Heating systems used in everyday life have different technological capabilities and are distinguished by their efficiency. According to many indicators, today the first place in popularity is occupied by heating systems «warm floor». In many ways, this attitude to this method of heating is caused by the increased pace of small housing construction. Country houses, cottages and country houses are increasingly becoming objects of permanent residence. Against this background, the inhabitants and owners of such housing strive to achieve the most comfortable conditions in their apartments. Laying a water-heated floor is just fully capable of satisfying such aspirations.

Heating built into the floor is convenient in every way. In addition to the high efficiency of the method of space heating itself, such a system opens up wide possibilities for the design of the interior space of residential buildings. However, in order to achieve an acceptable temperature inside a residential building and make the heating equipment work optimally, it is necessary to follow the installation technology and correctly set the control mode.

Laying a water-heated floor is a sequential process in which each stage has its own meaning and sequence. The decisive stage of the whole work will be a properly made concrete screed for a warm water floor. What is the peculiarity of installing underfloor heating at home? On which element of the floor structure should you focus your attention?

Substrate for underfloor heating. What it is? What is the meaning of this element

The main condition for the successful operation of a home underfloor heating system is not only properly connected and configured equipment. In many ways, the heating efficiency depends on how competently the underfloor heating substrate is made, how the water heating circuits are laid, and finally, what kind of finishing floor covering is chosen.

Let you have the most powerful heating boiler, a pumping and mixing station with a mass of auxiliary devices and devices, a pipeline made of the most expensive pipes, just one detail can neutralize such advantages. Incorrect pipe laying, incorrectly selected water floor insulation will make even the most modern equipment ineffective. Precious heat will go to waste, giving only a small part of the floor surface.

On a note: the heat carrier circulating through the pipes of the water circuit must give up to 80% of its thermal energy to the floor surface, evenly heating the entire floor area in the heated room.

Such indicators are achieved by laying in the correct sequence a puff cake, in which there is a waterproofing layer and a substrate. This element of the puff cake is made of heat-insulating materials with low thermal conductivity. Due to this quality of heat-insulating materials, the necessary heat-reflecting effect is achieved. The heat, reflected from the substrate, rushes upwards with the main mass, transferring the optimal amount of calories to the floor surface. Underfloor heating with a water circuit hidden in a concrete screed or located in the middle of the flooring system becomes a key factor in the effectiveness of underfloor heating.

With this, we actually answered the question of why a substrate is needed. Thermal insulation is laid on a rough prepared surface, increasing the heat transfer of the water circuit towards the floor surface.

For reference: the substrate consists of a heat-insulating material, thus creating a “thermos effect”, and a waterproofing layer, due to which moisture penetration into the subfloor is prevented.

It is appropriate to recall here that water floors are usually mounted on concrete and wooden floors. A leak resulting from damage to the integrity of the heating pipe, the formation and accumulation of condensate can cause flooding of the basement and rooms of the lower floors.

For underfloor heating, the thickness of the substrate is important. The quality of a puff cake depends on the materials used in the construction. It will be optimal to use an insulating material for the substrate with the required rigidity and with the highest coefficient of thermal conductivity. It is important that the material be technologically advanced, i.e. convenient and practical to work with it. A good underlay will not be cheap, but it will serve for a long time and significantly increase the functionality of water floors.

The main quality characteristics in this case include the following aspects:

  • optimal parameters of hydro and thermal insulation;
  • the presence of high reflectivity;
  • environmental safety of the materials used;
  • high resistance to sudden temperature changes;
  • simplicity and practicality in installation;
  • high resistance to deformation;
  • fire resistance.

The listed parameters correspond to the ideal variant of the substrate equipment, however, in some cases, it is necessary to use materials with similar characteristics. The most common material that is used as a heater for a warm water floor is expanded polystyrene. This synthetic material is best suited in terms of its parameters for installing warm water floors in a country house, in a house or in a city apartment.

Basic materials for underfloor heating


And again we return to polystyrene foam. Why is this material most often used? What are its main features in the application process?

Traditionally, a warm water floor in most cases looks like this. A foam polystyrene substrate is mounted on the draft base, which is covered on top with a lavsan vapor barrier film and metal plates. Often, instead of plates, foil film is used. The main role played by metal plates or foil is the maximum and uniform transfer of thermal energy to the floor surface from the heating pipeline.

One of the lowest thermal conductivity coefficients should be attributed to the distinctive features of extruded (foamed) polystyrene foam. According to this parameter, judging by the data in the table, expanded polystyrene is second only to mineral wool.

Such material does not allow heat to escape into the subfloor, and due to interaction with the metal layer, ideal conditions are created for uniform heat distribution over the entire floor surface with maximum efficiency. The floor screed, laid on top of the entire structure, becomes a solid heating element with a large heating surface area.

Important! Expanded polystyrene is able to withstand heating temperatures up to 900C, so pipes can be laid directly on the substrate without fear of damaging the insulating material.


Usually, in a practical plane, they work with expanded polystyrene, the density of which is 25-35 kg / m3. Thick foam is used in the underlayment for floors on the first floors, which are located directly above the foundation or above the basement. Here a sheet or plate with a thickness of 100 mm is taken. In the absence of plates of the required thickness, the foam is laid in two layers (50mm + 50mm).

For interpanel floors, when installing warm water floors in a city apartment, polystyrene foam 20-30 mm thick is used.

Other materials used in the equipment of the substrate are:

  • foil materials;
  • cork coating;
  • mineral wool;
  • mineral mats;
  • fiberboard;
  • penofol.

The choice of one or another material is determined by the state of the base, on which the installation of the water circuit loop will be carried out in the future and the type of flooring. A water heated floor that provides heating of the internal space in a single room must have a substrate capable of performing two functions:

  • high reflectivity;
  • prevent the penetration of moisture into the subfloor in emergency situations.

It is appropriate to say that recently profiled mats, which are universal materials, are being used more and more often. Products have a heat-insulating layer and bosses, with the help of which it is convenient to quickly and accurately lay the loops of water circuits.

However, in this case, there are also disadvantages. The waterproofing properties of the substrate made of profiled mats leave much to be desired. Therefore, in such a situation, it is necessary to lay an additional waterproofing layer.

Important! During the laying process, it is worth remembering that the foil layer must go onto the walls in order to compensate for the thermal expansion of the screed.


Marking is applied to the substrate, in accordance with which the water pipe is laid. Here it is necessary to take into account the pipe laying step, which for underfloor heating should not exceed 30 cm.

Characteristics of substrate equipment materials

In some cases, the inhabitants of houses try to use for thermal insulation any materials that are at hand or have a low cost.

Consider the characteristics of the substrate made of various materials:

  • Polyethylene foil, self-adhesive — thickness 8 mm. It features high reflectivity, hydro and sound insulation.
  • Polyethylene one-sided, laminated — thickness 8 mm. It has good thermal insulation and water resistance.
  • Polyethylene foam (Tepofol) — only 2 mm thick. Average thermal insulation parameters;
  • Foil polystyrene of various thicknesses, with printed markings. High heat-insulating, hydro and soundproofing characteristics;
  • Tuplex backing, proprietary 3 mm thick. It has the maximum parameters of heat, hydro and sound insulation;
  • Underlay made of polystyrene and lavsan coated, 3 mm thick.

The smaller the thickness of the thermal insulation, the lower the thickness of the entire layer cake becomes. Accordingly, the height of the flows in the room is slightly reduced. The thickness of the screed over a water-heated floor can vary within 50-60 mm.

The listed materials are the set that is presented in the trading network today. The cost of materials may vary. Here, the amount of material used in the work and the intensity with which floor heating should be carried out are taken into account.

Less commonly used is cork, which is made from crushed oak bark. There is one important aspect here — such material is environmentally friendly. However, if moisture gets in, it can become a place for the development of the fungus. This material is supplied in rolls.

The cheapest option is foil polyethylene. Of all the materials listed, foil polyethylene is the most common today. Despite the fact that the material is characterized by a high degree of thermal insulation and fairly moderate waterproofing, foil polyethylene does not have sufficient rigidity and strength.

In order to achieve quality when installing underfloor heating, try to use foil polystyrene. Do not pay attention to the cost of the material, it is high, but the obvious benefits more than offset your costs, making the water floor durable and efficient.


The substrate is a structural element, without which it is impossible to do when laying warm water floors. Possessing the necessary layer of thermal insulation and waterproofing, the substrate provides a high rate of heating of the floor surface, reduces energy costs for heating a residential facility.


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