacer and reinforcement
  • concrete
  • dry bulk
  • screed
  • Flooring

Having "built on sand" is a proverbial existence threat. Whereby in reality this is quite manageable. Nevertheless, the construction of a floor slab must consider the conditions on site as well as possible and compensate if necessary.

The foundation carries the whole house along with everything in it as well as occurring wind and snow loads.

These loads must be removed into the soil, at the same time neither moisture nor cold from the ground into the building can penetrate.

Therefore, the planning and the careful construction of the floor slab is of great importance in house building. Unlike, for example, on the façade, hardly anything can be retrofitted on the base plate afterwards.

The soil is the basis

The construction of a floor slab: plate

The cost of a soil survey and a structural engineer are well invested.

Do you know exactly what the soil looks like on your site in the depths? Neither you nor your architect can really judge that.

Only a soil survey provides reliable information for the structural engineer, who then calculates what the optimal structure of the base plate looks like to avoid long-term damage.

If you want to save yourself these steps, you're basically playing some kind of Russian Roulette. With luck, things will be fine. If not, then definitely more costly and less effective, which is considered rescue measures.

The construction of a floor slab in the new building

The construction of a floor slab: construction

Insulation boards that can handle a high pressure load are needed.

For a new building is reasonably only a structure of the floor slab with insulation according to the passive house standard in question - just to prevent unwanted energy loss through the bottom plate relatively safe.

It is not a contradiction if you then take a version in which the underfloor heating is installed directly. Such Thermobodenplatten save the screed layer.

The graphics are the structure of a base plate without basement. It does not take into account additional measures, such as a frost apron and represents only a possible structure dar. Variants with more or less the same effectiveness, there is of course and it is also dependent on the materials used.

The construction of a floor slab: slab

Caution: In the construction, as shown in the diagram, the reinforcing steel reinforcement can only be fitted with plastic spacers on the insulation and the foil, as other spacers could otherwise injure the foil during concreting.

ice wall

Every floor plate must be protected against ground frost. Except for a few locations, this is common in our latitudes. A frost apron is a circumferential strip foundation that protects the bottom plate against ground frosts up to 80 cm depth.

Construction of a floor slab with foam glass ballast as insulation

The construction of a floor slab: slab

Whatever insulation is used should meet the passive house standard.

Gravel and insulation in one, that promises the use of foam glass ballast.

Whether this is actually an option and can be displayed in your house, must ultimately calculate the expert and judge.

Foam glass is definitely an interesting recycled material with good properties, such as a high compressive strength and can certainly be considered.

Often such innovations are not offered out of bluntness at all. Just ask.

Construction of the floor slab in the old building

In the old building, the bottom plate thickness is almost always less than it would be necessary by today's standards. Especially because the external insulation is missing - sometimes even the barrier against rising damp.

Mostly you do not know the structure of the floor slab in detail at all and can not easily find out more about it. There is usually no choice but to subsequently seal the old floor slab on the inside and to insulate it if you limit further damage as well as the loss of energy.

Does every house need a floor slab?

The construction of a floor slab: slab

Sheets made of PE or PVC ensure tightness.

Every house needs a foundation! This can be carried out as a strip foundation, base plate or as a combination of both. The latter is the most commonly used method, with the strip foundation in many cases forming only the outer border of the house. It serves in this case, the stability and also as a frost apron, to ensure frost protection down to the soil.

This method has proved to be successful because it is usually the most cost-effective and yet easy to manufacture variant. Compared to a pure strip foundation, in which under each masonry, the foundation must be turned, this is necessary with a circumferential strip foundation only under the outer walls. This can then be used simultaneously for shuttering the bottom plate.

For the sake of completeness: There are wooden houses that stand on supports on a ventilated floor structure, as they are common in the United States. It is basically a kind of pile construction.

Base plate - costs at a glance

The construction of a floor slab: floor

The supply lines are led through the bottom plate.

A normal base plate with a thickness of about 20 cm costs between 70 and 100 euros per square meter. For a thermo floor plate with integrated floor heating 130 to 150 euros per square meter are estimated. This is offset by the savings on screed work, as this is not needed. Even more expensive are strip foundations with the formwork per square meter, where less volume can come together, but not necessarily, if one considers the thinner concrete slab on it.

For a cellar, roughly another € 300 per square meter per square meter must be added (a floor slab is still needed).

Author: Christiane Baldwin - Online Editor and Handyman

Photo Credits:
  • Cover picture: Pixabay, stux
  • Excavator: Pixabay, AlexBanner
  • Insulation boards: amazon picture, baupark24
  • Graphic: Christiane Baldwin
  • Construction site: Pixabay, lucky2013
  • Slide: Pixabay, akilambe
  • Connections: Pixabay, distel2610
  • Post picture: Pixabay, annawaldl

Similar sites

  • Soapbox Construction Manual: Just build yourself
  • Scratching post construction manual
  • Construction manual for a modern LED candle arch
  • Floor construction
  • Build kennel yourself
  • Build a shoe rack yourself
  • Roof insulation: The optimally insulated roof
  • Seal bottom plate
  • Make Easter presents yourself
  • Build a lighted side table yourself: Free construction guide
  • Build wooden gazebo
  • Build a cat house yourself
  • Composter test: Westfalia thermo-composter 640 L
  • BluCave the clever storage system from Batavia in
  • Inexpensive 3D printer as a kit in the


Video Board: How to build an extension: part 3 concrete floor slab