How to insulate a slab foundation with polystyrene foam? What is slab foundation insulation? What insulation is better for the foundation of a monolithic slab.

The slab base withstands significant external influences and is suitable for construction in areas with complex, unstable soils prone to frost heaving, with high level ground water. Insulation of the foundation slab will help to significantly reduce heat loss through the base and reduce the effect of frost heaving of the soil. The building, when the soil moves, rises and falls along with the foundation, which protects the structure of the house from cracking.

general information

The design of the slab base consists of layers:

• geotextiles are covered with overlapping strips on the sandy layer, the joints are glued with adhesive tape;
• pour gravel, a layer of 15-20 cm;
• pour the leveling layer cement mortar, 5-10 cm thick;
• be sure to isolate the structure from moisture with the help of roll or coating materials;
• arrange a heat-saving layer;
• obscure polyethylene film overlapping stripes by 20 cm;
• lay the reinforcing mesh;
• poured with concrete.

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

Advantages of the slab foundation

The slab base has the following advantages:

• the concrete slab acts 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 whole house with it move simultaneously with the soil;
• you can mount the plate on any type of soil, even on peat bogs and swampy areas;
• the slab is erected above the level of soil freezing; thanks to the sand cushion, frost heaving practically does not affect the structure;
• reinforced concrete slab is not subject to shrinkage;
• suitable for building up to 3 floors.

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

Advantages of slab thermal insulation

Polystyrene foam, polystyrene foam, polyurethane foam are used as heat-insulating material. Mineral wool is unsuitable due to its low strength and high moisture absorption.

There is a technology for mounting a Swedish plate. 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 and does not heave.

The main advantages of the Swedish plate 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 warm floor;
• installation of the foundation is carried out without involving a large amount of construction equipment.

Around the building, a drainage system is provided, consisting of pipes for draining rain and melt water.

The design of the plate contributes to the transfer of all loads from the building to the layer of heat-saving material, therefore, increased requirements are imposed on the materials used.

Disadvantages of slab foundation

A slab foundation is not always the best option. Always do everything in advance necessary calculations and choose the most suitable type of foundation for the house.

Disadvantages of the plate:

• not suitable for erection in areas with a slope;
• to build a house with a basement on a slab, you need to deepen it to a great depth, it will be very expensive;
• it is difficult to repair communications under the foundation slab;
• during construction in winter, additional costs will be required for heating concrete and maintaining desired temperature Location on.

A slab foundation is erected only when a strip foundation is not possible.

Materials for insulation

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

№	Thermal insulation material	Characteristics
1	Styrofoam	Consists of cells filled with air. It is produced in the form of sheets, has insufficient density, so its surface needs additional protection.
2	Extruded polystyrene foam	Able to withstand significant compressive loads without changing its size and structure. Produced in sheets rectangular shape with small cells filled with air. Stack sheets in 1 or 2 layers. The second layer must be laid out so that the seams of the sheets of the first and second rows do not intersect. During installation, provide holes for moisture removal.
3	polyurethane foam	It is a kind of foamed plastic with many pores filled with air bubbles. The composition is prepared directly at the construction site. The two components are mixed, resulting in a dense hard foam, which is applied to the surface. The plate insulated with polyurethane foam has high rates of heat and sound insulation, withstands moisture. Refers to low-combustible materials, and some brands are slow-burning.

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

Installation of an insulated plate

The construction of a monolithic slab base requires the performance of all calculations, taking into account geological, climatic conditions and the mass of housing construction.

Insulation of the slab foundation allows you to save significant funds on heating the premises during operation.

Site preparation

At the stage of creation, the project must take into account that the area for the foundation slab must be wider than the housing construction by at least 1 m on each side.

Instructions for performing preparatory work:

1. The site where construction is being carried out is cleared of debris, the root system of trees and shrubs.
2. Mark the position of the plate according to the project.
3. They clean and remove the fertile layer of soil. The degree of deepening of the plate depends on the geological and climatic conditions. Most often, the thickness of the plate varies from 20 to 30 cm, less often the base is buried by 50 cm.
4. They dig a pit, manually level its bottom and side walls.
5. Pipes are installed around the perimeter to drain rain and melt water.
6. Lay the geotextile in overlapping strips. The material should cover the bottom and go to the walls along the entire height.
7. Drive in wooden stakes or metal rods. Stretch the cord strictly horizontally. It will serve as a guide for uniform backfilling of sand and gravel.
8. Sand is poured, 20-30 cm thick. Sand is evenly distributed over the entire area, moistened with water and compacted well.
9. Spread geotextiles.
10. Crushed stone is poured, evenly distributed around the perimeter, carefully rammed.
11. Conduct all necessary communications. They dig trenches under them in rubble a little wider than the section of pipes. The pipeline is laid, 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.

Plate insulation

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

1. They mount a removable formwork from boards, install props so that the structure does not fall apart under the weight of concrete.
2. A layer of concrete is poured, 50 mm thick.
3. After the cement mortar has completely hardened, foam sheets are laid on it butt against each other and glued. The adhesive composition is applied with 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, with an offset of 1/3. When laying in two rows, the joints must not intersect.
4. Spread dense polyethylene with overlapping stripes. The joints are sealed with adhesive tape.
5. The reinforcing cage is laid, the formwork is poured with concrete.

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

The insulated plinth helps to increase heat saving inside the room.

When installing insulation on bituminous insulation, you need to wait for it to dry completely. If laying on a wet layer, the materials may be damaged and the effect of thermal insulation and waterproofing will decrease.

Rules for installing heating pipes

When installing the UWB, heating pipes are used. There are such rules for their installation:

• A denser laying of pipes allows you to get higher temperatures for heating the room.
• The distance between the outer walls and pipes should not exceed 150 mm. Closer to the center, the laying step can be increased up 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 apart.

It is impossible to mount heating pipes at the junctions of monolithic plates. 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 a warmed Swedish stove with your own hands can be seen in the video:

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

The slab type of foundation has a different name - floating, since the slab can be erected on bulk, eroded, weak soils and with a high rise in groundwater. acts as a raft on which the house "floats".

This type of foundation is ideal for small buildings. Its functions are similar to the functions of other types of foundations: thanks to the slabs (their rigidity) located under the entire area of ​​the building under construction, it is a deterrent to the movement of soil and protects the house from destruction.

The slab foundation refers to one of the types of shallow strip foundation. Its main difference is that it uses a solid slab made of reinforced concrete and rigidly reinforced over the entire bearing surface of the slab.

Unburied foundation slab:

• makes it possible to reduce concrete consumption by 30%;
• labor costs for installation up to 40%;
• the cost of the foundation as a whole up to 50%;
• applicable to almost all types of soil;
• short construction time.

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The technology of building a foundation from slabs

The construction of a slab foundation begins with the fact that only a fertile layer of soil is removed on a previously prepared and marked area. A sand cushion with the addition of sand is laid at the bottom of the dug pit, which is well compacted. A layer of waterproofing material is placed on the pillow, then a layer of insulation. After that, the foundation of the slabs is carefully reinforced. For slabs, reinforcement d \u003d 12 mm is applicable. And the last stage is the construction of the formwork and pouring concrete into it.

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Foundation slab: insulation

It will help to reduce heat loss through the slab, and, accordingly, eliminate subsidence of the soil under the slab. To do this, lay a 10- or 15-centimeter layer of heat-insulating material. From freezing to save the slab foundation will help its insulation between the slab and the ground.

The issue should be given special attention to residents of regions with severe climatic conditions and deep freezing soil.

The zone makes up about 80% of the entire territory of Russia. Heaving soils during freezing increase in volume and rise, which causes the destruction of the foundation structure.

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Advantages of thermal insulation of the foundation slab

• relieves (or significantly reduces) the influence of frost heaving forces on the foundation;
• reduces heat loss through the foundation and reduces heating costs;
• creates the necessary conditions to establish a constant required temperature indoors;
• prevents condensation on surfaces inside the building;
• serves as protection for waterproofing against mechanical damage;
• prolongs the life of the waterproofing material.

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How can you insulate a slab foundation?

Thermal insulation materials for absorbing moisture should not, as well as shrink under soil pressure. High performance water absorption and compressibility when backfilled with soil make mineral wool not really suitable material as a heater. Only foam glass and expanded polystyrene meet these requirements. The first option will cost several times more.

Can regular styrofoam be used? Can. Only it must be placed on a waterproof layer (waterproofing), which serves as protection for structural elements from ground moisture. Otherwise, after a few years from the moment of installation, the foam can be expected to turn into a shapeless pile of balls. The accumulated moisture in the insulation during freezing will increase the foam in volume, while destroying its structure.

Extruded polystyrene foam is considered the most optimal heat-insulating material for conditions of increased loads and humidity.

Due to the characteristics of the raw materials and the closed cell structure that prevents the penetration of water into it, the expanded polystyrene boards have excellent technical specifications, long service life, which makes it possible to use it in the insulation of foundation slabs.

Extruded polystyrene foam has a water absorption close to zero (no more than 0.5% by volume for 672 hours and for the entire next period of operation). This does not allow ground moisture to accumulate in the thickness of the insulation, expand in volume under the influence of temperature changes and destroy the structure of the material during the entire period of service.

In order to insulate the slab foundation for the purpose of vertical thermal insulation of civil and industrial facilities polystyrene is used with a compressive strength of at least 250 kPa (linear deformation - 10%). For private low-rise construction, slabs with a strength of at least 200 kPa can be used, since in this case the depth of the foundation will be less, and at the same time, the pressure of groundwater and groundwater on the insulation is lower. For structures that require increased strength indicators (loaded floors), it is necessary to select plates with a compressive strength of 500 kPa.

The advantages of expanded polystyrene:

• stability of thermal insulation properties throughout the entire service life;
• validity period - 40 years;
• compressive strength index - 20-50 t / m²;
• is not a breeding ground for rodents.

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How to insulate a slab foundation with polystyrene foam?

While insulating the vertical part of the foundation, expanded polystyrene is set to the depth of soil freezing, which is determined individually for each region. If you install a heater deeper, the efficiency of this will drop sharply.

The thickness of the thermal insulation layer in the corners should be increased by one and a half times with an indent on both sides of at least 1.5 m.

Insulating the outside is a more rational way, since this way the level of heat loss will be lower.

Heat-insulating plates are laid on a layer of waterproofing. If you plan to use knitted reinforcement for reinforcing monolithic iron concrete slab foundation or load-bearing floor, then for expanded polystyrene plates it is necessary to arrange protection from the liquid components of concrete. To do this, use a polyethylene film (150-200 microns), which is laid in one layer. If reinforcing work involves the use of welding, then a screed of low-grade concrete or cement mortar must be made over the film to protect it. Polyethylene is laid with an overlap of 100-150 mm on double-sided tape.

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External insulation of the foundation

Reduce the depth of freezing of the walls and, keep the freezing boundary in the thickness of non-rocky soil - sand and gravel cushion and backfill soil insulation around the entire perimeter of the house under the blind area construction will help.

When laying polystyrene foam, it is important to take into account the given slope of the blind area - about 2% of the house. Not less than the depth of seasonal soil freezing should be the width of the thermal insulation of extruded polystyrene foam around the perimeter.

The horizontal thickness of the thermal insulation must not be less than the vertical thickness of the foundation thermal insulation.

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Internal insulation of the foundation

If it is not possible from the outside, thermal insulation is allowed from the inside of the foundation walls.

Laying thermal insulation from the side of the walls of the room is carried out either by gluing extruded polystyrene foam to the surface of the walls with solvent-free compositions (can be cement-based), or by mechanically fixing the insulation boards with subsequent finishing.

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How to fasten sheets of expanded polystyrene to the foundation?

The insulation is placed on the leveled surface of the walls outside the insulated structure with waterproofing already made on it.

It is not allowed to mechanically fix the expanded polystyrene plates from the outside when insulating the foundation plates. Since in this case it is possible to violate the integrity of the continuous waterproofing coating.

To a surface on which there is already a waterproofing layer, expanded polystyrene plates can be attached in two ways:

• glue;
• method of melting bitumen on waterproofing.

The adhesive agent is applied at 5-6 points, then the plates are pressed tightly to the surface.

The gluing of the slabs must be carried out from below, laying the slabs in a horizontal row. The second and subsequent rows of plates are fastened end-to-end to the previous already glued row. Re-installation of glued boards is not allowed, as well as changing the position of the boards after a few minutes after gluing.

Thermal insulation boards must be of the same thickness and touch each other and the base tightly. At the same time, it is necessary to arrange them by shifting the joints (in a checkerboard pattern). If the distance of the joints between the plates is more than 5 mm, they must be filled mounting foam. The plate is best used with a stepped edge. The slab is laid close to the adjacent one so that their adjacent parts of the edges overlap each other. With this installation, no cold bridges appear. When arranging a two-layer (or from a larger number of layers) thermal insulation, the seams between the plates are placed in a run.

Users of our portal have accumulated vast experience in building foundations. Starting from tape, pile, monolithic slabs and ending with the popular type -, and willingly share their knowledge with novice developers. was no exception and Turkish945. The user spoke in detail about all stages of the construction of an insulated slab foundation for a garage-workshop-boiler room, 7500x7500 mm in size.

Turkish945 Member FORUMHOUSE

I spent a long time analyzing which foundation to choose. As a result, I settled on the type of UWB. At first I thought about making a plate with stiffeners, then without ribs. But one thing bothered me - whether a 10 cm thick plate would withstand a point load from a TA (heat accumulator). Therefore, I decided not to engage in amateur performances, but to order a foundation project.

After the calculation, it turned out that the thickness of the slab should be increased to 20 cm, otherwise there is no guarantee that it will withstand the expected load. Judging that the savings of 30 thousand rubles. (the difference between the thickness of the slab is 100 and 200 mm) this is an unjustified risk, the user settled on the second version of the foundation.

The foundation is a layer between the building and the base, which redistributes the load from the house to the ground. The foundation must be built not by eye and not according to the principle “so the neighbor did”, but designed on the basis of data from a geological study of the soil (this will allow you to find out bearing capacity) and with further collection of all loads from the building.

Having decided on the foundation project, the user hired an excavator to dig the foundation pit. In total, about 50 cubic meters of soil were selected and taken out. In addition, we managed to negotiate with the excavator and at the same time uproot the bushes and trees on the site. For this work, they gave 15 thousand rubles (at prices in the Moscow Region for 2015).

The height error at the bottom of the pit did not exceed 50 mm. Also Turkish945 asked the users of the portal what to do with the grooves at the bottom of the pit, formed after the work of the bucket: clean or tamp, as is, and then pour the “pillow”?

FORUMHOUSE participants advised to completely remove all loose soil.

The user also conceived with the help of hired workers to dig a trench (400x600 mm) around the perimeter of the foundation for drainage. Then lay the geotextile and start compacting the sand cushion. It was not possible to dig a trench, due to the lack of laborers ready to do this work.

Because Turkish945 from the very beginning he doubted the need for drainage, he decided to completely abandon it, saving 40 thousand rubles. Although this decision, according to our users, is very controversial, work has continued. Over the weekend, the user, with the help of a friend, took all the loosened soil out of the pit on a garden wheelbarrow.

Turkish945

When you look at the pit from above, it seems that there is very little loosened soil, and for two it is an easy job. As a result, we worked 4 hours without a break and were very tired.

Here's what happened after the removal of the soil.

Also along the way, extruded polystyrene foam was unloaded (19 packs of 120x60x10 cm in size for slab insulation and 2 packs of 1160x580x50 mm for slab sides), which was brought to the site.

Having finished preparatory stage, the user spread geotextiles at the bottom of the excavation and proceeded to form a sand cushion. To do this, he needed a vibrating plate ( Turkish945 rented it), but there was a hitch with the sand.

Turkish945 ordered sand from one "local" seller, who promised that he would bring eight cubic meters of clean sand at a price of 5 thousand rubles for KamAZ. As a result, sand with a large amount of stones and clay was brought to the construction site.

I had to manually sort out and throw out foreign inclusions. The work dragged on into the evening. The user also agreed with two laborers that on Sunday they would come to lay the sand.

Because the ordered sand is not enough, Turkish945, having received a discount for non-conformity for the first truck, he ordered a second car from the same seller, and ordered a third KamAZ with sand, just in case, from another supplier.

On Sunday morning, it turned out that laborers who had been hired the day before were being delayed. In order not to waste a day, the user got to work.

Turkish945

I rammed the sand with a vibrating plate weighing 85 kg. Made 4 passes in total. One pass took 30-40 minutes. Sand spilled with water.

By this time, two trucks with sand had arrived. The first - with sand from the seller, who deceived on quality, but gave a discount and swore that this would not happen again. The second truck is from a new supplier. Having unloaded two heaps side by side, Turkish945 I saw that the sand was again with clay. In addition, the heap, which, according to the first seller, should be 8 cubic meters in volume, looks exactly the same as the heap from the second seller, but who brought 6 cubic meters of excellent sand.

Bottom line: the first supplier has completely exhausted the credit of trust and said goodbye to him. Without waiting for the unskilled workers, who promised to arrive by this time, the user and his father-in-law began to take away the rest of the sand on their own.

To bring the layer thickness to "0", they drove in pegs with marks of the required level.

By order of the charter, Turkish945 I decided to call the laborers again and find out where they were. Having received the answer that they are already on the way, the work continued. As a result, the "assistants" arrived in the evening, and in ordinary clothes, and when asked how they were going to work in this form, they replied: "We only came to see the scope of work."

Having looked around, the guys immediately declared a price of 1000 rubles per 1 cubic meter of sand. This is about 30 thousand rubles. for two, for 2 days of work. Saying "goodbye", the developer refused their services.

After all the ordeals, Turkish945 found the guys who quickly scattered and compacted the sand at a price of 1500 rubles. per day per person. In total, 40 cubic meters of sand were used for the sand cushion.

Turkish945

We compacted the sand to the state of the slab. It turned out a flat and solid base.

The next stage is the marking of routes for engineering communications. For ease of use, the user made a simple device - "beacons", driving into the caps from plastic bottles nail "hundred".

The “beacon” is stuck into the sand, and a roulette ring clings to the nail head.

This allows you to mark the tracks without assistance.

Track lines on the sand were marked with paint sprayed from an aerosol can along a stretched thread.

Having marked the routes, they dug trenches for engineering communications.

The main thing is to observe all the necessary slopes for sewer pipes. 2 cm per 1 running meter for a pipe with a diameter of 110 mm and 3 cm per 1 linear meter for a pipe with a diameter of 50 mm.

Pipes (under water and heating mains) enter the foundation body in a sleeve - a pipe of a larger diameter. In this case, 110 and 160 mm. Moreover, the entrance of the pipes is deliberately made not at 90, but at 60 degrees. To do this, they took and connected two knees with an angle of 30 degrees.

To check the tightness of communications, you can muffle the outlets and pour water into the pipes. If the liquid level does not change, and there are no leaks at the joints, then the routes can be buried.

Having covered the communications with sand and rammed it, the developer laid out the insulation with the displacement of the plates.

Final variant.

Now we move on to knitting the reinforcing cage. To speed up work Turkish945 I ordered rebar, already sawn to the required dimensions.

Turkish945

When I saw the amount of rebar delivered, I realized that I had accepted correct solution. And I saved time, and I saved the tool, because I'm not sure that my "Bulgarian" would have withstood such a volume of work.

A special gun was rented for knitting reinforcement, despite the skepticism on the part of portal users about this expensive equipment.

The most frequent complaints: the battery does not hold, does not knit well, the wire gets tangled, but Turkish945 was pleased with the performance of the pistol. According to him, the wire got confused only at the very beginning - the first 10 minutes of work, then, having "filled his hand", he knitted with a pistol without marriage.

As for the speed of work, it took about one hour to tie the reinforcing cage in increments of 25 cm with smoke breaks. And wire spools, costing 120 rubles, are enough for about 170 knots.

Pursuing independent construction, you need to be prepared for various force majeure circumstances - a sharp change in weather conditions, etc. Arriving at the site one day to finish tying the reinforcing cage, the developer saw the following picture.

The Swedish plate is an insulated monolithic slab foundation of small depth. main feature This technology is that the entire base of the house is based on a layer of insulation (under the stove). Under warm home 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 construction shallow foundations on heaving soils described in Organization standard (STO 36554501-012-2008), developed by the Research, Design and Survey and Design and Technology Institute of Foundations and Underground Structures (NIIOSP) named after. N.M. Gersevanova (FSUE NRC "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 plate" technology combines the device of an insulated monolithic foundation slab and the possibility of laying communications, including a system of water floor heating. An integrated approach allows you to get in a short time an insulated base with built-in engineering systems and a flat floor, ready for laying tiles, laminate or other coatings.

The main advantages of the insulated Swedish plate:

• The construction of the foundation and the laying of communications are carried out in the course of one technological operation, which allows to reduce the construction time.
• The ground surface of the foundation slab is ready for laying the flooring;
• The PENOPLEX FOUNDATION® thermal insulation layer, about 20 cm thick, reliably protects against heat loss, which means a significant reduction in the cost of heating the house 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 problems with frost heaving of the base soils;
• Laying the foundation does not require heavy equipment and special engineering skills.

Mounting Features

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

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

Instructions for use:

• Step 1. Removal of the top layer of soil (usually about 30-40 cm);
• Step 2. Compaction of sand and gravel preparation (coarse sand, crushed stone);
• Step 3. Installation of drainage along the perimeter of the structure and utility pipes;
• Step 4. Laying of side elements and PENOPLEX FOUNDATION® slabs at the base;
• Step 5. Mounting the reinforcing 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 a monolithic slab with concrete mix.

The heating system integrated into the foundation structure provides comfortable conditions indoors. And the use of durable and absolutely moisture-resistant PENOPLEX FOUNDATION® boards as preparation of the base will significantly increase the thermal reliability and efficiency of the underfloor heating system. As a coolant in the system, ordinary water or antifreeze can be used (if winter period time in the room it will not be possible to always maintain a positive temperature). As heating pipelines in water systems warm floors almost all types of pipes can be used: metal-plastic, copper, stainless steel, polybutane, polyethylene, etc.

When laying heating pipes, the following rules are followed:

• Higher thermal power underfloor heating is achieved by more dense pipe laying. And vice versa, that is, along the outer walls, the heating pipes should be laid more tightly than in the middle of the room.
• It makes no sense to lay the pipes more densely than after 10 cm. More dense laying leads to a significant overrun of pipes, while the heat flow remains almost unchanged. In addition, a thermal bridge effect may occur when the coolant supply temperature equals the processing temperature.
• The distance between the heating pipes should not be more than 25 cm to ensure even temperature distribution over the floor surface. So that the "temperature zebra" is not perceived by the human foot, the maximum temperature difference along the length of the foot should not exceed 4°C.
• The distance of the heating pipes from the outer 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.
• Do not lay pipes at the junction of monolithic slabs. In such cases, it is necessary to put two separate contours on opposite sides of the joint. And the pipes crossing the joint must be laid in metal sleeves, 30 cm long.

Underfloor heating pipes must be resistant to damage, as they are subjected to mechanical stress during installation. The best option is products made of cross-linked PE-Xa polyethylene. Photo: StoneHut (2)

How to calculate the thickness of the slab and the cross section of the reinforcement?

In this case, one should be guided by the standards (SP 50.101.2004 and SP 63.13330.2012). An easier way is to use finished projects, which are available from all major construction companies. To check the calculations and compare options, it is worth using special computer programs, such as Foundation, GIPRO, or WINBASE.

On the "classic" Swedish slab, you can immediately build walls by placing two layers of rolled waterproofing under the first crown (or row of masonry). Photo: Stone Hut

Is drainage required around and under the foundation slab?

In swampy and flooded areas, it is highly desirable. At the same time, the function of the draining layer is performed by backfilling of crushed stone of a large fraction (20–70 mm). The system will be more efficient if tubular drains are laid in the thickness of the bedding (their optimal step is 1.5–2 m). A drain is also needed around the perimeter of the slab or blind area. Water should be drained to a drainage well or to a descending relief; when the groundwater level is less than 1 m from the surface, it is advisable to use an automatic system. The presence of drainage will reduce the risk of soil freezing under the house, extend the life of the foundation and reduce the risk of cracking the blind area.

The slab is poured under the entire house, including the porch and terrace (veranda). If you attach these elements later, there is a high probability of the formation of distortions and cracks at the junction of the walls.

How to lay communications?

Water and sewer pipes, as well as an electric cable (if its underground input is provided) are laid when the pillow is installed. They are protected from possible damage with a layer of XPS or wrapped with several layers of waterproofing material. In principle, it is possible to connect to communications even after construction is completed - through a wall-mounted insulated box.

But sometimes a monolithic or masonry plinth is built first. Photo: Foundation 47

Is it possible to build a slab foundation in the cold season?

This is possible, but is associated with an increase in costs and the risk of reducing the reliability of the structure.

Concrete with winter modifiers is 25-40% more expensive than conventional, and the construction of a heated dome, which is indispensable in hard frost, will cost 30-100 thousand rubles. In winter, earthworks are very difficult, and all other tasks are complicated by cold and lack of daylight hours.

The blind area is poured over the drainage cushion and reinforced with a road mesh. Photo: IZBA De Luxe

Is it possible to build a slab foundation from homemade concrete?

Only for a small building for economic purposes. If we are talking about a house, then this method is excluded, because when pouring concrete in small portions, numerous “cold” seams cannot be avoided, which will catastrophically reduce the rigidity of the slab and its resistance to cracking. When delivering ready-made concrete, the interval between the arrivals of automixers should be 3-4 hours.

It is desirable to perform an uninsulated blind area in fragments 1–1.5 m long in order to avoid the appearance of cracks. Photo: IZBA De Luxe

Can the flooring be laid directly on the surface of the Swedish board?

Yes, as a rule, it is possible to do without. In extreme cases, add a thin layer of self-leveling mixture. Note that it is desirable to lay coatings on the Swedish stove that conduct heat well, for example, porcelain stoneware or stone tiles, a special laminate.

On the open terraces a weather-resistant coating with an anti-slip surface is laid on top of the slab, for example, porcelain stoneware or clinker tiles, terrace board from larch or composite. Photo: ShutterStock/Fotodom.ru

3 myths about reinforcement

1. Reinforcement should be knitted, not welded, as welding adversely affects the strength of the metal. In fact, this applies only to alloyed reinforcement, which is practically not used in individual construction. Knitting reinforcement is easier and cheaper, which explains the popularity of this installation method.
2. You can knit reinforcement with anything and not necessarily tightly, since the connections are necessary only for mounting positioning of the frame elements. Meanwhile, according to building codes, when knitting lap and cruciform joints, the rods must be pulled up to each other without a gap. Overlaps (their length is equal to 40 reinforcement diameters) should be tied with steel wire in several places.
3. The diameter of the reinforcement is not important if the required reinforcement ratio is observed (the ratio of the cross-sectional area of ​​the reinforcement to the cross-sectional area concrete structure). In fact, the use of thin reinforcement (8 mm) increases the complexity of installation and complicates the quality control of the work performed.

In private construction, it is advisable to increase the reinforcement coefficient by at least 20%, compared with the recommended standards, and use high-quality concrete.

Design option for insulated slab foundation

1 - sand and gravel pad; 2 - insulation (EPS boards); 3- drainage pipe; 4 - reinforcement cage; 5 - pipes of the floor heating system; 6- flooring(tile); 7 - drainage membrane; 8 - ; 9 - gravel backfill; 10 - moisture resistant finish. Photo: TechnoNIKOL

The underfloor heating system is tested in two stages. After the installation of the pipeline and before pouring the concrete slab, the integrity of the pipes is checked by a liquid pressure that is 1.5 times the working pressure. The duration of the test is 3 hours. As an exception, if a hydraulic test is not possible (for example, due to frost), a test with compressed air is allowed. When pouring concrete, the pipes must be filled with cold coolant and be under pressure (working or test). After the concrete has gained the required strength, a thermal test is carried out, which lasts seven days. First during three days a coolant heated to 20–25 °С should circulate in the system. Then set the maximum working temperature, which is maintained for four days. During this period, the uniformity of heating of all circuits is checked using a contact thermometer.

Sergey Bulkin

REHAU expert

Enlarged calculation of the cost of building an insulated slab foundation with an area of ​​80 m2

Name of works	Quantity	Cost, rub.
Geodetic stakeout		12 000
Earthworks, pillow device		16 800
Drainage devices		18 000
Plumbing and sewer pipes		14 500
Installation of formwork, insulation, reinforcing cage		32 000
Installation of underfloor heating pipes		34 200
Concreting, vibroconcreting		26 000
Total
Applied materials by section
		14 500
Granite crushed stone	8 m3	16 000
Edged board		3500
Pipes (PVC and polypropylene)	Set	22 000
Rebar (bar 12 mm and mesh 8 mm)	1.1 t	32 000
XPS sheets CARBON ECO SP 1180 × 580 × 100	235 pcs.	79 900
Gaskets and fixing materials		7 500
Concrete M300	13 m3	44 200
Total
Total