Table of contents:

Frost apron: function and structure at a glance
Frost apron: function and structure at a glance

Video: Frost apron: function and structure at a glance

Отличия серверных жестких дисков от десктопных
Video: What is frost? 2023, January
Anonim

Every foundation needs frost protection. Concrete floor slabs usually do not reach a frost-free depth, a frost apron does the job for them. Find out what constitutes a frost apron and how to put it into practice.

Table of contents Table of contents Frost apron: all-round protection for floor slabs

  • What is a frost apron and when do you need it?
  • How is the frost apron constructed?
  • Frost apron through foam glass gravel: how it works

Table of contents Table of contents Frost apron: all-round protection for floor slabs

  • What is a frost apron and when do you need it?
  • How is the frost apron constructed?
  • Frost apron through foam glass gravel: how it works

Water has a very special property - it expands when it freezes. And thereby develops forces that can even burst massive stones. If this happens with soil water under a foundation, it can literally be raised and then sag again after defrosting. Such a ups and downs don't last long, there is a risk of damage to the building. Frost protection is therefore essential. The risk of frost naturally varies depending on the region and geographical location, which is why the type of frost protection is determined by the respective house planner. If the floor is not at risk of frost, a substructure made of frost-proof gravel is sufficient as a substructure.

What is a frost apron and when do you need it?

A frost apron is needed to protect the floor from frost in buildings with a basement on flat concrete slabs, since these foundations usually do not reach the frost-free depth of 80 to 120 centimeters. Soils with a fine structure are particularly susceptible to frost, i.e. loamy, clay- and silt-free soils or fine sandy soils.

A frost apron is like a springform pan buried around the base plate from the kitchen, just made of concrete or reinforced concrete. However, the contactor does not run next to it, but as a circumferential ring below the base plate and can also take on static functions. A frost apron can also be insulated itself, but it does not have to be. As an alternative to the frost apron made of concrete, it can also be built from glass gravel - but under the entire floor slab and with a load-bearing function. The frost apron often also takes over the earthing and equipotential bonding of the building, in which case the foundation earth electrode is also cast in.

In any case, the frost apron ensures that the otherwise frost-exposed edge of the concrete slab is protected. The necessary depth of a frost apron depends on the actual risk of frost in the region, in areas at risk it extends to a frost-proof soil depth of 80 to 120 centimeters. The width of the frost apron and the specific thickness of the insulation material depend not only on possible static requirements but also on the risk of frost to be expected.

Whenever buildings or components in contact with the ground are insulated, one speaks of perimeter insulation, which is attached as a kind of outer skin outside and also below the building sealing. The requirements for such insulation are high, you can only use approved insulation materials. These must not absorb water, must be weatherproof and also very pressure-resistant if it runs under a building.

In addition to the frost apron, there is also the option of a frost screen, which does not have to reach a depth of 80 centimeters and is possible with thermal floor panels. You build a 60 to 100 centimeter wide, all-round layer of horizontally lying insulation panels, which are still covered with earth a good 30 centimeters thick. The frost screen runs outside the base plate. The area below the frost screen is kept frost-free by the rising geothermal energy and freezing is prevented. Foam glass gravel is also suitable as a frost screen, the transitions to the frost apron blur. With a frost screen, complete thermal insulation or a thermal bridge below the floor slab is possible. The effect of the screen is based on the fact that the rising floor heat is kept under the insulation, which keeps the floor and thus the edge of the floor slab frost-free.

How is the frost apron constructed?

There are various options for setting up the frost protection: If the floor is not at risk of frost, a ballast pack with a base plate that is otherwise insulated from below can be sufficient as protection so that no water collects under the foundation. With floors at risk of frost, nothing works without an apron.

Most frost aprons work as a kind of all-round strip foundation under the base plate and are built on a clean layer. In principle, you dig a surrounding trench and fill it with concrete or reinforced concrete. A common trench width is 40 centimeters, the frost apron and the cleanliness layer are then frost-free, often 90 centimeters deep. In this way, no soil water can penetrate under the floor slab and possibly collect under the concrete.

As an alternative to the foundation depth below the frost limit, there is the option of insulating the frost apron, which allows a shallow depth. The concrete strip is insulated on the side, the floor slab also from below.

The base plate can also stand on a so-called thermally separated strip foundation. The floor slab is completely insulated all around and also from below and only the bare strip foundation protrudes uninsulated into the floor. In this case, the weight of the building rests entirely on the insulation layer.

Another option for building a frost apron is foam glass gravel. It mainly consists of recycled glass, is pressure-resistant, heat-insulating, non-flammable, frost-resistant and has a high seepage capacity, so that it can also be used as a capillary-breaking layer that prevents rising moisture under a base plate. Strictly speaking, the glass ballast is an alternative to the frost apron and acts like a frost screen - a strip foundation is not necessary in most cases. If the groundwater level is high or the soil is loamy, drainage is necessary. Waste glass is not only available as ballast, but also as foam glass plates that can withstand even more pressure and are used on floors with standing or pressing water. So that the base plate is really frost-proof on the glass foam, the layer of gravel has to protrude all the way around a meter.

Schaumglasschotter
Schaumglasschotter

Foam glass gravel does not let water through to the components to be protected.

Photo: schamotte-shop.de

Frost apron through foam glass gravel: how it works

In practice, frost protection using foam glass gravel looks like this: After the construction pit has been excavated, the foundation earth electrode has been installed and other lines have been taken into account, geotextile fleece is rolled out on the leveled surface. This must protrude a good one meter laterally. Then pour the glass ballast in accordance with the planning specifications and compact it according to the manufacturer's instructions. The layer can measure 50 centimeters and more. The geotextile is turned over so that it is subsequently enclosed at all points of contact with the earth. Before pouring the base plate, a PE film or other geotextile is put on the gravel as protection.

Thomas Hess

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