Technology of insulation of slab foundations. Insulation of a foundation slab: advantages of technology Insulation of a slab foundation

The Swedish slab is an insulated monolithic slab foundation of shallow depth. The main feature of this technology is that the entire foundation of the house is based on a layer of insulation (under the slab). Under a warm house, the soil does not freeze and does not heave. Such a foundation is suitable for any soil, at any depth of groundwater.

This technology is based on the basic principles of design and device shallow foundations on heaving soils described in Organization standard (STO 36554501-012-2008), developed by the Research, Design, Survey and Design-Technological Institute of Foundations and Underground Structures (NIIOSP) named after. N.M. Gersevanov (FSUE Scientific Research Center "Construction"), FSUE "Fundamentproekt", Moscow State University. M.V. Lomonosov (Faculty of Geology, Doctor of Technical Sciences L.N. Khrustalev) and the technical department of PENOPLEX SPb LLC.

The “Swedish slab” technology combines the construction of an insulated monolithic foundation slab and the possibility of laying communications, including a water floor heating system. An integrated approach allows you to quickly obtain an insulated base with built-in engineering systems and a flat floor, ready for laying tiles, laminate or other covering.

The main advantages of an insulated Swedish stove:

• The construction of the foundation and the laying of communications are carried out during one technological operation, which makes it possible to reduce construction time.
• The sanded surface of the foundation slab is ready for laying the floor covering;
• A layer of thermal insulation PENOPLEX FOUNDATION®, about 20 cm thick, reliably protects against heat loss, which means a significant reduction in home heating costs and an increase in the efficiency of the “warm floor” system;
• The soil under the insulated slab does not freeze, which minimizes the risk of frost heaving problems in foundation soils;
• Laying the foundation does not require heavy equipment or special engineering skills.

Installation features

To ensure normal operation of the insulated Swedish slab (USP) and prevent frost heaving, it is necessary to provide a groundwater drainage system (drainage system around the perimeter of the structure). An important role is also played by a non-heaving preparation device (a bed of coarse sand, crushed stone). If a combination of layers of crushed stone and sand is used, it is necessary to provide for the separation of these layers with geotextiles (when the fine fraction soil is located above the larger fraction). All necessary communications (water supply, electricity, sewerage, etc.) and inputs must be laid under the slab in advance.

The design of the Swedish slab involves the transfer of all loads from the structure (its own weight, operational loads, snow, etc.) to the insulation layer, which is why high strength requirements are imposed on the heat-insulating material used. The most rational option for use in this design is thermal insulation boards PENOPLEX FOUNDATION®, which have virtually zero water absorption and high compressive strength.

Instructions for use:

• Step 1. Removing the top layer of soil (usually about 30-40 cm);
• Step 2. Compacting sand and gravel preparation (coarse sand, crushed stone);
• Step 3. Installation of drainage around the perimeter of the structure and utility pipes;
• Step 4. Laying side elements and PENOPLEX FOUNDATION® slabs in the base;
• Step 5. Installation of the reinforcement cage on stands;
• Step 6. Laying pipes for the floor heating system, connecting them to the collector and pumping air into them;
• Step 7. Filling the monolithic slab with concrete mixture.

The heating system integrated into the foundation design ensures comfortable indoor conditions. And the use of durable and absolutely moisture-resistant PENOPLEX FOUNDATION® slabs as foundation preparation will significantly increase the thermal reliability and efficiency of the heated floor system. Ordinary water or antifreeze can be used as a coolant in the system (if in winter it is not possible to always maintain a positive temperature in the room). Almost all types of pipes can be used as heating pipelines in water heated floor systems: metal-plastic, copper, stainless steel, polybutane, polyethylene, etc.

When laying heating pipes, the following rules are followed:

• The higher thermal power of heated floors is achieved by denser pipe laying. And vice versa, that is, along the outer walls the heating pipes should be laid more densely than in the middle of the room.
• It makes no sense to lay pipes more densely than every 10 cm. More dense laying leads to a significant overuse of pipes, while the heat flow remains practically unchanged. In addition, a thermal bridge effect may occur when the coolant supply temperature becomes equal to the processing temperature.
• The distance between heating pipes should not be more than 25 cm to ensure uniform temperature distribution over the floor surface. To prevent the “temperature zebra” from being perceived by a person’s foot, the maximum temperature difference along the length of the foot should not exceed 4°C.
• The distance between heating pipes and external walls must be at least 15 cm.
• It is not recommended to lay heating circuits (loops) longer than 100 m. This leads to high hydraulic losses.
• Pipes cannot be laid at the junction of monolithic slabs. In such cases, it is necessary to place two separate contours on opposite sides of the joint. And pipes crossing the joint must be laid in metal sleeves 30 cm long.

Laying a shallow slab foundation during the construction of small buildings provides quite significant savings in materials and financial resources. However, seasonal freezing of the soil leads to movement and uneven rise and settlement of the laid slab, resulting in its deformation and subsequent destruction of the entire structure. Insulating the slab foundation by laying horizontal thermal insulation will help to avoid such risks, allowing you to cut off the zone of frost heaving of the soil under the structure.

Thermal insulation materials and methods of foundation insulation

Monolithic slab foundations find their priority application in the construction of one to three-story houses. It is a rigidly reinforced reinforced concrete structure that allows it to absorb large external loads along the entire load-bearing plane of the slab without deforming it. Since the depth of such a foundation is higher than the level of soil freezing, the forces of frost heaving in the soil must be compensated by insulating the foundation slab with heat-insulating materials even at the construction stage. The insulation must meet several basic requirements:

• not be subject to deformation under pressure;
• be resistant to moisture;
• have high heat-saving characteristics.

Mineral wool, previously used for such work, does not meet modern construction requirements due to the insufficient rigidity of its structure, high water absorption and relatively low thermal insulation qualities. The latest production technologies in the manufacture of thermal insulation materials provide a wide range of choice. Depending on the method of insulation of a monolithic foundation slab, the most popular are:

• polyurethane foam;
• Styrofoam;
• extruded polystyrene foam.

These synthetic polymer foam materials provide reliable protection for the sole of the monolithic slab from freezing. In addition, for shallow foundations, a foundation called an insulated Swedish slab is widely used, which is ideally suited for heaving soils. A brief overview of the properties of materials and installation methods will help you choose the right insulation for a monolithic foundation.

Polyurethane foam and its application

The main feature of this heat-insulating material is its dense closed cellular structure, filled with inert gases by 85-90% and ensuring its low thermal conductivity. To insulate foundations, the material can be used both in the form of finished sheets and in the form of liquid self-foaming two-component compositions, inflated by spraying.

The application of a liquid polyurethane foam composition to a concrete screed under the foundation slab being prepared compares favorably with the use of similar sheet materials.

1. High adhesion ensures strong adhesion to the surface without leaving gaps or cracks. But slab polyurethane foam requires pre-treatment of concrete with special compounds for reliable bonding.
2. When polymerized, the material forms a seamless coating that does not allow moisture to pass through. When using sheet polyurethane foam, additional waterproofing is required.
3. The composition is sprayed in 2-3 layers, which makes it possible to form any thickness of thermal insulation.

In addition, the environmental friendliness of the insulating material allows it to be used to insulate a finished foundation even indoors. But the main disadvantage of using polyurethane foam is the high cost of the components of the sprayed insulation and the unavailability of special equipment for doing work at home.

Polystyrene foam and extruded polystyrene foam

Extruded polystyrene foam is widely used for insulating a monolithic foundation slab due, first of all, to its affordability. Essentially, this is the same foam plastic, but the difference in manufacturing technologies determined their different properties and thermal insulation characteristics.

The main advantage of extruded polystyrene foam is that, with a low specific gravity, it has high compressive strength. This property allows it to withstand significant static loads without undergoing deformation, and the porous structure of gas-filled closed cells determines its low thermal conductivity.

An undoubted advantage over polystyrene foam is the ability of extruded polystyrene foam to be minimally saturated with moisture, practically not allowing it to pass through. Polystyrene foam, due to its structure, has high water absorption, which is why it quickly loses its heat-insulating properties and becomes unusable, so its use as insulation for a foundation slab is undesirable.

Features of insulating a slab foundation with polystyrene foam

Extruded polystyrene foam (EPS) is produced in the form of finished sheet material under different brands and, accordingly, in different thicknesses. To reliably insulate a foundation slab, it is necessary to first make a calculation by determining the required thickness, taking into account the density of a specific grade of EPS, the thermal resistance of the concrete slab being laid, as well as the climatic region. It is better to leave this task to specialists or use the instructions of SNiP on construction heating engineering and thermal protection of buildings.

Calculating the thickness of thermal insulation materials when insulating a slab foundation is a fundamental factor in constructing a high-quality foundation for a building under construction!

Laying of sheets of expanded polystyrene is carried out on waterproofing, which is used as bitumen roll materials. The sheets are glued end-to-end to each other on a surface preheated to the required temperature. For waterproofing materials that do not have a bitumen coating, an adhesive composition with special mastics is additionally applied. It should be taken into account that they should not contain various types of solvents, otherwise it will not be possible to avoid melting the polystyrene foam sheets.

Some manufacturers produce EPS boards that have a locking connection, which simplifies their installation and ensures minimal gaps between them. This insulation design helps reduce heat losses and eliminates the so-called “cold bridges”.

Before pouring a monolithic slab, the laid insulation will need to be protected from contact with the components of the liquid concrete solution. When reinforcing the foundation with a bonded iron frame, it will be sufficient to use a polyethylene film 150-200 microns thick, which is laid in one overlapping layer with an overlap of 100-150 mm and secured with double-sided tape. If welding work is required to install the reinforcement, it is recommended to protect the laid heat-insulating material with a cement-sand screed or low-grade concrete.

Construction of the foundation “insulated Swedish slab”

One of the fairly common options for insulating a shallow slab foundation is the method of combining building communication systems in a monolithic structure being constructed. Heating, water supply and sewage pipes passing through the slab additionally heat the slab and soil, preventing them from undergoing uneven deformations. Such structures are indispensable on complex heaving soils, as well as on peat bogs with a high moisture content.

To avoid direct contact with the ground, additional insulation of the “Swedish plate” is carried out using extruded polystyrene foam sheets. In this way, the thickness of concrete in the foundation monolith is reduced by almost 2 times.

The technology for constructing a slab foundation using the “insulated Swedish slab” type consists of several stages:

• clearing a shallow pit;
• laying of geotextile fabric;
• adding a sand cushion followed by layer-by-layer compaction;
• laying insulation;
• tying the reinforcement cage over the entire area of ​​the slab;
• installation of communication pipes;
• pouring concrete into the prepared area.

The main advantage of this insulation method is the combination of technological operations for installing a slab foundation with the simultaneous laying of communications, which can significantly reduce construction time. In addition, the ease of erection of the structure does not require the involvement of heavy construction equipment at the site.

Careful adherence to technological standards, as well as rules and methods for insulating shallow monolithic slabs in various climatic zones, allows the construction of foundations for low-rise buildings on almost any soil.

The slab base can withstand significant external influences and is suitable for construction in areas with complex, unstable soils, prone to frost heaving, and high groundwater levels. Insulating the foundation slab will help to significantly reduce heat loss through the base and reduce the impact of frost heaving of the soil. When the soil moves, the building rises and falls along with the foundation, which protects the house structure from the formation of cracks.

general information

The design of the slab base consists of layers:

• geotextile is covered with overlapping strips on the sand layer, the joints are taped;
• pour crushed stone in a layer of 15-20 cm;
• pour a leveling layer of cement mortar, 5-10 cm thick;
• be sure to isolate the structure from moisture using rolled or coating materials;
• arrange a heat-saving layer;
• cover with plastic film in stripes overlapping by 20 cm;
• lay the reinforcing mesh;
• poured with concrete.

Installation and insulation of a slab monolithic foundation is expensive due to the high consumption of building materials. When the soil freezes to a great depth and a significant deepening of the strip foundation is required, installing a slab will be cheaper and less excavation work will be required.

Advantages of a slab foundation

The slab base has the following advantages:

• the concrete slab serves as the floor of the first floor, which further reduces the cost of its installation;
• is an excellent option for the foundation of a house, the construction of which is carried out on floating soils; the slab and the entire house along with it move simultaneously with the soil;
• the slab can be mounted on any type of soil, even on peat bogs and marshy areas;
• the slab is erected above the soil freezing level, thanks to the sand cushion, frost heaving has virtually no effect on the structure;
• reinforced concrete slab is not subject to shrinkage;
• suitable for the construction of buildings up to 3 floors.

Insulating the foundation slab reliably protects it from deformation during seasonal soil heaving and extends the life of the structure.

Advantages of slab insulation

Polystyrene foam, polystyrene foam, and polyurethane foam are used as thermal insulation materials. Mineral wool is not suitable due to its low strength and high degree of moisture absorption.

There is a technology for installing a Swedish stove. The main difference is that the concrete structure is built on a layer of heat-saving material, thanks to which the soil under the house does not freeze or heave.

The main advantages of the Swedish stove are:

• the construction of the foundation and the laying of communications are carried out in one technological cycle;
• the heat-saving layer allows you to increase the efficiency of the heated floor;
• installation of the foundation is carried out without the involvement of a large amount of construction equipment.

A drainage system consisting of pipes for draining rain and melt water is provided around the building.

The design of the slab helps to transfer all the loads from the building to the layer of heat-saving material, therefore increased demands are placed on the materials used.

Disadvantages of a slab foundation

A slab foundation is not always the best option. You should always perform all the necessary calculations in advance and select the most suitable type of foundation for your home.

Disadvantages of the stove:

• not suitable for construction on sloped areas;
• to build a house with a basement on a slab, you need to dig it to a great depth, this will be very expensive;
• it is difficult to repair communications carried out under the foundation slab;
• During construction in winter, additional costs will be required for heating the concrete and maintaining the required temperature on the site.

A slab foundation is erected only when it is impossible to install a strip foundation.

Insulation materials

The table shows the materials used to insulate the foundation slab and their characteristics:

Most often, extruded polystyrene foam is used as insulation under the foundation slab.

Installation of insulated slab

The construction of a monolithic slab foundation requires performing all calculations taking into account geological, climatic conditions and the mass of the building.

Insulating a slab foundation allows you to save significant money on heating the room during operation.

Site preparation

At the creation stage of the project, it is necessary to take into account that the area for the foundation slab must be wider than the house building by at least 1 m on each side.

Instructions for performing preparatory work:

1. The site where construction is taking place is cleared of debris and the root system of trees and shrubs.
2. Mark the position of the slab according to the design.
3. The fertile layer of soil is cleared and removed. The degree of slab burial depends on geological and climatic conditions. Most often, the thickness of the slab varies from 20 to 30 cm, less often the base is buried by 50 cm.
4. They dig a pit and manually level its bottom and side walls.
5. Pipes are installed around the perimeter to drain rain and melt water.
6. Geotextiles are laid out in overlapping strips. The material should cover the bottom and extend to the entire height of the walls.
7. Drive in wooden stakes or metal rods. Pull the cord strictly horizontally. It will serve as a guide for uniform filling of sand and crushed stone.
8. Pour sand 20-30 cm thick. Distribute the sand evenly over the entire area, moisten it with water and compact it well.
9. Lay out geotextiles.
10. Pour crushed stone, distribute it evenly around the perimeter, and compact it thoroughly.
11. Conduct all necessary communications. They dig trenches under them in the rubble a little wider than the cross-section of the pipes. The pipeline is laid and a layer of sand is poured on top.
12. The sandy surface is leveled.

If the pipeline is laid before the crushed stone compaction stage, the pipes may crack.

Insulation of the slab

Step-by-step instructions for insulating a monolithic foundation slab:

1. They install removable formwork from boards and install supports so that the structure does not fall apart under the weight of concrete.
2. A layer of concrete 50 mm thick is poured.
3. After the cement mortar has completely hardened, sheets of penoplex are laid on it close to each other and glued. The adhesive composition is applied in dots along the perimeter of the sheet and in the center. A layer thickness of 10-20 cm is sufficient. The joints of the row are placed in a checkerboard pattern, offset by 1/3. When laying in two rows, the joints should not intersect.
4. Spread thick polyethylene in overlapping strips. The joints are sealed with tape.
5. The reinforcement frame is laid and the formwork is filled with concrete.

After the slab has dried, the formwork is dismantled, the side walls are thermally insulated with the same material that was used to lay it under the slab.

The insulated base helps to increase heat saving indoors.

When installing insulation on bitumen insulation, you need to wait until it dries completely. If laid on a damp layer, the materials may be damaged and the effect of thermal insulation and waterproofing will be reduced.

Rules for installing heating pipes

When installing USHP, heating pipes are used. There are the following rules for their installation:

• More dense pipe laying allows for higher room heating temperatures.
• The distance between external walls and pipes should not exceed 150 mm. Closer to the center, the laying step can be increased to 250 mm.
• To minimize hydraulic losses, the length of one loop should not exceed 100 m.
• Do not lay pipes closer than 100 mm from each other.

Heating pipes must not be installed at the junction of monolithic slabs. In this case, it is better to lay two circuits. The pipeline crossing the joint is insulated with steel sleeves 30 cm long.

How to make an insulated Swedish stove with your own hands can be seen in the video:

An insulated foundation slab allows you to reduce heating costs during operation and helps reduce the level of frost heaving in the soil. Thanks to this, the life of the foundation is extended, and living in the house becomes more comfortable.

It is difficult to build a solid foundation on unstable soils. In such cases, a slab base is used. It acts as a shallow foundation, drifting across the site as soil masses move. Since the entire structure moves, no destructive stresses arise.

For proper operation of this type of foundation, it must be protected from freezing. Insulation of a monolithic foundation slab:

• prevents destruction of concrete from temperature changes;
• contributes to the warm floor of the first floor;
• makes it possible to save on heating the building;
• reduces the heaving of the soil under the building.

Choice of insulation

Not every material, even the most effective one, is suitable for working in or near the ground. When choosing a material you need to be guided by:

• moisture-proof. When saturated with water from the soil, the product loses its insulating properties. Expanding when freezing, moisture violates the integrity of the coating, nullifying all work;
• strength. Seasonal movements of soil masses create noticeable pressure on the material. It is especially noticeable on rocky soils. Sharp edges can push through the product, leaving cracks or breaks in it;
• resistance to aggressive environments. Soils are often chemically and biologically active. Groundwater may contain increased concentrations of salts. All these factors lead to premature destruction of the insulation.

When installing insulation inside a building, the material must be non-flammable. If there is a possibility of fire, no harmful substances should be released that could cause suffocation.

With all this, the service life of the insulation must be no less than the service life of the finishing material. In this case, you will not have to change it before the coating becomes outdated. Otherwise, you will have to dismantle the finishing fabric that still complies with the standards.

Often, extruded polystyrene foam is used for zero-cycle work. Insulating the foundation slab with expanded polystyrene, done according to all the rules, allows you not to worry about the safety of concrete and heat conservation.

Characteristics of expanded polystyrene

Expanded polystyrene is used for thermal insulation of the foundation slab:

• outside;
• from the inside;
• in the body of concrete

External insulation technology

The height of the slab can be from half a meter. Freezing around the perimeter is the most dangerous for the foundation. Therefore, basically, insulation is attached precisely to the side surfaces.

Before covering the foundation with a layer of insulation, it must be waterproofed. Even though polystyrene foam is waterproof, its coating is not seamless. Moisture penetrates into the seams between the slabs, which can destroy the slab.

Waterproofing occurs by applying bitumen mastic or melting paraffin on the surface and edges of the slab. The second method is more economical and reliable. Using a gas burner, pieces of paraffin are melted. The material is evenly distributed over the surface, absorbing into it.

Waxing closes the pores of concrete, creating a barrier against moisture. Complete adhesion helps prevent insulation peeling. This means that insulation can be easily attached to it.

Expanded polystyrene boards are mounted with glue or cement-sand mortar. The first option allows for insulation at sub-zero temperatures. The underground part is secured only by gluing. This is necessary to avoid violation of the hydraulic barrier.

The base part of the insulation of the slab foundation with polystyrene foam is additionally fixed with plastic dowels. To do this, holes are drilled through the glued plates. They go through all the insulation and part of the foundation.

The glue is applied around the perimeter of the slab and in several stripes in the center. Wait for 1 minute and press the plate against the surface for a couple of minutes. After gluing, the bottom plates are sprinkled with a layer of sand. This helps secure them in the mounting position.

The second row of insulation is installed with offset seams. It is advisable to bandage the horizontal joints as well. This helps to avoid the occurrence of cold bridges.

If the thickness of the slabs is not enough, insulation is carried out in two layers. Products with maximum thicknesses are taken to avoid installation of several layers. The slabs of the top layer must overlap the seams of the lower ones.

Fixation with umbrellas is carried out at five points on the slab. The dowels are installed after the slabs are completely glued, but no later than three days later.

After installation, the seams are sealed with foam. Excess foam is cut off and the surface is plastered over a mesh. The mesh is necessary for better adhesion of polystyrene foam and plaster.

Internal insulation technology

When insulating a monolithic foundation slab from the inside, the material is laid in two ways:

• On top of the stove;
• In the body of concrete.

With the first method, the sequence of work is as follows:

• waterproofing is installed along the foundation slab, extending onto the wall;
• logs are screwed on top of the waterproofing layer;
• a layer of insulation is placed between the logs;
• a waterproofing film is attached to the joists on top of the insulation;
• a plank base, plywood or OSB boards are mounted on the film;
• A backing made of cork, foamed polyethylene or pine needles is laid on top of the subfloor. The finishing floor is mounted on it.

You can do without lag. In this case, the slab foundation is completely insulated with polystyrene foam. The material is laid in a continuous layer. The underlay and finishing floor covering are laid immediately on top of it.

When installing in concrete, the following work is performed:

• the base plate is waterproofed;
• An insulation layer with a thickness of at least 100 mm is installed. It is better to use products with a locking connection system;
• PVC film with a density of at least 1.42 g/cm3 is laid on the insulation;
• reinforcement mesh is laid. Its role can be played by a masonry mesh with a cell of 100*100 mm;
• the surface is filled with a screed no thinner than 5 cm;
• The finishing coating is laid over the screed.

For internal insulation, only self-extinguishing polystyrene foam should be used. For installation under a screed, products of flammability class G4 can be used.

Insulation of the foundation slab body

Warm concrete is used in many areas of construction. It can be purchased in the form of a ready-made mixture or manufactured at the construction site. For preparation, granulated polystyrene foam is added to the initial mixture to form the foundation slab.

Polystyrene concrete with a density of D1200 is used for constructing structural elements. When preparing 1 cube, the composition includes:

• 300 kg of cement M400;
• 1.1 m3 of polystyrene foam granules. It is better to use granular rather than crushed material. It has the shape of a ball, which leads to better envelopment with the cement mixture;
• 800 kg of sand;
• PAD. Often, saponified resin is added. Its presence in the composition ensures better adhesion and increases heat-shielding properties.

When creating such concrete, you need to remember about shrinkage. It is 1 mm per 1 m of surface. The slab needs to stand for some time after gaining strength. It is necessary to arrange a leveling screed on the surface.

The flammability class of such a product is G1. The concrete itself does not burn, but the insulation granules are exposed to fire. As a result, pores are created in the body of the foundation slab. They reduce the density of the structure and increase its moisture absorption.

The thermal conductivity of such a slab will be approximately 0.105 W/(m*C). The product requires additional insulation of the slab foundation from below. The thickness of the insulating material will be less, unlike plain concrete.

The choice of type and technology for insulating the foundation slab depends on the design features of the building and the construction site. Choosing the optimal solution is based on data from thermal engineering calculations and comparison of estimated costs.

The purpose of this article is to go beyond the scope of this project and tell, on behalf of specialists, the basic rules for working with the material that can be useful to everyone.

When constructing this type of foundation, extruded polystyrene foam (EPS) was used. In a master class format, professional builders will tell you how to choose and how to properly work with extruded polystyrene foam when insulating various types of foundations. Namely:

• Why is it necessary to insulate the foundation?
• What to look for when choosing a material for foundation insulation.
• How to properly secure extruded polystyrene foam to the foundation.
• What tool is needed for the job?

Why is it necessary to insulate the foundation?

The foundation is the underground part of the structure that transfers the load from the overlying structures to the prepared soil foundation. Foundations are of the following types:

• Slab, shallow, with spatial reinforcement. This gives the structure rigidity and allows it to withstand loads arising from uneven soil movement without internal deformation.

• Tape - laid below the freezing depth, etc. MZLF is a shallow strip foundation, with a base depth above the calculated level of seasonal soil freezing.

• . Insulated Swedish Plate. This foundation is a monolithic concrete slab mounted on a base insulated with extruded polystyrene foam. A water underfloor heating system and all utilities are integrated into the foundation.

This type of foundation is considered the most technologically advanced and energy efficient. One system combines the foundation and a low-temperature heating system, eliminating the formation of local overheated zones and providing comfortable radiant heat. In addition, the foundation is not exposed to the forces of frost heaving, because Anti-heaving measures have been carried out. Namely, the heaving soil was excavated and replaced with non-heaving soil (sand or crushed stone), a drainage system was installed, the blind area and the base of the slab were insulated.

Up to 20% of the total heat loss of the building occurs through the foundation.

Kogut Andrey TechnoNIKOL technical specialist

To achieve maximum energy efficiency of a building, it is necessary to create a closed insulated loop. This means that, in addition to the main structures, such as walls, roof and basement, it is also necessary to thermally insulate the foundation.

In some cases, it is enough to insulate the floor and basement, but when organizing a used basement thermal insulation of foundation walls is a prerequisite to achieve the required level of comfort and reduce heat loss.

In shallow strip and slab foundations, thermal insulation can reduce the effect of frost heaving. Soil heaving is formed due to the freezing of water in the soil and its subsequent expansion. Different soils have different degrees of heaving. For example, sands allow water to pass through them well, and it does not linger in them. Clay, on the contrary, does not allow water to escape, and due to the presence of a large number of small pores, it has a high capillary suction of moisture. Improper design on heaving soils can lead to serious consequences, including destruction of the foundation. If you leave the foundation uninsulated, the heat flow will go down and warm the soil, protecting it from freezing. However, the house may not be heated constantly, and in this case the soil heaves. Thermal insulation of the foundation and blind area is one of the measures to combat frost heaving.

Basic principles for choosing thermal insulation for foundation insulation

So, summarizing all of the above, we conclude: the foundation needs to be insulated. Not every insulation is suitable for this, but only a material that can work in aggressive environmental conditions. Those. thermal insulation designed to be “non-removable” must be moisture resistant, have a long service life during which it will not lose its thermal insulation properties, and have strength sufficient to withstand the load from the overlying structures.

Kogut Andrey

Extruded polystyrene foam (EPS) has a low thermal conductivity coefficient of 0.028 W/(m*°C) and a minimum water absorption coefficient of 0.2% by volume. The insulation does not absorb water, is chemically resistant and does not rot. Compressive strength at 2% linear deformation – no less than 150 kPa (~ 15 t/sq. m) and higher. Service life in soils is at least 50 years.

High compressive strength allows the use of EPS in loaded structures (foundations) and ensures the stability of the thermal insulation thickness under load.

The thickness of the thermal insulation layer should be taken based on calculations based on several conditions:

• Purpose of the building (residential, administrative, industrial, etc.).
• The insulation must provide the required heat transfer resistance for a given type of building.
• There should be no seasonal moisture accumulation in the structure.

Calculation thickness of thermal insulation for the foundation is made according to the methodology set out in SP50.13330.2012 “Thermal protection of buildings”. For different regions, the thickness of thermal insulation may vary, depending on climatic conditions. It should also be taken into account that increasing the thickness of thermal insulation increases the energy efficiency of the building and, therefore, leads to lower heating costs.

When choosing technical characteristics of thermal insulation, we are guided by the following principles:

1. When thermally insulating a strip foundation, when only the vertical wall is insulated, increased strength of the material is not required, because in this case, the EPS takes up loads only from the backfill soil. Therefore, for shallow foundations, brands of extruded polystyrene foam with a compressive strength (at 10% linear deformation) of 150-250 kPa are suitable.
2. When laying EPS slabs under the base of the foundation or under the slab, the loads on it increase significantly, and accordingly, the requirements for its strength increase. In this case, it is recommended to use thermal insulation boards with a compressive strength of 250 - 400 kPa.
3. A material has been developed specifically for USP with a compressive strength at 10% deformation of 400 kPa and increased slab sizes to increase installation speed. In addition, the increased dimensions of the slabs make it possible to reduce the number of seams and, accordingly, increase the uniformity of the layer.

The nuances of installing extruded polystyrene foam when insulating the foundation

Insulation of the EPPS foundation, depending on its design, should be divided into a number of sequential steps:

• Preparing the base. When insulating an EPS strip foundation, the walls must be smooth, free of dirt and concrete deposits. If necessary, we remove uneven surfaces and cover up sinkholes, chips, etc. cement-sand mortar.

• Choosing a method of fastening EPS. To attach the insulation, we use polymer-cement mixtures or, to speed up installation, special polyurethane adhesive foam.

• Adhesive foam is applied in a strip approximately 3 cm thick along the entire perimeter of the slab, as well as in one strip in the center of the insulation.

• The distance of the adhesive foam strip from the edge of the slab is at least 2 cm.

• Before installing the slab, wait 5-10 minutes and only then glue it to the foundation wall.

• We foam the gaps between the plates (if they exceed 2 mm).

• If mechanical fixation of thermal insulation is provided, then the number of dowels is calculated as follows - for fastening 1 sq. m of thermal insulation on the central part of the foundation requires 5 pieces. fasteners We fix the EPS on the corner parts of the foundation at the rate of 6-8 dowels per 1 sq. m.

• When insulating the base of a strip foundation or monolithic slab foundation, EPS is laid loosely on a prepared base (usually on a compacted sand bed). In this case, it is enough to foam the seams with adhesive foam and, if necessary, fasten adjacent thermal insulation boards together. You can use a nail plate for this.

In this case, special fasteners can be used, which are a spike with teeth for fixation in the material and a flat platform with an adhesive layer.

Together with similar fasteners, gluing is done using adhesive foam for polystyrene foam or to a special adhesive mastic that does not contain solvents. If necessary, the seams are sealed with mounting or adhesive foam.

The layout of EPS slabs during the construction of USHP is carried out as follows. We lay the first layer on the prepared base - a compacted sand cushion - with the seams staggered relative to the adjacent slabs. The side elements are “L” blocks, which are two EPS slabs connected perpendicular to each other.

As a rule, such elements are made by installing formwork, but it is possible to use ready-made elements that do not require the use of formwork. Such “L” blocks can be manufactured in a factory, or they can be assembled independently at the work site. For this purpose, a special corner fastener has been developed, which consists of corners and screws, and which are mounted at a distance of 300 mm from each other. All elements of corner fasteners are made of high-strength polyamide, which eliminates the formation of cold bridges.

Summarizing

In addition to increasing the energy efficiency of the foundation, EPS insulation increases its service life, because the waterproofing is reliably protected by durable material from various mechanical influences. By choosing the option of permanent formwork made from extruded polystyrene foam, you can significantly speed up and simplify all work on the construction of the foundation, because there will be no need to assemble and further disassemble wooden formwork, which means the developer will save time and money.