What is an insulated Swedish slab foundation? How does a Swedish slab foundation work and what are its advantages? During the marking process, it is determined

At the initial stage of building construction, the foundation is laid. The foundation is subject to not only requirements to ensure the stability and durability of the building. It is important to reduce the cost of maintaining a comfortable room temperature due to the energy efficiency of the foundation structure. The insulated Swedish stove meets the specified criteria. It represents a solid reinforced concrete base that combines heated floors and utilities. Let us dwell on the design features and manufacturing technology.

Swedish slab foundation - purpose and scope

When thinking about the design of the foundation, most developers choose between strip, slab and pile structures. However, modern construction methods and innovative technologies make it possible to build a fundamentally new foundation. The Swedish slab is a shallow slab-type base made of concrete and reinforced with a reinforcement frame.

The Swedish foundation slab is a multi-layer structure. The construction in the form of a kind of sandwich allows you to speed up the construction cycle and solve a number of important problems:

Insulated Swedish slab (USP) - a modern and complex foundation design

effectively insulate a monolithic foundation slab;
arrange electrical cables, water pipes and sewer networks;
prevent possible deformation of the base;
maintain a comfortable room temperature by heating the floor;
create a reliable base for laying decorative coverings.

A foundation slab with an integrated heating system is used for the construction of buildings on soils containing an increased concentration of sand particles, peat, and clay inclusions.

The design features and safety margin of a monolithic slab allow the construction of buildings of various types:

log buildings;
timber houses;
frame buildings;
panel houses;
buildings made of bricks and porous concrete blocks.

The use of lightweight building materials makes it possible to erect buildings on a warm slab, the maximum number of floors of which is 3 floors. The Swedish slab is constructed after performing thermal engineering calculations, as well as design measures that take into account the load from the mass of the structure and the characteristics of the soil. It is important to choose the right building materials from which the walls, ceiling and floor are built. Electrical appliances together with internal communications are placed in accordance with the design documentation.

The main feature of this technology is that the entire foundation of the house is based on a layer of insulation (under the slab)

A warm foundation in the form of a slab is a complex structure, the construction of which is associated with increased costs. When deciding to build an insulated Swedish USHP slab using modern insulation, you should carefully evaluate all factors.

Multilayer construction is preferred in certain cases:

when the construction site is located on problematic soils;
during the construction of buildings with a box height of up to 10 m;
when located near the zero groundwater level.

The decision to use an insulated Swedish slab as the foundation of a building is made individually after analyzing all factors.

Insulated Swedish stove - main advantages and weaknesses

The experience of using slab foundations in Sweden confirms that the Swedish warm slab combines innovative technical solutions aimed at energy saving. USP plate is widely used abroad and is gradually being introduced by our builders.

A characteristic feature of the Swedish slab technology is that Swedish manufacturers have already calculated all sorts of foundation construction options for this technology, depending on the type of soil.

The number of supporters of the new fundamental framework is constantly increasing due to its advantages:

reduced duration of construction activities. The necessary utilities are laid simultaneously with the construction of the foundation;
no unevenness on the concrete surface. Sanding the subfloor at the final stage of construction allows you to lay the floor covering on the concrete;
preventing soil deformation under the foundation during freezing. A thermally insulated foundation minimizes the likelihood of soil deformation at subzero temperatures;
the possibility of constructing an insulated base without the use of special equipment. Eliminating the need to use lifting devices reduces costs;
innovative design of a multi-layer foundation. The heating circuit lines are placed in a concrete base, which avoids additional measures for their installation;
the possibility of using USHP slabs to build houses on various soils. A solid foundation, in the construction of which reinforcement is used, allows the construction of objects on problematic soils;
uniform increase in the temperature of the concrete base when heated. Ensures compliance with the technology for laying heating lines;
maintaining a comfortable temperature. Thanks to the increased efficiency of the heating system and convective heat exchange processes, it is easy to maintain the required microclimate;
decrease in air humidity. Regardless of the moisture concentration in the soil, the formation of dampness, mold and mildew indoors is excluded.

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

The Swedish hot plate does not crack under the influence of forces from the weight of the building and reliably insulates the room. Along with the advantages, the USHP plate has the following disadvantages:

the complexity of carrying out repair activities associated with the difficulty of access to concreted communications;
insufficiently high durability of the Swedish stove, due to the limited service life of the heat insulator;
impossibility of arranging a basement;
the need for qualified performance of thermal engineering calculations, since the thickness of the Swedish plate depends on the characteristics and size of the insulation;
increased estimated cost of work associated with performing special thermal and strength calculations;
the impossibility of arranging a thermally insulated foundation slab in conditions of inclined terrain.

Despite these disadvantages, such a slab is superior to traditional types of foundations in many respects.

Swedish stove - device diagram and technology specifics

An insulated slab is a type of slab foundation made in the form of a sandwich.

The construction of the foundation and the laying of communications are carried out during one technological operation, which allows reducing construction time

The multilayer design includes the following levels:

communication It includes electrical cables, water pipes and sewer lines;
insulating. Includes sheet expanded polystyrene in extruded form, which thermally insulates the foundation base;
enhancing. Made of reinforcing steel with a cross-section of 12-14 mm, preventing cracking of the heated floor;
heating. It consists of a system of water mains designed to circulate coolant;
carrier. It is a concrete base that protects the heating lines and serves as the basis for the construction of the building.

Creating a foundation using Swedish technology involves a sequence of work in accordance with the requirements of the technological process. The entire foundation is immersed to a small depth in the soil relative to the zero level. Thanks to this feature, the possibility of frost heaving of the soil at high humidity is eliminated.

In what sequence is the Swedish stove installed?

Compliance with the construction algorithm of the Swedish slab affects the strength properties of the base and energy-saving characteristics. The general scope of work includes:

The soil under the insulated slab does not freeze, which minimizes the risk of frost heaving problems in foundation soils

Construction of the pit.
Installation of drainage pipes.
Laying communications.
Laying insulation.
Warm floor assembly.
Concreting.

Let's consider the main features of the stages.

Marking the area

This stage of work involves transferring the foundation project to local conditions. Before marking begins, it is important to carry out geodetic surveys aimed at determining the nature of the soil and the depth of the aquifers.

During the marking process, the following are determined:

foundation contours;
ways to connect utilities.

After marking, it is important to protect the site from precipitation by installing a storm drain.

We carry out excavation work

Earthworks include the following work:

To ensure normal operation of the insulated Swedish slab (USP) and prevent frost heaving, it is necessary to provide a groundwater drainage system

Clearing the construction site of construction debris and vegetation.
Extraction of fertile soil layer to a depth of 0.4-0.5 m.
Formation of a compacted sand layer with a thickness of 30 cm.
Extraction of soil around the perimeter of the pit for drainage lines.
Filling clay at the bottom of the pits, moistening and compacting the clay layer.

After completing the excavation work, proceed to the next stage.

Setting up a drainage system

Sequencing:

Lay down geotextiles.
Pour in crushed stone.
Compact the crushed stone.
Lay drainage pipes.
Fill in a layer of crushed stone.

After laying all layers, cover the bedding with geotextile fabric.

We lay utility lines

When performing work, observe the following sequence:

All necessary communications must be laid under the slab in advance.

Install communications.
Add a layer of sand.
Compact the sand bedding.

After installation, it is important to check the correct connection of utility networks.

We select insulation and install it

When choosing a heat insulator, give preference to insulation with reduced thermal conductivity.

It is advisable to use extruded polystyrene foam, which has the following advantages:

resistance to the development of microorganisms;
environmental cleanliness;
resistance to moisture.

Lay polystyrene foam in two layers with overlapping sheets of 40-50 cm. Use special fasteners for fixation.

We lay the reinforcing mesh and install the heated floor

When performing reinforcement, pay attention to the following points:

use tying wire to connect the reinforcement;
lay the reinforcing mesh in two tiers;
ensure a distance to the heat insulator of 30-40 mm.

Install heating lines taking into account the layout. Use plastic supports for laying pipes.

Higher thermal power of underfloor heating is achieved by denser pipe laying

When laying heating lines, pay attention to the following points:

ensuring a distance of 100 mm between heating lines;
making a distance from external walls of 150-200 mm;
correct pipe laying according to the developed diagram.

After laying the lines, check the tightness of the system with compressed air.

We install the formwork

Installation of a Swedish slab requires the construction of formwork around the perimeter of the foundation. For formwork, plywood or board panels reinforced with supports are used. The inner surface of the formwork structure is lined with polystyrene sheets. They provide thermal insulation of the foundation from the end part.

We pour the concrete mass

When concreting, observe the following requirements:

pour concrete in a 10-centimeter layer;
fill at intervals of no more than an hour;
use a vibrator or slab to compact the concrete.

Moisten the surface of the concrete during the hardening process, cover the base with polyethylene to protect it from moisture evaporation.

The Swedish slab foundation ensures the stability of buildings and has increased energy-saving properties. will ensure reliable protection of the base from moisture. According to the Swedish method, monolithic can also be poured. To build a house on an insulated base, aerated concrete blocks and slabs are suitable. When building a house, to reduce heat loss, you should pay attention to the layout of the floor slabs. An important point is sealing the seams on the ceiling between the slabs.

The classic order of construction - foundation, walls, roof, internal communications - has not changed for centuries.

An original innovation in technology was made by the Swedes, who decided to combine the process of building a foundation with insulation and laying utilities.

The result was the insulated Swedish stove, a design that won thousands of supporters. What is such a foundation, you ask?

If we use construction terminology, then this is a monolithic shallow foundation.

Briefly, its design can be described as follows: a trough-shaped bed made of durable foam, lying on a powerful sand cushion that acts as drainage.

The foam “trough” contains a reinforcement frame and concrete, in which the warm water floor pipes are laid. Sewerage and water supply are usually laid under a layer of insulation in a sand bedding.

Sometimes power supply networks are also embedded in the Swedish foundation. The surface of the insulated slab has unequal thickness. In the area of load-bearing walls it is larger (20 cm). This is necessary to increase rigidity. In other places, the layer of reinforced concrete does not exceed 10 cm. The exact dimensions of the slab in each specific case are determined by a special calculation performed by the design organization.

The load from a building standing on a monolithic slab is evenly distributed over the ground and never reaches critical values. This allows the use of the Swedish stove for houses built on weak and heaving soils.

The concrete in the Swedish slab is surrounded on all sides by chemically inert polystyrene foam, protecting it from aggressive groundwater. Powerful insulation of the load-bearing base protects the house from the forces of frost heaving, since there are no negative temperatures in the soil under the slab.

In addition to the described advantages, the Swedish slab foundation has a number of other important advantages:

The construction of such a structure and the laying of communications are carried out within a single technological operation. This significantly reduces construction time;
The thickness of the thermal insulation is 20 cm. This is more than enough to retain heat and increase the efficiency of the heated floor;
The surface of the slab is processed by grinding, so it does not require preparation for installation of the finishing floor covering;
When laying such a foundation, heavy earth-moving equipment is not needed;
A monolithic concrete slab is an excellent heat accumulator. It eliminates one of the most serious disadvantages of frame houses - the low heat capacity of the walls.

The Swedish foundation also has disadvantages:

Suitable for flat areas only. On a slope, the construction of such a foundation will be much more expensive.
High requirements for the qualification level of builders. A complex network of communications is laid in the slab and complex reinforcement is performed. Therefore, it is very difficult to make it reliably and efficiently with your own hands.
High material consumption and cost of extruded polystyrene foam - the main insulation.
Not all developers like the low base of a slab foundation.
Restrictions on the type of buildings to be erected. The USHP foundation is intended for light frame, wooden and one-story houses made of light concrete blocks.
The difficulty of repairing communications filled with reinforced concrete. There are special solutions to improve the maintainability of sewerage and water supply, but their implementation requires additional costs.

Due to simple technical illiteracy, some contractors and private developers make such a “Swedish foundation”.

It has nothing in common with classical technology, since here the insulated concrete slab does not lie on the ground, but rests on a columnar foundation. Therefore, this structure can be called a columnar foundation with a slab grillage, but not a USF.

Construction sequence

The generally accepted UWB construction technology consists of the following stages:

The top plant layer of soil is removed in an area slightly larger than the size of the future slab.
Sewer and water pipes are being laid.
Geotextiles are laid on the ground surface.
Drainage is laid along the perimeter of the slab and covered with crushed stone.
It is poured out, moistened with water and coarse sand is compacted layer by layer (thickness 15-20 cm).
A second layer of geotextile is laid and filled with crushed stone (15 cm) with compaction.
The formwork and side insulation boards are installed.
Extruded polystyrene foam is laid out on the surface of the fill in 2 layers (total thickness 20 cm).
Lay out the pipes of the warm water floor and connect them to the distribution manifold.
Reinforcement with a diameter of 12-14 mm is placed on the supports. The frequency of installation of rods is 4-6 pcs./m2.
The slab is concreted. After 7 days of curing the concrete, its surface is ground.

There are a number of technical nuances related to the technology of laying underfloor heating pipes in a Swedish stove:

Before concreting the slab, it is recommended to pump the heated floor pipes with air using a compressor to prevent collapse under the weight of the concrete.
The required power of a warm floor is determined by calculation and is achieved by changing the frequency of pipe laying.
Pipes are laid more densely along external walls than indoors.
It is not recommended to lay underfloor heating pipes more often than 10 cm apart. This leads to their overuse and the appearance of a “thermal bridge” effect (the temperature of the supply coolant is compared with the “return” temperature).
The distance between the pipes should not exceed 25 cm. Otherwise, it will not be possible to achieve a uniform temperature distribution over the floor surface.
The distance between pipes and the external walls of buildings must be at least 15 cm.
The maximum length of the heating circuit should not exceed 100 meters to avoid high hydraulic resistance.

In low-rise construction, the USHP foundation provides a combination of a minimum budget with a high resource and quality of living. This technology cannot be considered as a conventional insulated base slab - the Swedish system allows you to get floors on the ground with heating built into them. This foundation can be poured without special equipment, has minimal labor intensity, and is cheaper, second only in price.

Since the technology came from Europe, there are no domestic SNiPs for it. However, leading manufacturers of thermal insulation materials have developed albums of technical solutions for the foundation of USP, which take into account GOST standards:

7076 – products, materials for construction;
25898 – vapor permeability of building materials;
17177 – building thermal insulation;
30244 – flammability of building materials;
15588 – polystyrene foam.

When designing the Swedish “pie” of the house’s foundation, designers also take into account the joint venture:

loads, impacts – ;
foundations, foundations – , ;
basic provisions for reinforced concrete structures - ;
enclosing, load-bearing structures –;

Heat calculations are similar to MZLF systems for unheated buildings. Some polystyrene foam manufacturers make mistakes in their technical solutions for the Swedish stove.

The design of the USP is as follows:

ribbed slab 10 cm thick - a classic “floor on the ground”, the thickness of which was chosen taking into account minimizing heat loss, ensuring a normal strength reserve, ribs along the perimeter ensure the stability of the foundation in the event of possible ground movements;
underfloor heating circuits - additional heating of rooms, saving energy for the main heating circuits;
reinforced belt - two meshes of connected reinforcement bars that prevent cracking when exposed to bending loads;
engineering systems - buried below the freezing mark, duplicated to ensure maximum service life;
waterproofing - protects concrete from moisture and must have vapor barrier properties;
insulation – retains heat inside the building, accumulates heat from the subsoil, preventing freezing of the soil under the sole of the cottage;
sand cushion - has drainage properties (water cannot rise above that layer), completely eliminates the occurrence of heaving forces;
geotextiles - necessary exclusively on silty soil, it prevents mixing of the drainage layer of non-metallic material with soil particles.

Thus, the slab by default contains insulation, stiffeners and heating. The perimeter covered by this structure is reliably protected from freezing, the strength is sufficient for heavy walls (brick or block masonry on 2 floors) and roofing materials (slate, ceramic, cement-sand tiles).

In addition to the lower thermal insulation, the insulation is mounted vertically along the perimeter, duplicating the formwork of the slab base, horizontally under the blind area of the building at the depth of the base of the reinforced concrete structure. Communication pipes are laid in a shell and duplicated for all engineering systems, ensuring maintainability during operation.

Collects groundwater, flood, and storm drains, and diverts them into an underground container for recycling or pumping out using sewer trucks. Unlike mineral insulation, extruded polystyrene foam retains its properties even when immersed in water, therefore it is used in Swedish slabs without replacement options.

Advantages of USP technology

The USHP foundation requires a lot of insulation, but it is cheaper than concrete and excavation work that will be required to dig the MZLF belt. The technology has advantages:

minimum consumption of material for formwork;
guaranteed pouring of the monolith in one day;
simplification of reinforcement schemes, reduction of labor intensity;
warm + subfloor by default;
failed communications;
finished insulated blind area + drainage;
construction of a cottage on any soil without restrictions on wall, roofing materials and construction technologies;
energy saving during operation;
absence of expansion joints (only with the same number of storeys).

The Swedish slab is produced in a maximum of two weeks, which is much faster than MZLF, but a little longer than a prefabricated grillage on piles, which is only suitable for log houses, “frameworks”, half-timbering, panel and panel buildings.

Scope of application of the Swedish stove

The USP foundation is used exclusively in projects without a basement or ground floor. The technology is recommended for buildings with a side size within 15 m in the following cases:

cold regions;
high groundwater level;
the project uses bottom heating (warm floor);
when using half-timbered, frame, panel and panel house technologies;
when choosing brick or block masonry;
heaving, weak soils.

An insulated slab is not suitable for areas with complex terrain, since the soil leveled when leveling the building site does not have sufficient load-bearing capacity. In this case, the slab base will have to be reinforced with screw or bored piles to obtain a warm monolithic grillage.

USHP manufacturing technology step by step

Sufficiently adequate technological solutions for the foundation of USP are available from the manufacturer of extruded polystyrene foam TechnoNIKOL. They take into account the characteristics of the heat insulator, indicate the optimal thickness of each layer of the structure, and indicate the approximate consumption of concrete, reinforcement, and corrugated pipes for drainage sewerage. The slab has a safety margin; there is no need for expansion joints. The disadvantages are the mandatory vibration compaction of concrete to ensure the strength characteristics of the foundation of the house.

Research

To ensure that the warm slab does not collapse during operation, it is necessary to calculate the drainage system and the bearing capacity of the soil. To do this, it will be necessary to clarify the groundwater level, soil composition, and the possibility of shifting the lower layers. It is better to entrust these operations to specialists so that the Swedish “pie” for supporting the house is guaranteed to be strong.

Preparation

The foundation of the USP is prohibited from resting on a fertile layer of soil, so it will have to be completely removed. At the initial stage it is necessary:

break the axes of the main walls with cords;
mark and dig a pit (1 m more around the perimeter than the plane of the external walls);
cover the surface of the pit with geotextiles or dornite (only on muddy soil) and apply it to the side walls.

Only in this case will the Swedish “pie” not shrink. Typically, the thickness of the fertile layer is 0.3 - 0.5 m (two - three shovels, respectively).

Removing the fertile soil layer

Drainage

So that the USHP slab is always dry. It is necessary to drain storm, groundwater, and melt water from the sole. Therefore, along the perimeter of the pit, trenches are additionally torn to the depth of perforated corrugated pipes used in drainage systems. A general slope towards the underground reservoir (3 - 4 degrees) will ensure gravity flow; vertical wells in the corners of the building will provide access to the drainage system for periodic cleaning.

The drainage technology is as follows:

filling with a natural filter - crushed stone is laid on a layer of geotextile;
installation of wells - created from solid pipes (corrugated or smooth, diameter 30 - 20 cm), installed vertically;
laying corrugated pipes - they connect wells and are interrupted inside them to provide access to each line;
backfilling - trenches are filled with crushed stone and covered with geotextiles placed on the side walls.

An underground reservoir cannot be used to collect runoff from a surface storm drain to avoid overflow.

Laying geotextiles and drainage pipes

Communications layout

Installation of communications below the calculated freezing depth

A monolithic insulated slab has zero repairability. Therefore, engineering systems are laid under it before pouring. The creation of redundant systems will improve the quality of operation - if the pipeline becomes clogged, it is enough to switch to the backup circuit.

Drainage and water supply pipes are buried below the freezing mark, discharged inside the building by risers, and outside the house for subsequent connection to central, autonomous life support systems.

When laying out engineering systems, standard technology is used - sand or PGS cushion with compaction, backfilling with non-metallic material.

At the same stage, the pit is filled with sand (compacting every 20 cm with a vibrator or manual tamper) to the design mark.

The sand layer must be compacted layer by layer with a special vibrating plate.

Thermal insulation

To ensure spatial rigidity and high-quality positioning of the warm slab on the ground, the structure has ribs on the lower surface. The following scheme is used for this:

the first layer of XPS expanded polystyrene covers the entire perimeter of the building;
the second layer of XPS insulation is shifted 45 cm from the edge to create ribs around the perimeter; in the middle part of the slab, grooves 20–30 cm wide are created in the heat insulator;

XPS sheets manufactured by URSA, Stirex, Technonikol, Penoplex, Technoplex with a thickness of 10 cm are used. Suspension PSB-S, produced without pressing, is not suitable for this technology.

Laying the first layer of insulation

Base insulation device. Be sure to leave protrusions for further joining with the insulation of the blind area.

Laying the second layer of insulation

Reinforcement and installation of heated floors

A monolithic Swedish stove is multifunctional only if water heating circuits are integrated into it. They can be placed on top of the top reinforced belt or between grids of reinforcing bars. This takes into account the design of rooms, the passage of partitions and even the arrangement of furniture.

The collectors are brought to the design level, the system is pressed before the formwork is filled with concrete mixture. Polymer pipes are mounted on special plastic stands, similar to reinforcing bars.

Laying the first layer of reinforcement and installing heated floor pipes

Depending on the operational, snow, and structural loads, armored belt houses are assembled from bars of periodic cross-section with a diameter of 12 - 16 mm. One layer (bottom), given in the recommendations of some authors of USP methods, is ineffective in difficult operating conditions.

Therefore, experts recommend using the classic scheme of two meshes created from connected reinforcement. The stiffeners use frames of the same type, connected to the main lattice of the slab. The recommended characteristics of the armored belt are as follows:

grid pitch – 15 x 15 cm in both zones;
the frequency of distribution clamps in stiffeners (vertical, horizontal jumpers) is 25-30 cm;
6 – 8 mm reinforcement for jumpers and clamps.

Laying the second layer of reinforcement

Connecting underfloor heating pipes to collectors

Formwork

Formwork for insulated Swedish slab.

When installing formwork, two options are possible: classic panels with sheets of expanded polystyrene leaning against the internal surfaces or L-panels made of the same material. There are disadvantages in both cases - additional costs for plywood/boards, L-panels, respectively.

The height of the formwork must correspond to the project, taking into account the thickness of the heat insulator (20 - 30 cm for different regions), the slab (10 cm). When using classic plywood formwork, boards can subsequently be used in the next stages of house construction, since contact of lumber with concrete is completely excluded.

Fill

Pouring a Swedish slab with concrete.

A foundation of this type must be poured in one go; interruptions with the delivery of concrete mixes by mixers for more than an hour are not recommended. Due to the variety of communications inside the formwork, the presence of different levels, and stiffeners, vibration compaction is a prerequisite.

In this case, surface and deep vibrators can be used, the tips of which are lowered into the concrete layer every 20 - 30 cm. Contact with reinforcement and heated floor pipes is highly undesirable.

Stripping is possible after the concrete mixture has gained strength (3 days), surface care is standard - periodic moistening with a watering can, covering with PVC film in hot weather. Experts recommend building USHP at the end of summer, when groundwater levels drop and the weather is more stable.

A prerequisite is to grind the slab with special equipment. Otherwise, you will have to increase the construction budget for the production of the leveling screed. Even with vibrocompression it is impossible to achieve a perfectly flat surface of ready-mixed concrete.

Even before the advent of high-strength insulation materials, solid slab foundations were considered an effective means of compensating for seasonal (frost heaving) and non-seasonal soil movements. Being “floating”, they maintained the relative position of all elements of building structures relative to each other, even when houses fell into areas of small landslides. An original engineering innovation that combined the solution to energy efficiency problems was the so-called USP foundation, the technology of which came to us from Sweden and Germany. This article describes the design and operational features of the insulated Swedish stove (as the abbreviation “USHP” stands for).

About 10 years ago, the first domestic enthusiasts, developers, used standard projects from this particular company. According to Dorocell, the optimal energy-efficient foundation for low-rise housing construction is a high-quality monolithic concrete slab with stiffeners, external thermal insulation and built-in heating.

Scheme of the technology for installing an insulated Swedish USHP plate using TechnoNIKOL materials

Thermal insulation, representing a kind of “trough” for pouring concrete, serves as a natural permanent formwork.

Here is a detailed overview of the foundation of an insulated Swedish slab:

Formwork made of polystyrene PSB-S is assembled on a compacted sand and crushed stone bedding. At the bottom of the backfill bed, slopes were made and a drainage pipe was installed.
Formwork 400 mm high consists of slabs 100 mm thick and forms rectangular grooves with a cross-section of 400×200 along the perimeter to form stiffeners and a bed for pouring the main slab 100 mm thick.
Reinforcement of the ribs is carried out in two belts with a profile of variable section with a diameter of 8 - 12 mm. Reinforcement of the floor slab is carried out using a welded mesh 150x150 mm.
The heating system pipelines are embedded in the floor slab. The floor slab is reinforced using a 150×150 mm welded mesh laid on top of the heated floor pipes.
In addition to the heated floor, other communications are also poured with concrete - water supply, sewerage, electrical wiring in the rooms.
Insulation of the blind area is carried out along the perimeter of the foundation with 70 mm PSB-S slabs adjacent to the polystyrene formwork from the outside at the depth of its contact with the bedding.

Thermal insulation skirt around the foundation slab protects against freezing

The described scheme corresponds to the load generated by a two-story house with load-bearing walls made of cellular concrete, as well as climatic conditions with a frost index of 4000 - 8000. An increase in load requires an increase in the cross-section of the stiffeners, and a more severe temperature regime requires the addition of one or two additional layers of insulation.

There is an alternative technology for installing an insulated foundation: UFF - insulated Finnish slab. An overview and features of this type of foundation are described in

The best video about USP technology

Pros and cons of the Swedish stove

The most important thing is that as a result of installing the foundation according to the warm Swedish stove scheme, the developer receives a solution to a whole range of issues:

effective drainage,
anti-frost protection,
energy saving,
heating,
comfortable microclimate,
laying communications,
as well as obtaining a floor surface for finishing coatings.

Other benefits of the scheme include:

For frame houses, USHP compensates for their main drawback - the low heat capacity of the walls. A massive insulated foundation takes on the function of a backup heat accumulator.
Price. Despite the fact that the Swedish scheme is not a cheap pleasure, it includes not only the zero cycle, but a whole set of stages. Performing these works separately costs significantly more in total.
Deadlines. When the work is carried out by a team of qualified specialists, everything will take, on average, about a week.
Versatility. The technology is suitable for most soils and climatic zones of the Russian Federation.
Indispensable in the construction of “passive house” class buildings.

Disadvantages of a foundation based on a warm Swedish stove:

Conditional (psychological) disadvantage: low base. In houses with a regular foundation, a high base is necessary to ensure normal humidity in the rooms. Until now, many of our compatriots tend to consider the height of the basement as one of the guarantees of housing quality.
Maintainability of communications. Since the floor slab is a stressed structure, it is extremely undesirable to violate its integrity to repair bricked up pipelines. On the other hand, there are other installation methods and technical solutions that compensate for the shortcomings of the circuit. But all these measures lead to an increase in costs.
Requires highly qualified performers. Not every team will take on the turnkey delivery of the USP.
It requires significant one-time capital expenditures, therefore it is not suitable for developers who expect construction in small (in terms of money) stages.
Not suitable for peaty soils and other soils with low bearing capacity, as well as areas with large slopes.

Technology development: methods, materials, components

To date, more than 1.5 million houses have been built under the USP scheme in Germany and the Scandinavian countries. In Northern Europe technology insulated monolithic slab foundation received generally accepted status and is reflected in EU building standards. In the USA, complete external insulation of slab foundations is not widespread, since 90% of the country has a frost index of no more than 3000. However, USP has also found application there: first of all, in the construction of “passive houses”.

Over the past 10 years, project developers have given greater preference to extruded polystyrene foam (EPS) as a material that provides more uniform shrinkage of foundations and maintains thermal insulation properties regardless of time and operating conditions. The stresses in concrete arising during the operation of shallow slab foundations were studied in detail. Based on their results, builders abandoned the idea of using insulation materials with different ultimate strengths (previously it was assumed that in order to equalize shrinkage under the floor slab, it was necessary to use less strong slabs than under the stiffeners). It has been proven that the most dangerous stress concentrators in a slab can occur at the junction of different types of heat insulation.

Manufacturers of extruded polystyrene foam began to produce materials and components specialized for the installation of USP.

For example, Dorocell itself currently produces a complete set of “designer” parts for permanent formwork made of EPS. The company's calling card is blocks with built-in guides for fittings. Some brands pay increased attention to the aesthetic properties of the components: the sides of the formwork are molded in the form of plinths of a traditional variable section.

If we talk about the domestic market, then there are 2 brands on the market: TechnoNIKOL and Penoplex. Both companies produce EPS of European quality level for slab foundations built using USHP technology. I would like to dwell in more detail on the specialized series TECHNONICOL CARBON ECO SP. In addition to the basic slab formats, it includes L-shaped profiles for quick installation of sides. In addition to the cross-section, these elements are interesting because CSP (cement-bonded particle boards) are fixed to their base parts on the outside. DSPs allow you to apply decorative plaster without additional preparatory stages. Thus, installation of USP using TechnoNIKOL components is currently the most convenient.

Algorithm for installing an insulated slab foundation

For a full cycle of work on arranging the USP, you will need the following basic materials:

Geotextiles;
100 mm EPS slabs for formwork and 70 mm slabs for insulating the blind area;
fittings Ø12; welded mesh 150×150;
Concrete grade not lower than M350 with the necessary additives, taking into account the pouring time and air temperature, anti-capillary crushed stone, coarse sand;
Pipes of the PEX or P-PE type for a pressure of at least 6 bar at a coolant temperature of up to +95°C, as well as a protective corrugation;
1"" collectors (for a house with an area of no more than 250 sq. m., in most cases, 2 pieces are needed);
Shut-off valves consisting of Eurocone compression fittings, 1" ball valves and a system crimping unit;
Special fasteners consisting of disc-shaped dowels, studded plates, FS-30/40 clamps, double-sided tape.

After completing geological surveys, strength calculations and purchasing materials, the future foundation is marked. Based on the addition of 0.3 - 0.5 m to the edge of the insulated blind area, the perimeter is determined. The axes of the internal load-bearing walls are marked, as well as the points and directions for laying communications. Further work is carried out as follows:

Removing fertile soil;
Laying geotextiles along the bottom with overlapping joints of at least 15 cm;
Layer-by-layer backfilling with crushed stone and sand is carried out. Each layer of 10 - 15 cm is compacted with a vibrating plate with added water for greater compaction;
Laying communications - water supply, sewerage, power cables, ground loop, drainage system. When laying sewer lines, ensure slopes. When arranging drainage, in addition to observing slopes, provide drainage wells. Check the operation of the slopes with water.
Backfill drainage and sewer trenches and check the overall plane of the backfill pad.
Start assembling the insulating formwork. If L-shaped profiles are not used, then you will need to do a significant amount of work. First, the slabs are glued end to end at an angle of 90° using a special glue. For additional fastening, disc dowels and plastic fastening corner elements are used. Secondly, the resulting sides need to be fixed from the outside with plywood or boards, supporting them with slats.
Starting from the second or third layer of polystyrene, niches for stiffeners are formed during installation. The slabs are laid in a horizontal plane “in a staggered manner”, with the joint line offset.
If necessary, a vapor barrier layer is laid on top of the last layer of EPS.
Let's start reinforcing the stiffeners. Reinforcement is provided by four longitudinal reinforcement bars Ø 10 - 12 mm, forming the upper and lower chords. The load-bearing frames are connected using special clamps outside the formwork. The finished power units are installed in the grooves and secured using FS clamps.
Using the same clamps, a 150x150 mesh is mounted for the floor slab (rod diameter 6 - 10 mm).
Heated floor pipes are installed over the laid mesh and secured with nylon clamps. When crossing stiffeners and doorways, pipes must be protected with corrugations.
After installing all the heated floor circuits, they are connected to the collector. The places where pipes rise to the collector are protected by corrugation.
Each circuit is filled with coolant separately. Filling is carried out through the manifold until all air is displaced from the system. Then leak tests are carried out. After testing, it is necessary to crimp all connectors of the system.
Before concreting, it is necessary to check the structure. The check consists of control measurements of the formwork, inspection of the reinforcement, clearing the site of debris, protecting communication terminals from concrete, as well as checking the fixation of these terminals on the formwork. At the end of the preparation, the entire initial situation with the location of communications should be captured in detailed photographs and an internal inspection report of the formwork and engineering systems should be signed.
We select a concrete supplier and order him a mixture with the properties required by the project.
On the day of concreting, large equipment (mixer, concrete pump) is placed, the mixture is accepted for quality, the mixture is laid and maintained. Laying work is carried out in accordance with the standard for carrying out this type of work in compliance with working methods and time intervals. During installation, it is necessary to carefully monitor the flow of mortar under the reinforcement elements. The surface is leveled using vibrating slats. Vibration processing of the incoming mixture is provided in the stiffeners. In order to ensure the required dehydration regime, the concrete is covered with polyethylene film.
In the future, it is necessary to monitor the progress of dehydration and check the surface for a strength gain of 15 kgf/cm2. This indicator makes it possible to carry out other construction work at the site.
While the concrete is gaining strength, you can organize cleaning of the area and lining the outer surface of the base with finishing material.
After covering the base, it is necessary to organize a blind area. It is recommended to lay a drainage membrane on top of the blind area slabs. At the end of the work, the blind area is backfilled.

What stages of installing an insulated Swedish stove are acceptable and advisable to do yourself? If you do not have experience in carrying out the types of work described, then you can only recommend paragraphs for doing it yourself. 2; 6; 7; 8; 10; 14; 15; 17; 18; 19.

Persons who have the necessary skills, but work alone at their site, are allowed to carry out all types of work except concreting. An exception may be objects with a small area (up to 30 - 40 sq. m.).

If you are pursuing the goal of building a house with zero energy balance, then one of the most attractive types of foundations will be USP. The technology of its device has already been brought to technical perfection and tested over decades of operation; today we will describe it in detail.

Insulated slab design

Unlike a conventional monolithic slab, the USHP foundation has a number of structural features that provide it with outstanding stability and heat saving characteristics. Another characteristic feature of the Swedish stove is the use of premium quality materials. This implies significant financial investments, but the result is definitely worth it: with a service life of over 50-70 years, the developer receives a finished floor with almost solid insulation and the opportunity to establish a multi-story building even on very weak and heaving soils with high groundwater level.

The insulation of the Swedish plate is carried out with a special assortment of products made from extruded polystyrene foam. Since even with a relatively small thickness the slab can have a significant dead weight and withstand the weight of a building up to 2-3 floors, the insulation material must be highly resistant to deformation during compression - from 200 kPa. Cheaper PSB cannot boast of sufficiently high strength indicators.

Elimination of frost heaving under the foundation is achieved by a continuous insulation belt around the perimeter of the foundation and the installation of a blind area that drains water. The insulation under the blind area is usually 50-70 mm, with the thermal conductivity of the insulating materials not exceeding 0.035 W/m*K. With the same indicators, the thickness of the insulation layer of the slab itself can reach 200-250 mm. The maximum deformation value of high-quality insulation under full load at this thickness is about 10-15 mm.

Another feature of the USP is increased strength and spatial rigidity, which is achieved due to the special configuration of the lower part of the foundation. Along the perimeter and under the load-bearing walls, the slab has protruding ribs that evenly distribute the load over the entire area of the support and give it very high rigidity. Even during the construction of a two-story stone house, the pressure force on the ground rarely exceeds 0.6-0.8 kgf/cm 2, accordingly the building will stand stably even on moisture-saturated sandy loam, peat soil and plastic clay.

In view of the features described above, the main task in the construction of the USP is to ensure that the slab does not experience deformation under the weight of building structures. In general practice, the height of the stiffeners is from 2 to 5 times the thickness of the slab. Moreover, if the span between the ribs exceeds 50-70 times their thickness, the slab is reinforced either with a denser reinforcement scheme or by installing additional intermediate ribs.

Excavation and preparation

In reality, there are quite a few configurations of the Swedish plate, differing in thickness and reinforcement pattern. However, this does not change the essence of the technology for a very extraordinary reason, which is quite difficult for the average person to accept. The fact is that the durability and stability of the USP are ensured not by the design of the slab itself, but by the correct preparation of the base underneath it.

It all starts with removing the fertile layer of soil or digging a deeper pit if a basement is planned under the house. In this case, the bulk of the soil is removed in an area larger than the slab itself. In each direction from the planned foundation markings you need to retreat 40-50 cm plus the depth of the slab, multiplied by approximately 1.35-1.5. This need is due to the fact that a dense, incompressible bedding is prepared both under the slab and under the blind area, which easily “releases” the water. In this case, the width of the blind area is always determined by the depth of the foundation, because the spread of liquid when seeping through the bedding occurs like a fan. Thus, the greater the depth, the wider the wetting spot. The radius of this spot for the bedding material under the slab is approximately one and a half times greater than the depth.

After removing the soil, the pit is cleaned manually and covered with needle-punched geotextile, then it is backfilled. The first is sand - high-quality river sand, without clay inclusions and with the lowest possible compaction coefficient, that is, fractions from 1.3 to 2 mm. Sand is poured in layers of 50-70 mm and compacted by vibration with a slab weight of about 100-120 kg. The thickness of the sand bedding is at least 20 cm, but in general it can reach 2-2.5 times the nominal thickness of the slab. It usually does not make sense to arrange a thicker layer of sand.

If groundwater may appear at the resulting elevation, a system of drainage pipes wrapped in geotextile is placed in the pit around the perimeter to prevent silting. To ensure the necessary slope, small gutters are undermined in the sand, but the overall plane remains strictly horizontal. After installing the drainage system, the pit is covered with geotextile with a density of 250 kg/m2, then gravel of a fraction of 15 to 30 mm is poured. In the best case, granite crushed stone is used, which is poured in layers with a gradual reduction in the fraction down to 10-15 mm.

The functions of the gravel bed are to drain the lower plane of the slab and distribute the load. Backfilling is carried out to the mark at which it is planned to support the slab ribs. The depth of support is determined by the thickness of the slab with stiffeners, taking into account that the plane of the finished floor will be 20-25 cm above the adjacent soil.

Installation of insulated formwork

The Swedish stove has a continuous belt of insulation of the lower plane without cold bridges. Arranging such a thermal protection scheme is quite simple for a flat slab foundation, but the presence of ribs makes its own adjustments. Especially for this purpose, special products are produced for the formation of permanent formwork.

The formation of external stiffeners is carried out using L-shaped trays, which are placed around the perimeter of the slab and aligned with marking cords and a level. The outer edge of the trays determines the overall thickness of the slab and ribs; the inner edge is formed manually using slabs cut in place. The necessary strength of the formwork to withstand loads during pouring is provided by external decks made of sheet materials, supported by stakes driven into the ground along the upper and lower chords.

When the formwork of the ribs is assembled, the space between them is filled with thorough compaction by washing or vibration. Backfilling can be done with sand or fine road gravel, there is not much difference. In order not to disturb the geometry of the formwork, temporary plastic bridges are inserted into the trays.

When filling cavities between the ribs, it is not brought flush with the internal walls. Instead, the internal walls protrude to the thickness of the insulation boards used. After the outer thermal insulation belt is assembled, the formwork is covered with a profiled type waterproofing membrane. In the corners, the hydrobarrier is carefully trimmed and placed on top of each other with an overlap of 150-200 mm, snapping the pimpled locks.

An internal insulation belt, represented by 2-3 layers of 50-70 mm EPS, is mounted on top of the waterproofing. In this case, the size of the trays is reduced by the thickness of the insulation, which must be foreseen in advance. Fixation of EPS is usually not carried out, since the formwork is constructed the day before pouring or a day earlier. In case of strong wind, the slabs can be tied together using small portions of universal glue or pressed down with pressure before assembling the reinforcement frame.

USHP reinforcement

The insulated Swedish slab contains a small amount of reinforcement, but it is correctly distributed in the thickness of the concrete for maximum load absorption. The assembly of the reinforcement frame begins with the ribs: U-shaped clamps made of smooth structural reinforcement with a diameter of about 8 mm are placed in them, the size of which is selected taking into account the protective layers of concrete of 50 mm on each side. The tails of the clamps extend 20-25 cm above the top reinforcement line of the common plane.

The slab itself is reinforced with two layers of mesh made of rods from 8 to 14 mm in two rows, and the thickness of the rods in each layer is different. Due to the fact that the main load on the plane of the slab comes from the resistance of the soil, the main working reinforcement, which absorbs tensile loads, is located in the upper zone and the thickness of the rods is higher here. The bottom row is made of thinner reinforcement, but with a smaller cell size; it is necessary to impart monolithic strength; it is also used as a mounting system for fastening communications.

When laying the mesh, it is knitted in place, placing the longitudinal rods on remote chairs, providing a protective layer from below of about 40 mm. Transverse rods are laid on top, all intersections are tied with wire. To securely fix the top row, U-shaped anchors are tied to the bottom mesh, to the upper tails of which the longitudinal rods of the main reinforcement are attached with wire. After the upper mesh is completely connected, the reinforcement frames of the ribs are raised slightly, the tail outlets are bent and tied to the rods of the upper row of reinforcement.

Laying communications

The construction of the USP is carried out in such a way that all the necessary communications or channels for their installation remain in the slab. In order not to lose sight of anything, here is the maximum list of what can be hidden in the thickness of concrete:

Tubes or heating cable for underfloor heating;
Supplying water to the house;
Sewage channels with outlets in bathrooms and riser locations;
Water supply outlets for household needs;
Input electrical cable in a protective sheath or just a sheath with a cord for pulling;
Electrical outlets for street lighting and household needs;
2-3 spare channels for pulling communication lines or additional cables.

It must be taken into account that the hidden installation of communications when placing metering units inside the building may require the execution of a hidden work certificate. To prevent communications from being damaged during pouring, they are laid exclusively inside rigid shells, the most budget-friendly example of which is technical HDPE pipes made from recycled materials. To prevent the pipes from being crushed by the mass of concrete, they are jammed and spool valves are inserted to pump air under a pressure of 3-3.5 atm.

Concrete pouring and processing

The advantage of the Swedish slab is that concrete work takes place in one stage, and therefore the construction speed is one of the highest. A real Swedish slab requires factory-prepared concrete. This requirement is related not so much to the need to ensure the exact value of the grade, but to the need to fill the entire slab at one time without the formation of cold seams.

Since the Swedish slab is installed on a drained site, concrete with a strength class of B20 and higher is suitable for its production, but without any special claims to frost resistance. The discharge of the concrete mixture begins from the center of the formwork so that the walls of the trays experience the dynamic impact of water hammer only at the final stage of pouring. As the form is filled, the concrete is carefully compacted with an in-depth vibrator, and due to the relatively small thickness of the slab, there is no fear of delamination.

Leveling a concrete slab can be done manually followed by grinding, or it can be immediately brought to zero using a vibrating screed. The finished floor surface in both cases is ready for laying most light coverings, from linoleum to parquet boards.