Among the shallow foundations, the foundation slab is considered the most durable and reliable. As another advantage, a relatively small amount of excavation is indicated, but this common feature all foundations with a shallow occurrence in the ground. The only drawback is the high cost of materials and work, which is due to the large volume of concreting and the need to create reinforcing cage throughout the base area. But in principle, it is no more expensive than a buried strip foundation, especially if you also take into account the concrete floors on the ground of the basement.

Foundation-slab allows you to build a house on the sand

Scope and features of the calculation

The main purpose is to use as a base on soft soils with a limit value of bearing capacity up to 2.5 kg / cm2. This includes sands - silty and medium density, plastic clays and loams, peat and moist soils. Moreover, it is the level of soil moisture that largely determines its bearing capacity - when wet, it literally “floats”, losing its strength properties. Therefore, drainage, waterproofing and blind areas play an important role in the arrangement of this type of foundation.

Reliable waterproofing is an important component of any foundation

As one of the advantages, the argument is often cited that a monolithic slab can be made by hand. But even if we do not consider the issues of choosing the type of concrete and the parameters of the reinforcing cage, there remains such an important stage as calculating the dimensions of the slab. And if there is a certain clarity with the area (the size of the house plus a small margin on each side), then it is not easy to calculate the thickness of the slab.

But this range also includes “light construction” in the form of a garage or a summer kitchen, and a two-story house with an attic. If the slab is not “thick” enough or the wrong thickness of reinforcing bar (or mesh size) is chosen, then it will not be able to withstand the total load. An excessive margin of safety leads to an increase in the cost of an already expensive foundation, and an excess amount of concreting will make the entire structure heavier, and the soil may not withstand the total load.

There is another option with a diametrically opposite scope - the slab is equipped on rocky and coarse-grained soils with very high bearing properties. In this case, it rather levels the site for construction, and does not redistribute the load from the structure.

Another feature of this foundation is that the laying of pipelines must be done at the stage of the zero cycle.

What is taken into account when calculating the foundation

When calculating the foundation "monolithic slab", the total load is taken into account, which includes:

• weight of the building, including finishing materials;
• the weight of the plate itself;
• engineering systems equipment;
• communications;
• furniture and household appliances;
• wind and snow pressure.

Atmospheric loads are temporary in nature, but they are taken into account as permanent. They are defined as statistical characteristics given for each region in tables normative documents. They cannot be neglected - in some areas, wind loads and snow pressure are of great importance, and in terms of a square meter of base, they are comparable to the specific gravity of equipment, household appliances and furniture.

Such a layer of snow is a serious test for any home.

"Amateur" developers practice a simpler method for calculating the thickness of the slab. He proceeds from the position that a double mesh reinforcing frame is necessary for a low-rise building. The distances from the lower and upper surfaces of the plate to the reinforcement are taken equal to 50 mm, the distance between the belts is more than 70 mm, the diameter of the bar lies within 12-16 mm. And the calculation formula is reduced to the following amount: 2x50 + 70 + 4x (12-16) \u003d 218-234 mm. And since the thickness is rounded up to a multiple of 50 mm, it turns out that it is equal to 250 mm. The bearing capacity of the foundation is finally “regulated” by choosing the diameter of the reinforcement and the brand of concrete.

But it must be emphasized once again that this is a very approximate method, and in some cases it may not “work”, so all calculations should be carried out by specialists.

Video description

An example of a full-fledged calculation of the foundation slab for a house in the video:

Types of slab foundation

There are two types of foundation-slabs according to the execution technology: prefabricated and monolithic.

In the first case, reinforced concrete slabs are laid on the prepared site. And as a leveling and "bonding" layer, a cement-sand screed is poured. The bearing capacity of such a foundation is low, so it is either built on rocky (or coarse) soils, or for light buildings.

A monolithic slab does not have any disadvantages and limitations in use, except for the high cost of manufacturing. There are even recommendations for the use of a deep slab foundation:

• for heavy structures on bulk soils with deepening to the mainland soil;
• construction on mixed soils with different bearing properties;
• for the arrangement of the basement in conditions high level ground water.

According to the profile, there are three options for the foundation:

• Solid plate. A house without a plinth, when the surface of the slab serves as the subfloor of the first floor (for example, a Swedish stove). It can be both monolithic and combined.
• Ribbed plate. At the bottom there are stiffening ribs. If this is a monolithic technology, then additional trenches are dug for them, and the formwork and reinforcement are combined with common part. If this is a prefabricated technology, then ribbed ready-made slabs are used for the foundation.

Additional stiffening ribs will make the structure more reliable even with a small thickness of the main part of the foundation

• Box foundation. House with a plinth on a stove and concrete floor first floor. The slab and plinth can have a monolithic technology, prefabricated or combined.

Structure by layers

This is how the most complete structure of a monolithic slab looks like as the base of the house

A standard full profile pie looks like this:

• leveled and compacted "mainland" soil;
• separating geomembrane (desirable, but not required);
• pillow of sand (or two layers - sand and gravel)
• footing;
• waterproofing;
• sheet insulation;
• base plate.

In Europe and in our Lately the modification of the foundation, which is called the "Swedish plate", is gaining popularity. The peculiarity is that a warm water floor is laid not in the screed, but in the slab itself.

Swedish foundation slab a private house with underfloor heating

Drainage and waterproofing

The main reason for the wetting of the soil and the loss of its bearing properties is not groundwater, which lies much deeper than the sole shallow foundation, but in the upper water. This includes precipitation, seasonal snowmelt, and water infiltration from nearby bodies of water if their "mirror" is at the same level as the plate. To a lesser extent, but also affects the capillary rise of water in some types of soil.

The nature of drainage measures depends on the characteristics of the region and site. If the house is on a slope, then it is possible to lay a cut-off drainage. On flat areas, you can equip a complex storm sewer, including the removal of water from the sites and paths outside the site. But in any case, below the level of the concrete foundation slab along the perimeter, the blind areas are laid drainage pipes, which, with a slight slope, are reduced to a drainage well.

Drain pipe laying

Waterproofing is complex. To briefly formulate the essence of the technology, it lies in the fact that the plate is literally wrapped in two layers of rolled insulation. And the full list of works looks like this:

1. After carrying out the zero cycle and backfilling the sand and gravel pad, two layers of rolled bitumen insulation sheets are laid on the leveled area.
2. All sheets are overlapped, and the top layer relative to the bottom is shifted by a width of half a sheet.
3. Along the entire perimeter, rolled waterproofing should be laid with a margin sufficient to bend the edges to the end of the slab.
4. After pouring and maturing of concrete, the protruding edges of the waterproofing are glued with bitumen to the end of the base.
5. Carry out waterproofing work to protect the upper and side surfaces of the foundation

Video description

Visually all the stages of work on the video:

In conclusion. Whatever they write about the possibility of arranging their own hands monolithic foundation-slab, its construction technology suggests even for small house a significant amount of concreting with a continuous pouring cycle. And with a foundation thickness of 25 cm and a modest house size of 10x10 m, this is 25 m3 of concrete. And this is without taking into account the concrete layer. Plus you need:

• carry out a zero cycle;
• make drainage;
• deliver, level and compact for a pillow at least 30 m3 of sand and gravel;
• competently carry out waterproofing of the slab;
• mount the formwork;
• tie two grids of the reinforcing frame.

Only a team of professionals can qualitatively perform such a foundation project for a house.

In our time, when the field of building materials is rapidly developing, there are many types of foundations that differ in characteristics, type and purpose. But recently, among professional developers, it has become more and more in demand - slab foundation. This type is especially convenient for owners of plots with land in poor condition. And also, this option is considered one of the available. Even an inexperienced person in repair matters can pour the foundation slab on their own, without putting much effort.

Areas suitable for slab foundation applications

The most main feature slab foundation - a shallow base, which is made of a concrete pad. This property allows you to fulfill its purpose even on moving soils. Any other type of foundation will be covered with cracks during the movement of soils, therefore, in such areas it is necessary to use exclusively slab foundations.

This base is perfect for building houses where hard materials are used. It prevents deformation of the structure.

Buildings that have low, in comparison with the ground, floors, must be erected using exclusively slab foundations. When using it, there is no need to build a basement and grillage.

Slab foundation advantages and disadvantages

Before you start choosing a particular product, you need to weigh all its pros and cons. Let's start with the positive qualities of the slab foundation:

• It is reliable and durable. And it's hard to argue with that. Interview specialists who are versed in building materials, and all of them will say that tiled is the most reliable type of foundation.
• It has a large area of ​​\u200b\u200bsupport on the ground, and if it is laid correctly, the soil will not adversely affect the foundation in the cold season.
• The slab foundation is universal. The fact is that the technical characteristics that it possesses allow it to be laid on almost any soil. Therefore, they are most often used this species in areas where no other foundation could cope with the task.
• The ability to establish a foundation above the depth of freezing of the earth. This plus was made possible thanks to the massive sand and gravel cushion, which prevents the impact of the soil in the cold winter.
• A high level of rigidity, which prevents the house from sagging, and if this happens, then the room will not be significantly damaged.
• No need to install a subfloor.
• The ease of device technology, which allows you to do the work on your own and save on the services of a master.
• Suitable for any type of low-rise building. The only thing to consider is the thickness of the slab (the lighter the room, the thinner the slab).
• Can withstand ground movement. It is possible to build a house on floating lands, since the tiled foundation will not burst and tear, but simply begin to move along with them. This property is to keep the building intact.

It should be borne in mind that all the previously listed advantages will be valid only if the installation rules are strictly observed. If there are violations of technology during the laying process, then the pros can turn into cons.

As with any foundation, there are some negative qualities:

• One of the biggest downsides that buyers point out is the price. The high cost is justified by the large amount of concrete, reinforcement, sand, and crushed stone, unlike analogues. But on the other hand, the money spent quickly pays off. The tiled foundation will not need frequent repairs, costly maintenance, moreover, it will function as the floors of the first floor, which will also reduce costs.
• It is not recommended to lay a tiled foundation under the house, which is located on a site with a large slope. In this case, the output will be leveling the ground level, or installing ground floor, but it's quite expensive.
• There are difficulties with the construction of the basement. In the case of building a basement, you will have to fill in a monolithic slab under it, which will cause significant losses to the owner.
• The occurrence of difficulties during the installation of the foundation in winter days. To pour concrete in sub-zero temperatures, you will need to spend money on heating it and maintaining the warmth around it.
• Difficulties in wiring communications. Consideration should be given to the location of plumbing, electricity, etc. before the start of pouring concrete because after that it will be impossible to do this.

As you can see, the slab foundation has a large number of advantages, and disadvantages can be circumvented, however, this will cost additional costs.

Material calculation

Before starting work, it is necessary to calculate the slab foundation: the dimensions of the formwork, the number and diameter of the reinforcement, the volume of concrete. All these values ​​can be found using a special calculator. To do this, you will need to enter the brand of concrete, the width and length of the slab (in meters) and its height (in cm). Further, the program itself will calculate the amount of materials necessary for arranging the foundation.

Types of slab base

Also, before starting work, it is worth deciding on the type of tiled base. There are several options. The main ones are:

• ordinary concrete pad;
• tape-slab.

This type is used during the construction of buildings with a basement. A hole is dug, a concrete pad is placed, on which the base is subsequently installed. The entire load is placed on the strip foundation.

• base with stiffeners;

It is the best option among all, because it has high strength. Its construction requires more materials and effort, so its technical characteristics are superior to other types of foundations.

Preparation of materials and tools

Preparatory work also includes the assembly of a set of materials:

• concrete;
• steel bars;
• gravel;
• sand;
• material for waterproofing (geotextiles are most often used).

You will also need some tools for the slab foundation:

• saw;
• hammer;
• shovels;
• transport wheelbarrow;
• apparatus for welding;
• Bulgarian;
• roulette.

Construction of a slab foundation

Instructions for the construction of a slab foundation includes several stages:

1. First of all, we carry out geological survey land, we determine places with strong elevation differences.

2. We mark the future base.

3. We remove the soil layer and level the area where the construction will be carried out.

The choice of the depth of the pit directly depends on the type of structure (shallow or swollen). If we consider a shallow foundation, then it will be enough to remove 50-70 cm of earth. The dimensions of the pit are selected taking into account that they should be 1-2 meters more than the length / width of the foundation. After digging, be sure to compact the soil.

4. We design and install formwork (strong wooden boards are suitable for its construction).

5. We dig several trenches in the pit and lay waterproofing in them.

6. We lay plastic pipes on top of the waterproofing.

7. We fill the bottom with a mixture of sand and gravel, evenly distribute it and tamp.

8. We assemble a double reinforcement cage and tie it with a special wire.

For reinforcement, only rods with ribs are suitable. They will provide high-quality adhesion of the frame and concrete mix, as well as prevent stretching of the foundation slab. Using smooth rods in the work, the base will crack at the first subsidence of the soil. The reinforcement is laid in increments of less than 30 cm. If you increase the distance, then the strength of the base will decrease significantly.

9. We put plastic pipes in places where various communications will be located.

Before installing them, it is necessary to fill them with sand and carefully compact the backfill. Pipes must be laid before pouring, since it is forbidden to make holes in concrete.

10. Fill the monolithic slab with concrete mortar.

The slab foundation is poured immediately. The concrete solution must be kneaded once and a large amount, so that it is enough for the entire pour. The work is quite laborious, so ideally it should be done by four people. We lay the concrete in uniform, horizontal layers. It is necessary to fill in such a way that the plate does not have deviations from the horizon. To prevent such slopes, we create stiffeners in the lower part. These are strips of concrete, made in the shape of a trapezoid. The last layer must be poured very quickly. Use a mixer or concrete pump for this.

11. Carefully smooth and level the surface.

12. We cover the resulting foundation with a film and leave it for a couple of weeks. Do not forget to moisten the construction during the first five days.

How to mix concrete for the foundation?

To reduce the cost of work, you can knead concrete at the site of the foundation with your own efforts. But in this case, you will need a special concrete mixer. It perfectly mixes all the components without forming lumps. This unit operates at a power of 250 watts or more. At one time, you can get from 50 to 250 liters of solution. But the quantity greatly affects the time of work. If we take a small device as an example, then it will take about 5 hours to create 1 pour cube.

An important point is the location of the concrete mixer, it should be located near the base. This will reduce the amount of force you apply.

Of course, there is an option to independently knead concrete for a slab foundation using a shovel, but this will greatly affect the quality of the future foundation.

Warming

Of course, the best option would be to insulate the foundation to achieve a warm indoor temperature all year round. To do this, use various heaters. The most popular among them is foam. Only 10 cm layer will be enough.

Also, there are different types insulation. We recommend using the subfundamental. Insulating material is placed directly under the stove.

Use the tips below to make your job easier:

1. To create a quality foundation, you need to use only durable reinforcement and concrete mix.

2. The use of a shallow base will reduce the cost of building materials by approximately 35-45% of the cost of an underground room.

3. It is very important to consider the thickness of the slab. For example, choosing a base thickness of 20 cm, you will need to "reinforce" in some places where there is too much load. At 25 cm, it becomes possible to knit a frame of reinforcement uniformly, without resorting to additional reinforcements. A 30-centimeter thickness will help increase the strength and durability of the foundation, but at the same time it will make you spend a lot on concrete.

4. During the manufacture of a cushion of sand and gravel, the material must be laid in layers. One layer should not exceed 12 cm. After each masonry, carefully tamp. If your pillow will consist entirely of sand, be sure to moisten the layers.

5. Before laying the insulation material, the pillow must be covered with a dense polyethylene film to prevent water leakage from the concrete solution. It is advisable to glue or solder the polyethylene at the joints, or overlap the sheets.

After reading this article, everyone will be able to make sure that the construction of a slab foundation is a fairly simple process and is possible when creating it yourself. The main thing is to follow all the rules of pouring and construction technology. If this is done, then your foundation will serve faithfully for many years.

Also, we suggest watching a step-by-step instruction on how to properly build a slab foundation. The video is located after the article.

Using a monolithic reinforced concrete slab as a foundation is an expensive pleasure. However, there are a number of conditions under which this is the only correct option.

On construction sites with fragile soils, for example, only in this way can the reliability and stability of the structure be ensured.

Despite the frightening size of the structure, it is easy to build with your own hands - step-by-step instruction this process is shown below.

To build a slab foundation with your own hands (), you must first prepare a set of necessary tools and building materials.

So, you will need:

• bayonet and shovel: their number will depend on the number of assistants who will work with you;
• building level;
• vibrating plate;
• cord or twine for marking. To perform this operation, pegs will also come in handy;
• vibrator for compacting the concrete mixture during pouring
• concrete mixer (you can order ready-made concrete, but in this case it is necessary to organize an access road to the foundation site);
• hook for knitting a reinforcing cage.

It is possible to determine the required amount of basic materials only after carrying out the necessary calculations.

The "pie" of the slab foundation consists of the following layers:

• gravel - sand cushion;
• waterproofing layer;
• reinforcing cage filled with concrete.

Usually, with their own hands, a slab foundation () is erected for private houses or outbuildings. All of them belong to light structures or moderate.

In such cases, complex calculations can be avoided by taking the thickness of each layer based on the recommendations of specialists ():

• monolithic reinforced concrete slab - at least 100 mm;
• sand layer - 300 mm;
• crushed stone bedding - 100 mm.

Knowing the thickness, width and length of the foundation, by simply multiplying these values, you can calculate the cubic capacity of each of the basic materials.

The situation with the calculation of the amount of reinforcement is a little more complicated. It is used for the manufacture of reinforcing cage. This design consists of two grids interconnected by vertical segments.

In private construction, reinforcement with a diameter of 12 mm is used to assemble the upper and lower belts of the frame. The mesh pitch is 200 mm. To calculate the footage of the reinforcement, it is necessary to calculate the number of rods and multiply the result by the length of one of them.

Divide the length and width of the future frame by 200 and add one rod to the resulting number. It remains to multiply these numbers by 2 (the number of belts), and then by the length of the rod and add the results.

Example: you need to mount a frame with a size of 6000x4000 mm.

(24+1) x 2 x 4 (m) = 200 m;

(16+1) x 2 x 6(m) = 204 m;

200 + 204 = 404 (m.p.)

Convert linear meters to tons:

404 (m) x 0.88 (kg / m) \u003d 355.5 kg \u003d 0.356 t,

Where 0.88 kg / m is the specific gravity of one linear meter of reinforcement with a diameter of 12 mm.

The optimal frame height for private buildings is 150 mm. Based on this, it is possible to calculate the number of reinforcement with a diameter of 8 mm to perform vertical connections.

Binding wire takes on average up to 20 kg per ton of reinforcement. That is, for our example, it will require no more than 7.2 kg (20 x 0.356 = 7.12).

When calculating the amount of concrete, it must be taken into account that the reinforcement must be completely covered with a concrete mixture with a layer of 50 mm. Therefore, the thickness of the slab for a frame with a height of 150 mm will be 250 mm.

Stages of work

Maybe you will do the best choice foundation for you.

Do-it-yourself video slab foundation.

Today, for the construction of buildings with one or two floors, several types of foundations are used. The most popular screw base, shallow and pile foundation. However, when building a dwelling on complex and heaving soils savings on the most important part of the house - the foundation, can lead to even greater financial waste later in its operation.

Thus, recently, more and more often, a solid monolithic slab is being laid in the foundation of the premises. The pleasure is not cheap, but the option to save money still exists. To do this, you can build a monolithic base yourself, and you will learn how to properly make a slab foundation with your own hands from our step-by-step instructions.

Aspects for

Probably one of the biggest benefits monolithic construction consists in the fact that even on loose and heaving soils, a building erected on this type of foundation will not be subjected to deformation and various damages associated with subsidence of the soil. So, non-buried and shallow monolithic foundations erected on a pillow of non-porous materials show themselves well.

Buildings made of the following building materials are most susceptible to deformation:

• Cellular concrete;
• Expanded clay concrete;
• Cinder block and brick.

A monolithic reinforced slab will require considerable financial investments, but will pay off in the future, because with its proper construction, you will no longer need to repair work throughout its entire operation. To all of the above, its manufacture does not cause any particular difficulties, and this instruction will be enough for you. If you still have questions, you can watch a video showing the process of building a floating foundation step by step (due to its design, this type of foundation “floats” on the upper layers of the soil, which is another definite plus).

Aspects against

As we have repeatedly repeated, the main disadvantage of a monolithic base is its cost. But, we emphasize, saving on the support of the entire structure is not a noble cause, because there is a huge risk of going broke on repair work in the future.

The second aspect of the “against” is the inability to move the house to another place with a foundation. For such purposes, a pile foundation is best suited, which in any such situation can simply be unscrewed, transported, screwed in and put on it. frame house again.

Determining the thickness of the slab

Depending on the properties of the soil on which you are going to build a monolithic base, the thickness of the concrete slab of the future foundation is determined. From individual characteristics soils depends on the maximum load that they, in turn, can withstand.

To determine how much pressure a structure will create on the soil, you need to have the following data:

• Mass of reinforced concrete base (solid slab);
• The mass of material for the construction of structures on the foundation;
• The mass of the payload in the house;
• Precipitation weight in different seasons.

Considering the practice of the entire existence of this type of foundation, for small-sized structures (summer kitchen, garage, shed), a monolithic slab 100 mm thick is quite enough. When erecting a dwelling, the thickness of the floating foundation is increased by 2.5 times, which allows for reinforcement in several layers.

We protect the foundation from groundwater

If you want the foundation of your house to last a hundred years, or even more, you need to protect it as best as possible from groundwater, which adversely affects the structure and integrity of the foundation. The following works will thoroughly protect the foundation from moisture and water underground:

• The foundation pillow is protected from groundwater with rolled material. They must be laid out on top of a non-porous cushion of sand and gravel. Lay waterproofing rolls overlapping, while the edges should go beyond the boundaries of the future base, which will subsequently organize the insulation of the ends on the side;
• Bituminous coating will serve as a good insulator from water side surfaces monolithic base;
• From above, the floating foundation is protected with the same bitumen mastic or rolled material.

Along with waterproofing, thermal insulation, which is mounted on top of the floating foundation before laying the leveling screed, will help to provide a comfortable atmosphere to the living space.

Backfilling guarantees the safety of the monolithic base during its construction on heaving soils, and the concrete pavement will become a barrier between rain and melt water and the base.

Getting Started

There are two different ways slab foundation construction:

1. The first method is to assemble a monolithic foundation from several independent reinforced concrete slabs. plate type in this case does not matter, so both road and airfield plates can be used. This method of building a foundation is fast, because. the prepared materials are placed next to each other as tightly as possible on a previously leveled and compacted platform under the base. The site, in turn, is a recess, inside which a pillow of sand and gravel was laid (during the process of laying the pillow, it is poured with water and tamped) and covered with a layer of waterproofing for reliable protection foundation from groundwater.
2. The second method is the erection of a slab foundation manually in the form of a monolith from a concrete mixture.

Preparatory and ground works

Preliminary work includes, first of all, taking soil samples. This is followed by cleaning the building spot from the top layer of soil and transferring the building plan to the cleared area. After that, according to the markup, a recess is prepared for pouring concrete into it. Due to the not impressive thickness of the monolithic base, digging a foundation pit for the foundation will not be a difficult task (you can handle it with an ordinary shovel and save on attracting special equipment).

We install the formwork

Various materials are suitable for the construction of formwork, but the best option has been and remains a planed board with a thickness of about 20 mm. We fix pre-knitted shields around the perimeter of the building and securely fasten them with slopes and posts.

Inside the formwork itself, before the start of subsequent work, pipes of the water supply and communication system are laid and taken out of the wooden frame. This procedure will not tolerate haste, because in case of incorrect calculations, you will have to hammer a cast concrete base.

"Metal Skeleton"

A metal belt made of reinforcement is capable of preventing the destruction of a monolithic base and giving strength to the structure. Lay it inside the formwork. The diameter of the reinforcement is influenced by many factors, but on average it is 12 mm. The bars at the intersections bind knitting wire. As an alternative, building plastic clamps are often used. In addition, there is an option to fasten the bars with spot welding, here it’s an amateur.

Intersecting, the reinforcing bars will create some cells, the width and length of which should lie within 30-40 cm. The reinforcement frame consists of two such grids, which are connected to each other by vertical bars. Their length directly depends on the thickness of the monolithic base. It is necessary to lay the finished frame in such a way that there is a distance of at least 5 cm between it and the edges of the foundation. This can be achieved by adjusting wooden bars of the same height under the bottom.

Dealing with concrete

In order for a monolithic foundation to have characteristics that will meet all high requirements, concrete grade 300 (with a strength of 3 centners per 1 sq. cm) should be used for its manufacture. Frost resistance should be at least 200, moisture resistance and mobility - 4 each.

The filling process should take place in one sitting. It is not recommended to pour concrete in several crane passes. After the recess is completely filled and the concrete mixture reaches the required height, it is treated with building vibrators. This event is aimed at eliminating air cavities in the solution.

During drying, it is necessary to periodically moisten the concrete casting of the foundation, because there is a risk of cracks due to drying. It can also be covered with insulating material after pre-wetting with water. On this, the construction of a monolithic foundation can be considered completed.

Video on the installation of the foundation "from and to":

Among all types of foundations chosen by private developers for the construction of their country houses and outbuildings, the undisputed leader in terms of frequency of use are bases. However, quite often the specifics of soils at the construction site, the climate in the region, the location and dynamics of changes in underground aquifers require an excessively deep laying of the sole of the strip foundation, which makes it an unprofitable solution, especially when it comes to building a relatively small in size and total mass building. We have to look for other, more economically justified, but at the same time options that are not inferior in terms of bearing capabilities.

One such solution can be a monolithic slab, poured under the entire future building. The uniform distribution of the load falling on such a foundation over the entire considerable area makes it possible to use such a scheme on soils with a low bearing capacity. And the comparative simplicity of the construction of such a foundation makes it quite feasible on our own. So, the topic of this publication is the foundation slab with your own hands, a step-by-step instruction, from calculations to practical implementation.

General information about the foundation - a monolithic slab

Typical scheme of a monolithic slab foundation

A slab foundation does not require a deep occurrence, rather, on the contrary, its bearing capacity and “floating” features will appear precisely when it is close enough to the ground surface. In this case, even frosty heaving of soils will not have a destructive effect on the stability of the building - the slab itself, with its high-quality construction, together with the building erected on it, seems to “float” on the surface of the soil.

The schematic diagram of the device of a monolithic foundation slab is shown in the illustration below:

1 - Compacted soil - the bottom of a pit dug under the foundation.

2 - A carefully compacted "pillow" of sand, sand and gravel, gravel, which contributes to the uniform distribution of loads, becomes a kind of damper that softens the impact of ground vibrations. Layer-by-layer backfilling and tamping of such a “cushion” is practiced, with one or another alternation of materials, or homogeneous, using ASG.

3 - A layer of geotextile (dornite), which will give the sandy "cushion" a kind of "reinforcement", prevent it from silting or blurring on waterlogged soils. This illustration shows only one of the options for placing a geotextile layer, however, their number and position may vary, depending on specific conditions. So, often such a layer is placed between the surface of the compacted bottom of the pit and the first layer of sandy "cushion" - to prevent the penetration of soil particles into it. A layer of geotextile also separates the sand and gravel layers of the backfill - again for reasons of reinforcement and exclusion of interpenetration. At the same time, the location of the gravel or crushed stone layer above the sandy one seems to be more optimal - because the capillary "sucking" of ground moisture from below is almost completely excluded.

4 - A layer of so-called concrete preparation. This element of the general "pie" of the slab foundation is often neglected for reasons of saving material and reducing the overall duration of the work. Meanwhile, such concrete preparation plays a significant role - it allows you to reach the “clear geometry” of the base for further pouring the foundation or laying insulation materials, makes it possible to mount the hermetic waterproofing that is mandatory for the slab with high quality.

5 - The already mentioned layer of a waterproofing layer that is mandatory for such a foundation slab, protecting the base of the building from moisture from below. The optimal solution is at least two layers of polymer-bitumen-based roll waterproofing materials.

6 - The monolithic slab itself with the calculated thickness.

7 - reinforcing belt of a concrete slab. Its classic design is two levels of reinforcing bars interconnected to give volume to the structure with special clamps. The location of the reinforcement is planned in such a way that a concrete layer of about 50 mm is created between the bars and the edges of the slab from above, below and from the ends - in order to exclude the start of metal corrosion processes.

This - general scheme, but there are also several varieties of monolithic foundation slabs used depending on certain specific construction features.

The simplest and probably the most common option is a solid slab, the uniform thickness of which is observed over its entire area.

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It is this scheme that is most often chosen when erecting houses and outbuildings on fairly stable soil. However, it has an obvious disadvantage - the thickness of the slab is usually small, and it is partially located below the ground level, that is, the upper edge is located close to the ground surface, which is not very good for wall structures. It is not economically feasible to increase the thickness of the slab because of this, which means that another option can be considered - pouring the foundation with reinforcing stiffeners, which have some similarities with the strip foundation. Moreover, these ribs can be located both above the plate and below it.

So, a kind of socle-grillage can be obtained if, simultaneously with the slab, stiffening ribs protruding above the surface of the slab, which is obtained as a “bowl”, are also poured. Such grillages are placed along the lines of the construction of the load-bearing walls of the house structure - after waterproofing their horizontal surfaces, it is from here that the masonry begins.

A similar scheme is still often practiced in cases where it is planned beneficial use basement or basement floor - the slab simultaneously becomes the floor of these rooms. And from the grillages, at the same time, they begin to lay the basement.

If there is no desire to deepen the slab too deep into the ground, and at the same time achieve its maximum bearing capacity without thickening, you can apply a scheme in which the stiffeners are located facing down.

When preparing the surface, installing the formwork and reinforcing frame, recessed “channels” are immediately provided, which, after pouring the slab, will turn into stiffeners facing the ground.

This also turns out to be a kind of "symbiosis" of slab and strip foundations. Stiffeners are planned under the outer walls and capital internal partitions. Well, if there are no internal partitions, then the ribs should be parallel to each other and to the shorter side of the perimeter of the house, with a step not exceeding 3000 mm.

Such a scheme allows to achieve serious savings in concrete, since with properly planned stiffeners, the thickness of the slab can be significantly reduced, by 100 ÷ 150 mm, without losing its bearing potential, and this is, after all, 1.0 ÷ 1.5 cubic meters of mortar for every 10 square meters area.

In addition, ample opportunities open up for warming the foundation slab - the same height difference on the main surface and on the stiffeners is often performed by laying a durable thermal insulation material, for example, extruded. By the way, it is this approach that is the key condition for the construction of one of the improved varieties of slab foundations - the so-called "insulated Swedish slab".

Insulated Swedish stove (USHP) - the basis for houses with minimal energy consumption

The tendency to build houses with minimal, zero or even negative external energy consumption, widely used in modern world construction, leads to the emergence and development of innovative technologies, which include UWB. The main nuances are discussed in detail in the corresponding publication of our portal.

It makes sense to make one more remark. Slab foundations can be not only completely poured, monolithic, but also prefabricated, consisting of ready-made reinforced concrete structures. It would seem that this is much simpler, however, the lack of a rigid connection between adjacent plates makes such a base unstable to possible ground vibrations. For this reason, such a scheme is not widely used, and is practically not used in residential private construction. The only exceptions are small outbuildings, the area of ​​\u200b\u200bwhich is limited by the size of one standard slab, but this, you know, is extremely rare.

Application of slab foundation. Its main advantages and disadvantages

The use of a slab foundation will be fully justified in construction sites that are characterized by soils with reduced bearing capacity. It is usually resorted to where simpler schemes, such as a shallow belt or columnar, are simply impossible due to the peculiarities of "geology": the tendency of soils to frost heaving, horizontal "shifts", close location of aquifers, etc.

In addition, such a foundation, with carefully carried out calculations and design, can become a very reliable basis for multi-storey construction. Uniform distribution of loads on large area foundation gives very low pressure on the ground even during the construction of massive buildings and engineering structures. Indeed, this applies more to construction work carried out on an industrial scale.

About the advantages and disadvantages of the slab foundation, by the way, both real and, frankly, far-fetched, there is a lot of controversy. Let's try to list them and understand a little about this issue.

What they say about virtues ?

• There is a widespread opinion that a monolithic slab foundation is an absolute "panacea" for all cases, that is, it can be built on any soil at all. Allegedly, such a slab of a house, even in a swampy area, will be a reliable basis for a heavy building, since due to its “buoyancy” it will begin to oscillate along with the movements of the soil without being deformed.

It is certainly impossible to agree with such a statement. Most likely, it would be more correct to say only that the slab foundation opens up expanded possibilities for construction in areas with difficult soils, with insufficient bearing capacity for the tape base, with average heaving rates.

But on obviously swampy, waterlogged soils, with the likelihood of subsidence, especially in regions with a harsh winter climate, only a pile foundation will probably become a reliable foundation, for years the piles are driven (screwed) into dense, bearing rocks located significantly below the freezing level.

And the slab foundation, located practically on the surface, can indeed move within certain limits along with ground vibrations, that is, “float”. But the trouble is that in areas with pronounced soil instability, these vibrations can have a very high amplitude, and are applied unevenly to the surface of the slab from below. Even if the soil is absolutely homogeneous over the entire area, this unevenness is explained by banal reasons - on the south side, freezing almost always goes to a shallower depth, and thawing in spring occurs much faster. And this means that the plate willy-nilly will experience enormous internal bending stresses.

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extruded polystyrene foam

As a rule, slab foundations have a very significant margin of safety, and, perhaps, the slab itself will withstand such loads, it will not crack, but small linear deformations are quite likely. They will certainly be transferred to the walls, and in addition, the roll of the entire building from the vertical axis is not excluded. For wooden buildings, it may not be so critical, due to a certain mobility of the structure. But the stresses on rigid stone (block) walls increase with height, that is, with the lever of force application. And it is possible that somewhere in the upper region of the wall a crack will suddenly appear and begin to expand.

So, if you think objectively, you should not overestimate the versatility of the slab foundation - it would be reckless. In any case, if there is no certainty of unconditional success, it would be more expedient to invite specialists to conduct a geological analysis of the site. In addition, it is always useful to get acquainted with the "history" of the use of slab foundations in the surrounding area - what and how long the houses were built on them, what is the depth of the foundation and the thickness of the slab, are there any complaints about the operation, how did the buildings survive seasonal ground fluctuations - these and other questions help you make the right choice.

• Slab monolithic foundations make it possible to build large, even multi-level houses built from heavy materials.

This is true, and many multi-storey buildings in major cities stand on the same basis. In terms of its ability to evenly distribute the load over a large area, such a foundation has no equal. Of course, all this is true with professionally carried out calculations, taking into account the characteristics of the building site, and high-quality performance.

So the conventional wisdom is that a slab foundation is only suitable for small compact houses, and that “his age is short”, limited to 35–50 years – this is nothing more than fiction. We repeat - everything depends on competent professional calculations and on the quality of execution in accordance with the project.

• The construction of a slab foundation minimizes the work of digging a pit - no deep penetration into the ground is required.

If we talk about a slab located on the surface of the soil or with a slight depth, then this is true - only the top fertile soil layer is removed, and the depth of the pit is largely determined by the estimated height of the sand and gravel cushion. True, if this depth is also multiplied by the entire area (and the slab must be laid wider than the future building, and even plus insulated blind areas), then the volume of the selected soil can still turn out to be considerable. So this advantage is very non-obvious - with a shallow strip foundation, sometimes it is simpler in this regard.

Well, if you plan to use a deep monolithic slab, that is, to create a house with a full-fledged basement on its basis, then you will have to dig the appropriate pit, that is, it is very difficult to do without the involvement of special equipment.

• The use of a slab foundation automatically solves the problem of a reliable foundation for the floors of the first (or basement) floor.

This is a really important advantage. And if, simultaneously with the preparation of the slab for pouring, a high-quality thermal insulation belt is provided, then the floors will also be pre-insulated. In the "insulated Swedish stove", in addition, the contours of water heating of the floors are immediately mounted.

• Work on the slab foundation can in no way be attributed to tasks of an increased category of complexity.

An ambiguous statement, with which, nevertheless, one can agree to a certain extent. Indeed, the work on the stove itself does not involve operations that require the highest qualifications of workers. Digging a pit and tamping a sand and gravel pad, knitting a reinforcing cage, installing formwork, pouring and distributing concrete, caring for a slab that is gaining strength and other steps - all this is either initially clear, or a novice master can “fill his hand” in a very short time.

Another thing is that a number of operations require the involvement of special tools and equipment. So, for high-quality ramming, one cannot do without a vibrating plate, for quick and uniform manufacture of reinforcing clamps, it will be necessary to build an appropriate device, waterproofing with rolled materials involves the use of a gas burner with a cylinder. And considering that the volume of poured concrete can turn out to be considerable, and it is desirable to pour the slab in one day, it is hardly worth relying on - you will have to order it with delivery.

It can be said that, provided that forces and means are attracted from outside for some operations, the owner, with the help of friends or relatives, can easily cope with the main amount of work. True, one must be prepared for the fact that the work ahead is quite lengthy, physically difficult, and sometimes also tiring and monotonous. But for a small combined team of several strong men - doable. Of course, with strict adherence to all technological recommendations.

Interestingly, in some publications on foundation slabs, this is presented not as an advantage, but as a disadvantage - they say, working on such a slab is an extremely difficult task. Perhaps it's just a matter of various criteria assessment - from what point of view this problem should be considered.

Now let's turn our attention to flaws slab foundation:

• It is quite obvious that this type of house foundation is suitable for building on a relatively flat area. If a significant difference in height is observed in the building spot, then such a scheme either becomes extremely complicated, becomes impractical, or is recognized as completely impossible.

• The slab must completely, with its entire area, rest on the ground - this is precisely its increased bearing capacity even on not quite stable soils. And this, in turn, means that there can be no question of any basement or cellar under the stove itself.

The only exception can be the scheme already mentioned above, in which the slab itself becomes the floor of a full-fledged basement, semi-basement or basement. It, as a rule, has stiffening ribs-grillages directed upwards, or well-thought-out reinforcing tabs, from which further construction of the buried part of the walls is already underway, by analogy with a deep-laid strip foundation. But this type of foundation is a very expensive "pleasure" that requires highly qualified calculations and practical implementation.

• The construction of a slab foundation will require advance planning and laying the necessary engineering communications, for example, plumbing, and sometimes power cable.

It is unlikely that such requirements can be attributed to shortcomings - this is rather assessed only as a specific technological feature, and with well-planned work, it will not particularly complicate the entire construction process.

• There is a lot of talk about the high cost of such a foundation, which can reach almost half of the entire construction estimate.

Such frightening indicators, apparently, will be valid only for the deep-laid slab already mentioned above. If the foundation is practically not deepened, the picture is certainly not so “terrifying”.

Of course, even with a small plate thickness, but with a considerable total area, centimeters very quickly develop into cubic meters of concrete mortar. Two-tier reinforcement will require a significant consumption of reinforcement, of course, more than when pouring strip base. However, we must not forget that, along with the foundation slab, the developer immediately receives a ready-made foundation - in fact, the draft floor of the first floor, with it already completed with high quality, and sometimes with insulation. That is, these stages of work already fall out of the total estimate.

So the excessively high cost is by no means always an obvious drawback, and the ease of construction of the slab also largely compensates for the increased consumption of building materials.

How is a monolithic slab foundation calculated

Any foundation requires calculations, and the slab foundation is no exception in this matter. True, it should be specifically noted that the design of such structures is still the lot of professionals, especially if it is planned to build a full-fledged country mansion.

However, sometimes you can resort to calculations on your own, for example, during the construction non-residential buildings- a garage, a shed, a bathhouse, buildings for household purposes. And one of the key parameters of the calculation is always the thickness of the monolithic slab. Too small thickness may not be able to cope with bending loads, excessive thickening is an unnecessary expenditure of effort and money.

How is the optimal slab thickness calculated?

Ideally, the calculations should be preceded by an analysis of the soil on the building spot, since it is necessary to have an idea in advance about the bearing capacity of the formation on which the foundation slab will rest. Usually, specialists with a drilling rig are invited for this, who make several pits, for example, in the corners and in the center of the site.

This makes it possible to estimate the composition and thickness of the layers, the presence of a "perch water", the location of aquifers, on the basis of which further calculations can be carried out.

Any of the soils is characterized by its load resistance, that is, in fact, by its bearing capacity. This parameter can be expressed in kilopascals (kPa), but for calculations in the metric system it is more convenient to use the kilogram-force per square centimeter (kgf / cm²).

Soil type	Design soil resistance
	kPa	kgf/cm²
Coarse-clastic soils, gravel, crushed stone	500÷600	5.0÷6.0
The sands are coarse and gravelly	350÷450	3.5÷4.5
Sands of medium size	250÷350	2.5÷3.5
Dense sands of fine or silty fraction	200÷300	2.0÷3.0
The same sands, but of medium density	100÷200	1.0÷2.0
Sandy loam, hard and plastic	200÷300	2.0÷3.0
Loams, hard and plastic	100÷300	1.0÷3.0
Hard clays	300÷600	3.0÷6.0
Plastic clays	100÷300	1.0÷3.0

It is clear that the distributed pressure created by the mass of the planned house (taking into account also external loads on it) and the mass of the slab itself should not go beyond the specified limits. However, such a calculation will still not be objective enough.

When calculating the required thickness of the slab, it is better to operate with the values ​​of the optimal specific pressure on a particular soil - these indicators are determined specifically for slab foundations. The calculated value of the load from the entire structure, including the weight of the slab, should be as close as possible to the optimal ones, with a possible deviation not exceeding 20÷25%.

What is it for? It is important not to go to two extremes. If the optimal load value is exceeded, it is likely that the slab will begin to sink into the ground over time. However, a significant decrease in ground pressure is no less dangerous - a structure that is too light for specific conditions becomes too “floating”, that is, it can warp even with the slightest seasonal ground fluctuations.

Pay attention to the following:

• The second table does not show all types of soils. The fact is that on soils with a high bearing capacity, the very construction of a slab foundation simply does not make much sense - you can get by with much cheaper options.
• In addition, two rows are highlighted in the table. In both of these cases, it is recommended to conduct an in-depth analysis of the technical and economic feasibility of building a slab foundation.

- In the case of sandy loam, it is possible that the construction of a conventional strip foundation can be much more profitable.

- Hard clays are highlighted because the density of their structure is sometimes deceptive. If there is a possibility of waterlogging of these layers, for example, by closely located aquifers with seasonal fluctuations in their filling, then a sharp loss in the bearing capacity of the soil cannot be ruled out. The slab, together with the building, will gradually “sink”. It is worth considering the issue of greater, perhaps, the appropriateness of using

So, in order to calculate the required thickness of the slab, it will be necessary to determine what distributed load the building itself will exert on the base, then find the difference with the optimal pressure value, and cover the remaining "deficit" due to the mass of the reinforced concrete slab. Knowing the specific density of reinforced concrete, it is easy to calculate the volume, and having the area of ​​​​the slab as the initial data, it is possible to determine its optimal thickness. At the same time, do not forget to take into account the fact that the slab should protrude beyond the perimeter of all walls outwards by at least the value of its calculated thickness or even more - this already depends on the specifics of the project.

Below the reader will be offered a calculator in which this calculation algorithm is implemented. Undoubtedly, the accuracy of the calculations this application cannot compete with professional programs, but for an "estimate" in the field of hand-made construction, it can provide a useful service.

The calculator assumes that the developer has in his hands the design outlines of the future building, that is, it will not be difficult for him to determine the initial data. You will need to know the material and area of ​​\u200b\u200bthe walls (minus window and door openings), the area and type of ceilings, the area of ​​\u200b\u200bthe roof and the angle of steepness of its slopes (to take into account the snow load). The calculation program has already included the average values ​​of the specific gravity of materials of building structures, taking into account approximate operational loads (mass of decoration, furniture, large household units, dynamic loads from people living in the house, etc.).

How to correctly calculate the area of ​​\u200b\u200bstructures?

Since area values ​​\u200b\u200bare often used in calculations, it is worth giving appropriate recommendations on this matter. They are set out in a special article on our portal dedicated to, which, by the way, also has convenient calculators.

It is best to prepare the data necessary for the calculation in advance, write it out on a separate plate, and then proceed to the calculations.