How to determine the depth of a shallow strip foundation. Shallow strip foundation for a house with your own hands Where to make a shallow strip foundation

The beginning of the construction of any building is laying the foundation. When choosing the type of foundation, various factors should be taken into account, ranging from soil characteristics to the design features of the main structure. Recently, shallow strip foundations have become popular, due to its versatility, low construction costs and the ability to erect a structure without the use of heavy construction equipment.

When using a shallow foundation

Such a foundation can be safely erected for light suburban buildings of small number of floors. These can be houses made of wood and its varieties, from gas silicate and foam concrete blocks, frame-panel structures. It is possible to use a shallow foundation for brick houses, provided that the walls are of insignificant thickness.

The height of buildings erected on shallow foundations should not exceed three floors.

In addition, a shallow foundation is suitable for construction on soils prone to heaving, since a small depth protects the structure from the effects of heaving soil.

Features of the construction of a shallow foundation

When choosing a shallow foundation for a house, you should take into account some features of its construction:

• Such a base requires mandatory protection from precipitation. Therefore, it is very important to provide for the organization of a drainage system. This will move more water away from the foundation line. Our previous articles have detailed information about.
• One of the ways to protect a shallow foundation from precipitation and surface water is a blind area. Most professional builders insist on its arrangement. Find out more from our article:.
• When making such a foundation yourself, it is best to involve a large number of people in the work to ensure quick preparation of concrete and its one-time pouring.
• During the construction of a shallow foundation, only high-quality concrete should be used. Read a detailed article about.
• The main feature of this type of foundation is the need to complete the main construction before the onset of frost, since such a foundation cannot be left for the winter.

What should be taken into account when constructing an MZLF

A very important factor is the type of soil on the site. The fact is that on soils of organic origin and on clay, the construction of a shallow strip foundation is prohibited.

The groundwater level is no less important. Their very close location can cause rapid destruction of a shallow concrete strip.

Rules for calculating the load on a shallow strip foundation

When calculating the load on a shallow foundation, it is important to take into account all parameters. The total load on the foundation of the house can be constant or variable. In the first case we are talking about the following:

• Construction of the building and its features.
• The number of floors of the building and its total height.
• The material that is planned to be used for the construction of walls and partitions of the building.
• Load from the roof structure, including the weight of the roofing material.

In addition, seasonal loads from precipitation should be taken into account, especially in winter. It is in winter that the snow mass on the roof of the house exerts great pressure.

Variable loads include the number of residents, the weight of furniture and similar factors.

MZLF construction technology

The shallow concrete base strip is quite simple to construct, so all work can be done independently. In addition, this process will require several assistants, but you can do without heavy construction equipment.

Set of tools for work

The construction of a shallow shallow foundation requires a set of the simplest tools:

• Shovel, you can prepare a shovel and a bayonet shovel.
• Hammer and sledgehammer.
• Electric drill, grinder with discs, screwdriver.
• Roulette and building level.
• Regular rope or construction cord.

Trench

When determining the width of the trench, the width of the wall and the thickness of the formwork structure are taken into account. The foundation monolith itself should be flush with the wall, but taking into account the formwork, the width of the trench should be slightly larger. If construction is carried out on loose or heaving soil, then this trench parameter should be slightly increased.

Before you start digging a trench, you need to mark the area using wooden pegs and construction cord or rope. Pegs are driven into the corners of the future foundation, and the cord is pulled between them around the perimeter. In this case, both the internal and external perimeter should be noted.

If construction does not require precise calculations of a shallow concrete strip, then the depth of laying is determined by the location of the layer of hard clay. In this case, the bottom of the trench should be lowered 25-30 cm below the upper level of the clay layer.

For general information, it should be said that the soil most often has the following structure:

• The top 10 cm is a layer of fertile soil.
• The next 10-20 cm is occupied by a mixture of sand and clay.
• Below this layer is hard clay, which is quite difficult to dig.

The bottom of the trench should be deepened by about 30 cm in order to build a foundation and a cushion for it. Thus, the total depth of the shallow foundation is about 0.7 meters. This parameter fully meets the requirements for the construction of frame, panel and other light-weight buildings.

Making a pillow

In order for seasonal ground movements and other changes in the soil to be evenly distributed over the entire area of ​​the foundation base, it is necessary to create a kind of cushion of sand and crushed stone. The sand layer should be about 5 cm thick. The sand is poured into the trench, leveled, watered and thoroughly compacted. Crushed stone is poured in a layer of the same height, leveled well, compacted and filled with liquid cement mortar. As a result of the actions performed, the base of the foundation is obtained.

Reinforcement

The strength and reliability of any foundation is ensured by a frame made of reinforcing bars. It is not recommended to neglect the creation of a reinforcing belt, since it takes on the main load. For the same reason, you should not skimp on fittings or use low-quality elements.

To create a reinforcing belt, you need to take reinforcement bars with a cross-section of 10-12 mm and tie them together, creating two levels of two bars each. The width and height of the reinforcing frame are determined by the parameters of the foundation; the reinforcement must retreat from each edge of the foundation by 5 cm. The main rods of the frame must be connected to each other with vertical and transverse rods. For knitting it is best to use a special soft wire. If it is necessary to connect rods along the length, it is important to overlap the ends of the reinforcement by 10-15 cm.

Formwork structure

The formwork can be erected before assembling the reinforcing belt, but for convenience this stage is postponed a little. The fact is that in a finished formwork structure it is much more difficult to knit the frame.

The main purpose of the formwork is to form smooth walls of a concrete strip, so for its manufacture it is necessary to use panels made of boards or plywood. The inside of the boards should be as smooth as possible, so the boards are well processed (find out). In order for the structure to hold the heavy concrete mass inside, it is recommended to make supports and lintels. Supports are installed on the outside of the structure at a distance of 50-60 cm, lintels are secured along the upper edge of the panels so that the formwork does not move apart under the pressure of concrete.

Pouring concrete

A high-quality foundation can only be achieved by using high-quality concrete. Therefore, a factory-prepared solution is considered the ideal option. Most experienced craftsmen advise using this option whenever possible. However, with a small construction budget, savings are required at every stage, including the preparation of concrete. A mobile concrete mixer can be an excellent solution to the problem; it can be rented, which will significantly save money.

The quality of concrete also depends on the components used and their quantity, therefore, maintaining proportions and quality ingredients will help to make a strong and reliable foundation for a house or other building.

It is recommended to pour concrete in one step, and the thickness of one layer should not exceed 20-25 cm. After pouring one portion, it is necessary to compact the concrete mass; for this purpose, use a vibrator or an ordinary metal rod. In the latter case, the concrete is carefully pierced in several places, removing air bubbles. Compaction of the concrete solution helps to increase the strength of the entire base.

Insulation and waterproofing

To avoid freezing of a shallow foundation, do not neglect the insulation and waterproofing of the base. In this case, the protection must cover both vertical and horizontal walls.

You can make a shallow strip foundation with your own hands. In this case, it is necessary to take into account the main factors that influence the quality of the foundation, take into account the features of constructing a foundation of this type and follow the technology of its construction.

When constructing a building, it is important to wisely select the types of main load-bearing structures. This will reduce the labor intensity of the work, financial costs and construction time of the facility. One of the types of construction that makes it possible to simplify the process of building a building is a shallow strip foundation. When constructing it, you need to take into account a large number of nuances, but if you follow the technology and choose wisely, you can save a lot.

Application area

This type of tape has a fairly limited area of ​​use. Do not bury foundations deep if:

Construction of a shallow foundation at a high groundwater level

• it is planned to construct a building from light materials (wood, aerated concrete);
• the site has a high level of groundwater;
• The characteristics of the foundation soil are quite good, the soil has high strength characteristics.

When building a frame house or a house made of aerated concrete, installing a shallow strip foundation is the best option. It will reduce the volume of excavation work and increase the speed of construction. It is possible to make such a structure without taking additional measures to remove water from the site if the groundwater is located at a distance of 1 meter or more from the surface of the earth. For a recessed belt, this value is much higher (50 cm more than the laying of the sole).

A shallow strip foundation is suitable for conditionally non-heaving soils and non-heaving soils, which include:

• rocks;
• coarse-clastic foundations (including those with dusty filling);
• coarse and medium gravelly sands;
• clay soils of hard consistency with natural moisture.

You can determine the composition of the soil on the site yourself by digging holes or by hand drilling. GOST “Soils. Classification".

Foundation types

Shallow foundation has two classifications. The first depends on the manufacturing method:

• monolithic;
• made.

It is better to make a shallow strip foundation using monolithic technology, since in this case you will not have to worry about ensuring the joint operation of the strip. When building a prefabricated structure for a house made of aerated concrete, it will be necessary to additionally provide a monolithic belt along the edges, so monolithic work cannot be avoided in any case.

Depending on the type of section, there are:

• rectangular;
• T-shaped.

Rectangular foundations have a lower load-bearing capacity, which is why they are more often used for the construction of frame houses. To build a house from heavier aerated concrete, it would be correct to choose a T-shaped section.

This type differs from the rectangular one by the presence of a widened base, which can significantly increase its load-bearing capacity even at a shallow depth. The shallow foundation in this case consists of a strip located horizontally (pillow) and a vertical part.

Foundation depth

In order to correctly design a support for a building, it is necessary to select the depth of the foundation. For this type of tape, almost throughout the entire country it will be higher than the soil freezing depth, which increases the risk of damage to the structure by frost heaving forces.

Frost heaving is a phenomenon when water in the soil freezes and increases in volume. In this case, the foundation strip is deformed and subjected to additional loads. Cracks are starting to appear in the structure. That is why it was said above that a shallow foundation is mainly used for non-heaving soils.

The laying depth is determined depending on freezing, which is calculated according to SN “Foundations and Foundations” or found from tables. Minimum depth:

• when freezing to a depth of less than 2m - 50cm;
• when freezing less than 3m – 75cm;
• when freezing more than 3 m - 100 cm.

It is also important to consider the location of groundwater. If the water is located closer than 2 meters from the expected level of the base, and the soils on the site are clayey, loamy, sandy loam, fine or silty sand, it would be correct to choose a buried foundation with a drainage system.

Regulatory documents also require that the foundation depth for a house made of aerated concrete be chosen to be at least ½ of the freezing depth for clays and loams with deep water.

This is caused by the increased heaving of this type of soil.

Protection methods

Before you build a shallow strip foundation with your own hands, you need to familiarize yourself with the technology of protecting it from negative external influences. Frost heaving is caused by two factors:

• high humidity;
• low temperatures.

To avoid this phenomenon, take measures to protect against these negative influences:

1. Insulation of aerated concrete house strip along the entire height of the building. Made using extruded polystyrene foam. Using this particular material correctly; using polystyrene foam or mineral wool is highly not recommended.
2. Additional insulation of the foundation thanks to the warm blind area of ​​the house. It can be made from concrete or asphalt concrete by placing a heat-insulating layer under the material. Extruded polystyrene foam or expanded clay gravel is used as insulation. The thickness of polystyrene for most regions will be 100-150 mm, the thickness of the expanded clay layer is assumed to be around 30-50 cm.
3. Vertical waterproofing. The layer is provided under the insulation. Made from bitumen roll materials or mastic.
4. Drainage of water from the foundation. This will require a storm drain (from rainwater) and drainage (from underground moisture). Drainage pipes are laid 30-50 cm below the base of the tape and at a distance of no more than 1 m.
5. Sand preparation device 30-50 cm thick. Coarse or medium sand is a non-heaving material. Replacing part of the soil with it allows you to increase the reliability of the foundation.

Carrying out all these measures will reduce the likelihood of damage to the structure of an aerated concrete house due to frost heaving in the winter.

Manufacturing technology

It is not much different from performing work on a buried belt. The installation of a shallow strip foundation is carried out in the following order:

1. The terrain is marked and a trench or pit of the required dimensions is dug.
2. Sand preparation is being arranged(it was mentioned earlier). When laying, it is necessary to ensure layer-by-layer compaction of the layer (by vibration, pouring or weights).
3. The formwork is being installed. For the type of foundation under consideration, the most optimal option is foam. After pouring, no additional insulation work will be required. Can be used as formwork boards.
4. Reinforcement of the structure. For private houses, reinforcement can be performed without preliminary calculations. Reinforcement in a structure is of three types: working longitudinal, structural horizontal, structural vertical. Structural reinforcement plays the role of a connecting link between the working rods. The minimum diameter of the rods is 8 mm. Working reinforcement with a diameter of 12-16mm is laid in two rows: upper and lower. The total cross-section of the working rods of a house made of aerated concrete or wood should be equal to approximately 0.1% of the cross-section of the foundation.
5. Pouring concrete mixture. Performed in one step. If absolutely necessary, you can do it in layers, but this is not advisable. For foundation work, concrete B15-B25 is used, depending on the load.
6. Vibrating concrete for compaction.
7. Strengthening concrete and maintaining it.
8. Removal of formwork (if necessary).
9. Foundation waterproofing.
10. Insulation (if necessary).
11. Backfilling.
12. Blind area device.

To make a reliable foundation, you need to carefully consider each stage of the work: correctly select the laying depth, reinforcement, grade of concrete, and carry out all the necessary protection measures.

The foundation is the main component of any structure, as it acts as its supporting structure, on which the durability and safety of operation depends. Recently, for the construction of frame houses, summer cottages and commercial facilities, they have chosen to install a shallow strip foundation.

It is ideal for all types of soil, is characterized by high strength, and laying it can be easily done with your own hands.

Peculiarities

A shallow strip foundation is one of the modern types of foundations that are used in the construction of both one-story and two-story buildings made of foam blocks, expanded clay and wood. According to the requirements of SNiP, such foundations are not recommended for buildings with a height of more than 2 floors that exceed an area of ​​100 m2.

Such structures are considered a good option for buildings on clay, but during their design the size of the structure must be taken into account.

GOST also allows shallow strip foundations for unstable soil. Thanks to their design features, they can move along with the soil, protecting the building from possible shrinkage and destruction; in this, they are inferior to a columnar foundation.

To make the foundation reliable and durable, it is installed on bored piles and monolithic reinforced concrete slabs are laid, which are deepened into the soil by 40-60 cm. First, the area is carefully leveled, then formwork is laid around the entire perimeter, the bottom is covered with sand and reinforcement is laid. For such a foundation, as a rule, a monolithic slab with a thickness of 15 to 35 cm is made, its dimensions depend on the dimensions of the future structure.

• In addition, a shallow strip foundation has some features that must be taken into account during its construction:
• on heaving soil, it is imperative to create monolithic reinforced concrete structures that will help reduce the load from above and balance the heaving forces from below;
• laying should be done on well-prepared and pre-compacted soil;
• if the groundwater level is high, it is necessary to provide for the laying of high-quality waterproofing and installation of a drainage system;
• a shallow foundation requires insulation from above, since a layer of thermal insulation will protect the base from temperature changes and serve as an excellent source of heat.

Advantages and disadvantages

Today, when constructing buildings, you can choose any type of foundation, but the shallow strip foundation is especially popular among developers, as it is considered the most reliable and has positive reviews when operating structures on heaving soils and clay. It is also often installed on a site with a slope, where a recessed version of the structure cannot be implemented. The main advantages of such a foundation are considered to be several characteristics.

• Simplicity of the device. Even with minimal skills, it is quite possible to lay the structure with your own hands without the use of lifting mechanisms and special equipment. Its construction usually takes several days.

• Durability. By observing all technologies and construction standards, the foundation will last more than 100 years. In this case, special attention should be paid to the choice of concrete grade and reinforcement.
• Possibility to design houses with a ground floor and a basement. With this layout, the reinforced concrete strip will serve as both a load-bearing structure and walls for the basement.
• Minimum costs for building materials. For the work you will only need reinforcement, concrete and ready-made wooden panels for making formwork.

As for the disadvantages, these include some features.

• Labor intensity. For construction, it is necessary to first carry out excavation work, then make a reinforced mesh and fill everything with concrete. Therefore, to speed up the installation process, it is advisable to use the help of specialists, but this will entail additional costs.

• Easy to build. In the case when laying is carried out in winter, concrete acquires its strength later, after 28 days. This means that you will have to wait a month, since the base cannot be loaded.
• Lack of ability to construct tall and large buildings. Such a foundation is not suitable for houses whose construction is planned from heavy material.
• Need for additional styling waterproofing.

Calculation

Before laying the foundation, it is necessary to carry out design and make accurate calculations. The difficulty of carrying out calculations for a shallow strip foundation lies in determining the hydrogeological characteristics of the soil on the site. Such studies are mandatory, since not only the depth of the foundation will depend on them, but also the height and width of the slabs will be determined.

In addition, in order to make correct calculations, you need to know the basic indicators.

• The material from which the building is planned to be constructed. A strip foundation is suitable both for a house made of aerated concrete and for buildings made of foam blocks or timber, but will differ in its structure. This is due to the different weight of the structure and its load on the base.
• Dimensions and area of ​​the sole. The future base must fully correspond to the dimensions of the waterproofing material.
• The area of ​​the outer and lateral surface.
• Diameter dimensions of longitudinal reinforcement.
• Brand and volume of concrete solution. The mass of concrete will depend on the average density of the solution.

In order to calculate the laying depth, you must first determine the bearing capacity of the soil at the construction site and the parameters of the base of the tape, which can be monolithic or consist of blocks. Then you should calculate the total load on the foundation, taking into account the weight of the ceilings, door structures and finishing materials.

It is also important to examine the depth of soil freezing. If it is from 1 to 1.5 m, then the laying is carried out at a depth of at least 0.75 m; if it freezes to more than 2.5 m, the base is buried to a depth exceeding 1 m.

Materials

Installing a foundation for a building involves the use of high-quality building materials; a shallow strip foundation is no exception. It is erected from a reinforced concrete frame on a sand cushion, and the layout can be either monolithic or consist of blocks.

To reinforce the base, steel rods are used, which, depending on their characteristics, are divided into classes A-I, A-II, A-III. In addition to rods, reinforcement cages, rods and meshes are also laid into the thickness of the concrete. The mesh and frame is a structure made of transverse and longitudinal rods that are attached to each other.

The reinforcement scheme is chosen in accordance with the design features, and it depends on the loads on the foundation. Steel rods with a diameter of 10 to 16 mm are well suited for installing a shallow foundation; they can withstand loads and stretch well. Transverse reinforcement is usually performed using smooth wire with a diameter of 4-5 mm.

Knitting wire is also used as an auxiliary material; it is used to fix the rods in the manufacture of the mesh and frame.

To increase the service life of the foundation, all reinforcement elements must be protected from external factors; for this, a gap of 30 mm is left between the edges of the rods and the concrete.

In addition to the protective layer, the reinforcement is additionally placed on supports, so for construction, both special supports sold in stores, and pieces of steel or scraps of metal can be useful. During the laying of the foundation, the production of formwork is provided; it can be purchased either ready-made or knocked down yourself from wooden boards.

To backfill the air cushion, medium-sized sand is used, and the filling is performed with concrete mortar of different grades. In this case, concreting is best done with a high-class solution, grade M100 and higher.

Device stages

The technology for installing a shallow foundation is not particularly difficult, so it is quite possible to do all the work yourself. Before you start laying the foundation, you need to draw up a project, as well as an action plan, in which all the activities “from A to Z” should be spelled out. In order for the foundation to reliably serve for decades, it is important to pay attention to such points as insulation, waterproofing and frequency of reinforcement fastening.

It is best if the foundation is monolithic.

It is also important to first make a geodetic assessment of the soil, which will determine the groundwater level, soil composition and freezing depth. The choice of foundation type and the depth of its laying will depend on these parameters. In the event that a budget construction option is planned, then it is enough to simply drill several holes in different places on the site and study the soil yourself.

Soil that contains an admixture of clay will easily roll into a ball, but if it cracks during formation, then the soil consists of loam. Sandy soil cannot be rolled into a ball, as it will crumble in your hands.

Once the composition of the soil has been determined, construction of the foundation can begin. As a rule, step-by-step instructions involve performing the following steps:

• calculation of the cross-section of reinforcement, width of the tape and drawing up a reinforcement diagram;
• making a pit for the basement or a trench for buildings without a basement;
• laying drainage system and thermal insulation;
• installation of formwork and fastening of reinforcement;
• pouring concrete and installing waterproofing after stripping.

The completion of laying the foundation is considered to be the insulation of the blind area; for this, it is lined with a special material that is resistant to moisture. If all points of the instructions are carried out correctly, in compliance with technologies and construction standards, then the resulting shallow strip foundation will not only become a reliable basis for the structure, but will also serve for a long time, protecting the structure from external influences.

Excavation

The construction of the foundation should begin with preliminary preparation of the land plot; it is thoroughly cleared of debris, plants and trees, and the fertile layer of soil is removed. Then markings are made and all measurements specified in the building design are transferred to the work site. To do this, use pegs and rope. First of all, the facade walls of the building are marked, then two other walls are placed perpendicular to them.

At this stage, it is important to control the evenness of the diagonals; at the end of the marking, a rectangle is obtained that compares all the diagonals.

Beacons are hammered into the corners of the future structure, keeping a distance of 1 m between them. The next step is to install a wooden blind area on which the ropes will be stretched. Some craftsmen simply mark the dimensions of the foundation on the ground using lime mortar. Then a trench is dug; its depth should correspond to the thickness of the sand cushion and tape.

Since usually the thickness of the sand cushion does not exceed 20 cm, a trench 0.6-0.8 m wide and 0.5 m deep is made for a shallow foundation.

If the project involves the construction of heavy structures with stairs, a porch and a stove, then it is recommended to dig a pit. To make a pillow with a thickness of 30 to 50 cm, crushed stone and sand are used; the most common option is a pillow consisting of two layers: 20 cm of sand and 20 cm of crushed stone. For dusty soil, it is necessary to additionally place geotextiles in the trench.

The pillow is filled in layers: first of all, a layer of sand is evenly distributed, compacted well, moistened with water, then gravel is poured and compacted. The pillow should be placed strictly horizontally and covered with waterproofing in the form of roofing material on top.

Formwork

An equally important point when laying the foundation is the assembly of the formwork. To make it, panel materials such as OSB sheets, plywood or boards with a thickness of at least 5 cm are used. In this case, the boards should be knocked down into panels. The formwork must be calculated in such a way that it is several centimeters higher than the future concrete level. As for the height of the tape, it is made equal to or less than the depth of the foundation; as a rule, it is 4 times the width of the tape.

The prepared shields are fastened together using nails or self-tapping screws, after which they are additionally supported with pegs. It is worth paying attention to ensure that all fasteners do not stick out and extend into the formwork. If you ignore this, then after pouring they will end up in the concrete and can cause cracks or chips.

The formwork of a shallow strip foundation is also additionally reinforced with struts made from timber with a cross-section of 5 cm; such supports are placed externally at a distance of 0.5 m.

In addition, in the formwork you need to prepare holes for communications in advance and insert pipes. The inside of the structure is covered with polyethylene, it will enhance waterproofing and reduce adhesion to concrete.

It is also possible to use permanent formwork made from extruded polystyrene foam.

Reinforcement

The construction of this type of foundation includes mandatory reinforcement. The reinforcement can be either knitted with wire or welded, but the latter option is not recommended for connecting metal rods, since over time corrosion will appear at the fastening points. To install the frame, a minimum number of rods is required, at least 4 pieces.

As longitudinal reinforcement, it is necessary to use material with a ribbed section of class AII or AIII. Moreover, the longer the rods are, the better the frame will be, since the connections reduce the strength of the structure.

The transverse parts of the frame are assembled from smooth and thinner reinforcement with a diameter of 6 to 8 mm. To install a shallow foundation, two reinforcing belts consisting of only 4 longitudinal rods will be sufficient. It is important that the edges of the reinforcement extend 5 cm from the foundation, and the step between vertical fastenings is at least 30-40 cm.

The crucial point in the work is the manufacture of the corners of the frame: the rods must be bent in such a way that the approach to the other wall is at least 40 mm from the diameter of the rods. In this case, the distance between the corners formed by the vertical jumpers should be half the distance in the wall.

Fill

The completion of the foundation installation work is pouring concrete. Experts recommend using factory-made concrete of a grade no lower than M250 for this purpose. If you make the solution yourself, you should first prepare a concrete mixer, since it will be difficult to do this manually. The base must be filled with solution immediately; to do this, it is evenly distributed over the entire surface and compacted. Each layer of fill should be carefully aligned with the mark marked on the formwork.

Experienced craftsmen who have made hundreds of foundations advise sprinkling the concrete with dry cement after pouring, this will improve its quality and the top layer will set faster.

As a rule, one month is allowed for the base to completely harden, after which construction work can continue.

Basic mistakes

Since the foundation is the main component of any structure, its laying must be done correctly, especially for a shallow strip foundation, which is installed on loose soils and clayey soils. Any mistake made during its construction can nullify all construction work. When making a foundation on their own, inexperienced craftsmen make several common mistakes.

• Construction begins without calculating the main dimensions and load on the foundation.

• The base is poured directly into the ground, without sprinkling and making a sand cushion. As a result of this, in the winter season the soil will freeze to the concrete, dragging and lifting the tape upward, as a result of which the foundation will begin to swell under the influence of frost, and the floor of the basement will crack. This is especially true in cases where there is no insulation.

• Choose the number of rods and the diameter of the reinforcement at your discretion. This is unacceptable, since the reinforcement of the foundation will be incorrect.
• Construction is carried out over more than one season. The entire cycle of work should be distributed so that laying the foundation, laying out the walls and insulating the blind area is completed before the onset of cold weather.

In addition, protecting the concrete base with film is considered a big mistake. Don't close it. The poured solution must have access to ventilation.

To learn how to make a shallow strip foundation with your own hands, see the following video.

Looking at the design of a new house, the owner estimates how many cubes of concrete and tons of reinforcement will have to be laid in the foundation. Without this, there is no guarantee that the structure will not crack or tilt under the powerful pressure of frozen soil.

The “dig deeper” principle will not let you down. It has been tested for centuries. However, there is a more economical way of construction. It is called a shallow foundation and can be used for the construction of wooden log houses and one-story frame-type buildings.

It is obvious that a shallow foundation saves a lot of money and time. Unfortunately, it may not be applicable everywhere and not always. As we have already said, this is a good option for low-rise buildings.

It is possible to lay a shallow strip base only if there is no heaving soil underneath. Otherwise, the uneven rise of frozen soil or its subsidence in a waterlogged state will cause critical deformations of the concrete foundation of the house.

In its design, a shallow strip foundation is no different from a traditional one. The main difference is the laying depth, which in this case does not exceed 50-60 cm. What is the main technological “highlight” of such a design, which allows it to withstand seasonal ground fluctuations?

The answer is very simple. When constructing a shallow strip foundation, a thick layer of sand is laid under the concrete. It serves as a kind of buffer between natural soil and reinforced concrete. Small vibrations in the soil are absorbed by the sand cushion.

Water, once in the sand, quickly goes into the underlying layers. Even if it freezes, nothing bad will happen. The sand cushion will rise evenly under the foundation, and after the ice melts it will fall again. There will be no damage to the building from such changes.

As you know, a conventional strip foundation is laid deep (1.7-2.5 meters) not at all due to the insufficient strength of reinforced concrete. This depth is needed so that the sole is below the freezing mark of the soil. In this case, the forces of frost heaving do not put pressure on the sole from below and the house stands securely.

With this in mind, we do not advise anyone to joke with heaving soils. Build a shallow foundation only in areas where groundwater is low and the soil does not have a large amount of clay, silty sand, peat or loess-like loam in its structure.

The benefit of such a solution is obvious, since the estimate for the construction of a shallow foundation is 2-3 times less than the standard one. The labor intensity and construction time will decrease accordingly.

Construction technology

A shallow strip foundation is built with your own hands in several stages. Let's look at each of them in detail.

1. Having marked the contour of the foundation on the site along the cord, you need to dig a trench. Its width should be 20-30 cm greater than the width of the foundation. This is necessary for laying a wide sand cushion that compensates for seasonal fluctuations in the soil.

2. A sand cushion 30-40 cm thick is poured out. Pay special attention to the density of the sand. To do this, it must be moistened layer by layer with water and compacted thoroughly.

3. Prepare panels from OSB boards or edged boards, they are placed in a trench and reinforced with wedges and spacers made of wooden blocks. The spacing of the wedges and spacers must be at least 60 cm so that the wet concrete does not burst apart the formwork frame.

If you make boards from boards, be sure to line them on the inside with glassine, which will prevent the laitance from escaping from the concrete into the ground. As you install the formwork, you need to check its horizontalness and verticality. When knocking down panels with nails, be sure to bend the protruding ends. This will make further disassembly of the formwork easier.

4. Reinforcement of the foundation is carried out with reinforcement with a diameter of 12 to 18 mm. It is laid along the “ribbon” in two to four rows. Two reinforcing belts are installed: lower and upper. They are connected into a single spatial structure with thick wire or welding.

Don't forget to leave a gap between the bottom chord of the reinforcement and the base of the foundation. It should be within 40-50 mm. To do this, place scraps of plastic pipe under the rods. The upper belt should also not reach the concrete pouring level by 3-5 cm, so that the metal does not corrode.

Before installing the formwork, you need to decide whether the shallow foundation will be insulated. If yes, then use this wisely and instead of covering the formwork with glassine, attach sheets of foam plastic 4-5 cm thick to it. They will insulate the structure and cut off the path for the solution to “escape” from the formwork.

5. Concreting also has its own subtleties. Concrete should not be laid haphazardly, but in a continuous horizontal layer. If you fill it in short and high sections, vertical seams will form, which will weaken the structure. Careful compaction of concrete by vibration or bayonet has also not been canceled (every 20 cm of layer).

Do not rush to remove the formwork, even if it seems to you that the concrete is hard enough. At least 5-6 days must pass before it is disassembled.

6. After removing the formwork, coat the top and sides of the concrete or cover them with roofing felt. The gaps in the trench need to be filled with sand, compacted, then a layer of roofing material should be laid on top and a concrete blind area made over it (width 80-100 cm, thickness 10-12 cm).

If all the steps are completed carefully and correctly, then all you have to do is calculate the money saved and calmly begin building the walls.

For the construction of small houses, as well as various outbuildings, the best foundation option is a shallow foundation. Its construction will not take much time, and the entire process can be completed independently. In order for a shallow strip foundation to be as strong as possible with your own hands, you need to correctly calculate its parameters and strictly follow the pouring technology.

The depth of a conventional foundation is at least 1.5 m, and in cold regions - up to 2 m. A shallow foundation is located at a depth of up to 70 cm, which greatly facilitates trenching and reduces construction time. Since the area of ​​such a foundation is several times smaller, the consumption of building materials is also reduced. Not only concrete, but also red brick and concrete blocks are suitable for its manufacture.

The shallow foundation also has its disadvantages: it is only suitable for the construction of one-story buildings of a small area; requires the arrangement of a drainage system on heaving soils. Such a foundation can be poured only in the warm season, and it cannot be left unloaded for the winter. When the soil freezes, it pushes out the lightweight foundation, damaging its integrity.

Foundation construction technology

The fastest option for a strip foundation is a monolithic concrete foundation. It is built from blocks or bricks if it is not possible to prepare a large amount of mortar and pour the base at one time. To ensure that the construction process is not interrupted, you should prepare all the necessary tools and materials in advance.

So, to work you will need:

• roulette;
• plumb line or level;
• wooden pegs or iron rods;
• thick fishing line;
• pick-up and bayonet shovel;
• geotextiles;
• sand;
• crushed stone;
• reinforcement with a cross section of 12 or 16 mm;
• formwork materials;
• polyethylene;
• concrete solution;
• trowel.

The area for a shallow foundation should be relatively flat, with dense, homogeneous soil. The location of the house relative to the site is determined and a peg is driven in at the site of one of the corners of the facade. Measure the distance to the second corner and again place the beacon from the peg. A fishing line is pulled between the pegs, secured, then perpendicular lines are drawn from each corner. Having connected the beacons into a rectangle, they check the perimeter along the diagonals. If the angles and sides of the marking are equal, you can mark the internal perimeter according to the project.

The width of the foundation strip is usually 40 cm, so inside the markings it is necessary to mark the internal boundaries of the base. To do this, step back 40 cm in both directions from each outer corner along the stretched fishing line. These points are marked with beacons, and then they retreat from them beyond the perimeter by 20-30 cm and drive in pegs. This is necessary for more accurate designation of angles, both external and internal. In addition, while digging, closely spaced pegs can accidentally get caught and knock down the markings.

The soil is removed to a depth of 70 cm, counting is carried out from the lowest marking point. The walls of the trenches must be strictly vertical, which is periodically checked with a building level. If the soil is crumbling, wooden supports should be installed as you move along the perimeter. When the trenches are ready, check the horizontal level of the bottom and correct defects.

To avoid shrinkage and deformation of the strip foundation, a sand cushion is required. It is recommended to use coarse-grained river sand, which better resists compression. To protect the sand cushion from erosion, the bottom and walls of the trenches are covered with geotextiles. You can also use regular polyethylene, the main thing is that the sand does not mix with the soil. The material is spread inside the trenches, and its edges are brought up and secured with something, for example, with bricks. This will not allow the geotextile to move while compacting sand and laying reinforcement.

In an area with clay soil, the thickness of the cushion should be at least 50 cm, but if the soil is predominantly sandy, 20 cm is enough. The sand is poured in 2-3 steps, tamping it thoroughly each time. For better compaction, layers of sand are shed with water. A layer of gravel about 10 cm thick is poured on top of the sand cushion, and it is also compacted well. After this, the formwork can be installed.

Shallow strip foundation - trench

Assembly and installation of wooden formwork

Smooth boards with a thickness of 2 cm or more, durable plywood, and OSB boards are suitable for formwork. The sheet material is cut into pieces with a width of 40 cm, and the boards are knocked down into panels. It is more convenient to connect the formwork elements with self-tapping screws, then dismantling the structure is much easier. When assembling the panels, it should be taken into account that the inner side should be as smooth as possible, otherwise all irregularities will appear on the foundation walls. Since wood strongly absorbs water from the solution, the formwork should be covered with plastic film.

When the required number of panels is ready, they begin to install the formwork. Parts of the formwork are placed on both sides of the trenches, leveled horizontally and vertically, and knocked down along the upper edge with transverse bars at certain intervals. Next, the structure is strengthened with spacers from the outside so that the formwork walls do not come apart when pouring. At the end of the installation, you should make sure that there are no gaps or cracks in the formwork, and that the walls are positioned strictly vertically.

On the inner walls of the shields, mark the level of filling the solution; They do this along the entire perimeter of the trenches so that the surface of the shallow foundation lies in the same horizontal plane. Instead of markings on the walls, many builders use fishing line: they stretch it inside the formwork and secure the ends with nails. This must be done after installing the reinforcing frame.

Frame installation

The reinforcing frame is knitted from reinforcement with a diameter of 12 cm. Rods are cut from the reinforcement to fit the width and length of the trenches, and then tied into a lattice. The dimensions of a standard cell are 30x30 cm. Soft wire is used for binding, but it is not advisable to weld the frame: welding reduces the tensile strength of the metal, which leads to cracks in the base. In addition, welded grating is more susceptible to corrosion.

Having laid the lattice on the bottom, they tie the frame with reinforcement at the joints. If the height of the base exceeds 30 cm, the reinforcing frame should be made two-level. To do this, knit a second layer of gratings, and then connect them to the bottom layer with vertical rods. The reinforcement should not touch the walls of the trenches and formwork, or reach the concrete pouring level. Metal protruding from the foundation will quickly rust from rain and snow, which means the strength of the foundation will be reduced.

The strength of a shallow foundation directly depends on the quality of the concrete. For filling, it is recommended to use a solution of grade M200 and higher. When making the solution yourself, pour 1 part of cement into a container, add 3 parts of sifted sand and 4-5 parts of fine gravel or crushed stone. If everything is done manually, first mix the dry ingredients, and then gradually add water.

Although the height of the foundation is small, it is recommended to fill the trenches in layers. This will help compact the solution better and distribute it more evenly. The first layer is poured 20 cm thick, leveled if possible and pierced to the bottom with a piece of reinforcement in several places. Particular care should be taken to pierce the corners. The second layer is poured immediately after the first, without waiting for the concrete to set. Again, distribute the solution in the corners, under the frame rods, at the joints of the walls, and get rid of air voids.

The last layer of concrete is leveled along the line, the surface is smoothed with a trowel, and then sprinkled with dry cement through a sieve. This contributes to faster setting and strengthening of the solution; in addition, the surface sprinkled with cement does not crack when drying. The finished foundation should be covered with a film from scorching rays and from rain for 28 days, until the concrete is completely dry.

To extend the service life of a shallow foundation, it is recommended to insulate its outer walls with polystyrene foam boards or polyurethane foam. It is advisable to make a blind area 1 m wide along the perimeter of the base, and additionally install drainage ditches in flooded areas.

Shallow foundation made of bricks or blocks

The construction of such a foundation has slight differences. Used bricks can be used, as long as they are fired and intact. You can make the foundation blocks yourself, which will allow you to save a little on materials.

So, the construction of the foundation is carried out as follows:

• mark the area and dig trenches;
• lay geotextiles, a sand cushion and a layer of crushed stone;
• knit and lay out reinforcement, the top of which should not reach approximately 5 cm to the edge of the trench;
• fill the holes with concrete flush with the ground, level the surface;
• after the concrete layer has set and hardened, several rows of blocks or bricks are laid out with mandatory bandaging of the seams;
• The outer walls of the foundation are insulated and covered with cement plaster on top.

If the foundation is intended for utility rooms, it does not need to be insulated, but the masonry can be immediately plastered with mortar. If the described technology is followed, the foundation will last for several decades.

Video - Do-it-yourself shallow strip foundation