Shallow strip foundations have become popular for the construction of private houses due to their versatility and the ability to install them without the use of heavy equipment and for relatively little money. How to properly build a shallow strip foundation with your own hands?

When is MZLF used?

A shallow strip foundation (MSLF) is a type of strip foundation with a laying depth of no more than 70 cm. This type of foundation has become widespread in individual construction due to several significant advantages:

• relatively low cost,
• small volume of earthworks,
• no need to use heavy equipment,
• applicability on different types of soil,
• low cost of building materials.

It is possible to build houses of up to 3 floors from timber, logs, frame, brick with lightweight masonry, and foam concrete.

A shallow foundation is suitable for both non-heaving and heaving soil. It cannot be done on biogenic soils: peat, sapropel, or clay.

Types of MZLF

A shallow strip foundation can be either monolithic or prefabricated. A monolithic foundation is a reinforced concrete strip, which is located around the perimeter of the building and under the load-bearing walls. In the case of a precast foundation, this strip is made from foundation blocks held together with cement mortar. It will take much less time to create a prefabricated foundation, but its service life is shorter than that of a monolithic one.

A combination of pile and strip foundation - a shallow pile-strip foundation. In this case, the tape rests on screw or bored piles, and a sand or crushed stone cushion is made under it. Pile foundations are made on difficult soils or when there are differences in elevation on the site.

Construction procedure

Before making a shallow strip foundation, it is necessary to conduct a geodetic examination to find out

• soil composition and quality,
• the depth of its freezing,
• ground water level.

These parameters influence the choice of foundation type and its depth. However, if you want to save on expensive expertise, to assess the quality of the soil, it is enough to drill holes in several places on the site.

• Clay soil can be rolled into a ball by hand.
• Loam can also be rolled into a ball, but it will have cracks.
• The sandy loam soil will partially crumble.
• It is impossible to roll sandy soil into a ball.

The construction site must be cleared of debris and plants, trees must be uprooted, and the fertile layer of soil must be removed.

Next, markings are made - the dimensions of the house are transferred to the site. To do this you will need rope and pegs. First of all, note the front wall of the house, which faces the street. Next, two other walls are built perpendicular to it. To check whether the rectangle is even, compare its diagonals. There are beacons in the corners. At a distance of about a meter from this contour, a blind area of ​​boards is installed, onto which ropes are pulled, showing the dimensions of the strip foundation. You can mark the dimensions directly on the ground with lime mortar.

After this, they dig a trench. Its depth is equal to the thickness of the tape plus the thickness of the sand cushion. The thickness of the cushion is usually 20 cm. Typically, a trench for a shallow strip foundation is made 0.5 m deep and 0.6-0.8 m wide.

Under heavy structures, such as a stove, porch, stairs, pits are dug.

The pillow is made of sand, crushed stone or a mixture of them, 30-50 cm thick. A common option is also a two-layer pillow: 20 cm of crushed stone and 20 cm of sand. If the soil in the area is dusty, then before filling the cushion, you need to lay geotextiles in the trench.

The pillow is poured in layers, compacting each layer. If it is two-layer, first pour 10-15 cm of sand and compact it. To make this task easier, the sand is moistened. Next, gravel is poured in and compacted as well. The surface of the pillow must be strictly horizontal; this can be checked using a level. A waterproofing material - roofing felt - is laid on top.

Monolithic MZLF

Next, the formwork is assembled. It uses boards or panel materials such as plywood, OSB and others. The board must be at least 5 cm thick. The boards are knocked down into shields. The formwork should be several centimeters higher than the expected concrete level. The height of the tape above the ground surface should be less than or equal to the depth and equal to 4 times the width of the tape.

The shields are fixed with pegs and connected to each other with self-tapping screws or nails. Fastening elements should not protrude into the formwork. If they end up in the concrete, cracks may appear or even a piece of concrete may break off. Also, the formwork for a shallow strip foundation is additionally strengthened with inclined supports (struts) made of timber with a cross-section of at least 5 cm. The supports are placed on the outside at a distance of approximately 0.5 m. It is necessary to drill holes in the formwork for communications. Pipes are inserted into them.

The inside of the formwork is lined with polyethylene for waterproofing and reducing adhesion to concrete. You can also use permanent formwork made of extruded polystyrene foam.

Reinforcement

The construction of a shallow strip foundation necessarily includes reinforcement. The reinforcement is knitted with knitting wire. The use of welding to connect rods is not recommended, as corrosion is most likely to occur in these areas. Reinforcement diagrams are shown in the figure.

The minimum number of rods for the frame of a shallow strip foundation is 4 pieces. Longitudinal reinforcement must be class AII or AIII, have a ribbed section. The longer it is, the better - each connection reduces the strength of the frame. For the transverse parts, thinner smooth reinforcement (6-8 mm) is used. For a shallow foundation, two reinforcing belts are sufficient, a total of 4 longitudinal rods. The reinforcement should be 5 cm from the edges of the foundation. There should be 30-40 cm between the vertical jumpers.

It is especially important to properly reinforce the corners. To do this, the rods are bent in such a way that the approach to the other wall is at least 40 times the diameter of the rod. In this case, near the corners the distance between the vertical jumpers should be half as much as in the wall.

Fill

It is better to take factory-made concrete, grades no less than M200 (for wooden houses) and M250 (for brick houses). When making it yourself, it is better to mix concrete not by hand, but in a concrete mixer.

It is advisable to fill the entire foundation in one go. Concrete is poured in layers, each layer is leveled and compacted. For this purpose it is better to use a vibrating rammer. The last layer is leveled according to the mark applied to the formwork. Professional builders who have already made dozens of foundations recommend sprinkling dry cement on top of the concrete. This is necessary so that the top layer sets faster. The foundation hardens for about a month.

Anti-heaving

Before you make a shallow shallow foundation on loam, you need to know that such soil requires anti-heaving measures:

• drainage,
• waterproofing,
• insulation.

For more information about foundation insulation, watch the video:

Important! It is very advisable to complete the entire cycle of work (build the house completely) in one season, so that the foundation does not remain without load during the winter. Otherwise, the forces of frost heaving can squeeze the foundation out of the ground, deform or break it. If it is not possible to complete the house before the cold weather, then the ground around the foundation must be covered with any heat-insulating material (straw, sawdust). There is no need to remove snow on the site.

MZLF on stilts

Foundations on piles are made on difficult soils. For this purpose, screw or bored piles are usually used. A sand cushion is poured under the tape. It will resist soil heaving.

Bored piles are made directly on the site. To do this, they drill wells, place pipes and reinforcing frames in them, and fill them with concrete. The depth of the wells should be below the soil freezing level.

The pile reinforcement must be connected to the tape frame. To do this, it must rise above the base of the tape by at least 40 cm. If screw piles are used, then holes are drilled in them, reinforcement is threaded through them and connected to the frame of the tape.

A shallow strip foundation, either monolithic or prefabricated, can be made independently. It can be used to build houses from different materials and different number of storeys (up to 3 floors), and it is used on different types of soil.

A classic for low-rise development is one with a low construction budget. The monolithic lattice structure allows floors to be built on the ground, has high spatial rigidity, and is suitable for any wall materials.

Shallow strip foundation step by step

The operation of any foundation is complicated by uneven heaving forces and insufficient design soil resistance. The technology became possible thanks to a set of measures to eliminate swelling:

• the topsoil layer is replaced with sand, crushed stone depending on the level of groundwater level
• the blind area is insulated to a width of 0.6 - 1.2 m
• the perimeter of the building is equipped with ring drains
• backfilling of trench sinuses is carried out with inert material

There is no heaving in non-metallic materials, excess moisture is removed by drainage, and the heat insulator retains the geothermal heat of the subsoil. It is better to carry out all work at the foundation pit stage in order to reduce the construction budget.

Calculation of parameters

Shallow strip foundation is not regulated in depth only if the above measures are taken to compensate for heaving forces. The calculated settlement must be within acceptable values, otherwise it is necessary to supplement the structure with bored piles. The standard parameters of the MZLF provide a 2-3 times greater load-bearing capacity for 2-storey brick cottages with an attic:

For MZLF tape, two reinforcement belts and anchoring in L-shaped and T-shaped joints are usually sufficient. Longitudinal rods 8 – 16 mm, reinforcement A400 (“corrugated”), clamps, anchors made of rods 6 – 8 mm smooth reinforcement A240.

Full-scale axle offset

Shallow strip foundation marked in a standard way. Instead of pegs, it is better to use cast-offs, consisting of two pointed bars with a crossbar between them. If you level all the cast-offs, mark with dashes the axis of the wall, the side edges of the tape, the cords can be removed during excavation work and tightened later to install the formwork. They are taken outside the perimeter of the MZLF (1 - 1.5 m) so that the soil underneath does not crumble. When breaking down you need to consider:

MZLF is not recommended if there is a height difference of one and a half meters between adjacent walls. The lateral movements of the soil are too significant; reinforcement of the belt with piles and retaining walls will be required, which will significantly increase the construction budget.

Trench development

Even with the maximum depth of the MZLF tape, all work can be done independently. Special equipment is needed for pits, but here you can get by with trenches. When excavating soil, common mistakes made by individual developers are:

Therefore, it is recommended to remove black soil from the entire perimeter with a bayonet. The dimensions of the pit are 1.2 m larger than the size of the foundation. This distance is necessary for insulating the blind area. Inside the trenches for the MZLF tape, additional trenches for drainage with a cross-section of 30 x 30 cm are required.

Drainage system

Clay soils swell only when they are abundantly wetted with groundwater. Drainage reduces heaving forces by 40% without additional measures. To create an underground sewer circuit, it is necessary to perform the following work:

To increase the service life of the system, the bottom layer of the natural filter is laid on geotextiles, with which the entire structure is covered on top after backfilling.

Substrate

Adding non-metallic material to the bottom of the trench is necessary to solve the following problems:

• leveling the base
• drainage to prevent concrete from getting wet
• elimination of heaving forces

Different regulatory documents provide different thicknesses of sand and crushed stone cushions, ranging from 20 to 80 cm or four times the width of the MZLF tape. In practice, a thickness of 40 cm is more often chosen, making it layer by layer (10 cm) with mandatory compaction (vibrating plate, rammer, wetting with water). You can alternate layers in any order, taking into account the distance from the base of the MZLF to groundwater.

Footing

A monolithic strip foundation is poured into formwork, which drains the concrete with a lower underlying layer with high drainage qualities. Some of the cement will leave along with the liquid, and the structure will experience a decrease in strength. Therefore, the following technology is used:

The footing allows you to reduce the protective layer (bottom) of concrete of the MZLF tape to 1.5 - 3 cm, lay a waterproofing carpet on top of it (2 - 3 layers of rolled material). The supporting surface of the foundation and the strength of the structure are increased, in which the cement laitance is completely preserved. It is convenient to mount formwork panels on the screed; you can additionally mark the axes. Plastic supports for fittings do not tip over when installing frames.

Reinforcement

When the height of the MZLF is from 70 cm (together with the plinth part), it is inconvenient to lay reinforcement cages inside the formwork. Therefore, first the tape is reinforced, then shields are installed around the frames. The work is carried out in stages:

The ideal option is to bend the rod 90 degrees, launch it onto the adjacent wall, and overlap it with the next rod. The adjacent rod in the same row, on the contrary, is launched from another wall so that the joints are located at a distance of 60 - 80 cm minimum. The lower, side protective layers are created by polymer parts placed on the rods at intervals of 0.7 - 1 m. The rods of one wall laid in the corners on the rods of the other without bending are considered an interruption of the reinforcing belt, even when connected by welding.

Longitudinal rods are made from A400 reinforcement with a periodic section of 8 – 16 mm. Anchors, transverse, vertical rods, clamps made of smooth 6 - 8 mm A240 reinforcement.

Formwork

Therefore, at shallow depths of MZLF, it is recommended to install formwork panels to the entire height of the tape with a 7 cm margin. When installing the top edge of the shield above the design mark, concrete is guaranteed not to splash out during vibration compaction and leveling.

Depending on the height of the foundation, the formwork panels are made of edged boards or plywood. This will allow the use of lumber after stripping at the stage of manufacturing partitions and roofing.

In the absence of an underground (floors on the ground), ventilation ducts in the MZLF tape are not needed. If beam ceilings are used, pipes must be installed in the formwork panels. The total area of ​​the vents should be about 1/400 of the size of the base part.

Concreting

The mixture is laid inside the formwork in layers, in one direction. The thickness of the layer depends on the size of the nozzle of the deep vibrator used for compaction. The normal quality of the tamping is indicated by the absence of large crushed stone, air bubbles on the surface, and the presence of cement laitance.

It is prohibited to drop concrete from a height of 1 - 1.5 m; gaps inside the formwork are larger than 2 mm. MZLF is characterized by small volumes of work, which makes it possible to fill the tape per appointment. If stage-by-stage concreting is planned, vertical partitions are installed in the middle thirds of straight sections. After pouring, the first three days require a wet compress (sawdust constantly moistened with water) or watering the surface from a watering can.

Protection of MZLF from moisture, soil heaving

After stripping, concrete structures are protected from moisture and swelling in several ways:

Volumetric or complex waterproofing is considered the most effective. In the first case, concrete is modified with special additives during mixing or impregnated with Penetron to impart moisture-repellent characteristics. In the second option, concrete structures are treated with a primer, coated with mastics, and covered with films, rolls, and membrane materials.

Shallow strip foundations (MSLF) are used in the construction of low-rise buildings from lightweight piece building materials. A relatively simple design, low material consumption and a high level of reliability make its use a technically optimal and cost-effective solution.

A structure of this type can be made by digging a pit around the entire perimeter of the house under construction or by digging trenches above the freezing point along the axes of load-bearing walls and partitions. The width and depth of the trench are determined by calculation (presented in gallery form towards the end of the article).

MZLF can be monolithic reinforced concrete or assembled from individual factory-made concrete blocks. It is possible to use rubble stone masonry or solid clay bricks, but the most durable and reliable structure is a reinforced concrete monolith.

MZLF scheme.

Conditions for using a shallow structure

The installation of a shallow strip concrete foundation (FMC) during the construction of a house will be advisable in the following cases:

• large depth of soil freezing;
• availability;

The lowest point of the foundation structure is always located above the maximum freezing level at a depth of no more than 1500 mm. Moreover, the greater the width of the base, the greater the weight load it can bear. The small depth of the MZLF allows it to rise with the house during winter heaving of the soil, while remaining intact.

Reduced load-bearing characteristics somewhat narrow the possible range of application of the structure and allow the use of a shallow strip foundation only in the case of building houses from light building materials, which include:

• wood;
• cellular concrete blocks;
• frame-panel products;
• lightweight masonry made of hollow bricks.

The width of the sole depends on the building material.

MZLF should not be used for the construction of large houses. The depth of soil freezing under the floor of such buildings will be less than in the adjacent area. As a result, winter swelling will be uneven, which can lead to structural failure.

The use of MZLF is prohibited on clay, peat and sapropel soils.

On weak and non-heaving soils.

On medium and highly heaving soils.

Conditions for calculating the foundation structure

In order to calculate the MZLF and determine the laying depth and width of the tape, it is necessary to take into account:

• type of soil to the depth of the calculated freezing point;
• ground water level;
• freezing depth;
• distribution of weight load on the foundation;
• height differences on the construction site;
• calculated depth, which is equal to the distance from the bottom point of the foundation to the zero level of the building.

The depth of possible soil freezing can be determined according to SNiP 23-01-99* “Construction climatology”.

If there are significant differences in height, it is structurally impossible to install an MZLF. In these cases, leveling the site or constructing a different type of foundation will be required.

The weight load acting on the foundation consists of a constant and variable component. Variables include snow and wind loads, the weight of engineering equipment, furniture, plumbing fixtures, etc. To determine the constant weight component, the height of the building, the materials used, the design of the roof and ceilings, and other design features are taken into account.

Design calculation

The reinforced concrete monolith of the foundation rises above the surface of the earth and rests on a cushion consisting of a layer of compacted crushed stone covered with a layer of sand.

Depending on climatic conditions, the depth of laying MZLF on heaving soils is determined by the requirements of SNiP II-B1-62 and is equal to:

• when freezing up to 1 meter - at least 500 mm;
• up to 1.5 meters – 750 mm;
• more than 1.5 meters – 1000 mm.

Therefore, builders usually make calculations for a shallow strip foundation, taking the laying depth as a value equal to the freezing depth, with a deduction of 20-25%. If this condition is met, the foundation for the house will be able to rise freely without destruction when the soil swells.

The height of the base above the ground surface can reach four times the width, but should not exceed the size of the underground part of the foundation.

The width of the structure under the load-bearing walls is equal to the mathematical ratio of the weight load (t/m) to the calculated soil resistance (t/m2), the value of which is given in the tables of SNiP 2.02.01-83.

The thickness of the crushed stone-sand cushion is determined according to the formulas and tables given in SNiP “Foundations and Foundations”. It depends on the degree of swelling of the soil, the thermal regime of the building and the material of the walls.

Expenses for the device MZLF

As practice shows, the cost of constructing a shallow foundation with your own hands depends on its size, design, elevation above ground level, number of lintels and some other factors. The average price is 5-6 thousand rubles. per linear meter.

Installation of monolithic reinforced concrete MZLF

After the design calculations have been made and the project has been completed, you can begin to make a shallow strip foundation with your own hands. The work on constructing the MZLF consists of several stages, which will be described in the form of step-by-step instructions:

• preparatory;
• marking;
• earthworks;
• pouring concrete;
• base devices;
• hydraulic and thermal insulation devices;
• adding sand and building a blind area.

To complete the work you will need the following materials:

• sand and crushed stone;
• cement M400 or M500;
• steel reinforcement with a diameter of 8 and 12 mm;
• knitting wire;
• boards for formwork or ready-made panel elements;
• bitumen and bitumen primer;
• brick for leveling the base part.

When installing thermal insulation for FMZ, you can use polystyrene foam, which is secured with glue and plastic nails.

Preparatory stage

Preparatory work includes clearing and possible leveling of the construction site. In this case, uprooting of stumps and bushes should be carried out together with the roots in order to exclude the possibility of their germination in the future.

All necessary materials must be delivered to the work site and stored in such a way as to prevent damage from adverse external influences.

Marking

To perform correct and accurate markings, it is best to use a construction level and a measuring tape at least 10 meters long. Using a level, you can easily determine the required directions of rotation angles of the foundation tape. This is especially important with complex configurations.

To tension the marking cord, it is necessary to make beacons and pegs. The beacon is a U-shaped wooden structure of two stakes and a crossbar, the width of which should be greater than the width of the foundation.

Initially, the tensioned cords must run along the edge of the outer wall of the MZLF, and after completion of the excavation work, before installing the formwork, they must also be tensioned along the internal contours.

Checking the markings is carried out by measuring the diagonals inside all rectangles. They must be equal for both external load-bearing walls and partitions.

Digging a trench

Marking and excavation work.

The required trench depth is equal to the sum of the depth of the reinforced concrete monolith and the height of the support pad. It is determined by the calculation described above.

For central Russia, the most commonly used design is with a cushion thickness of 200 mm and a recessed part of the foundation of 300 mm. In this case, the trench depth is 500 mm.

In order to prevent soil shedding and to have access to the surface when carrying out waterproofing work, it is necessary to make small slopes of 150-250 mm. Take the width of the bottom to be 200-300 mm wider than needed for the foundation itself.

Support pad for foundation

Sand pillow.

As a cushion, you can use ready-made crushed stone-sand mixtures (SCS), which are sold on the construction market for road work.

Another option is to layer-by-layer backfill with crushed stone and sand, carefully compacting each layer. In this case, crushed stone should be at least ¾ of the total thickness.

After installing the cushion, its surface must be covered with geotextiles.

This non-woven material is capable of transmitting moisture in only one direction and will protect the foundation from its effects.

In addition, geotextiles will stop possible plant germination towards the concrete part of the shallow foundation of the house.

A layer of crushed stone.

Formwork installation

The formwork structure for a shallow monolithic strip foundation is installed vertically, to the entire height of pouring the concrete mixture. In this case, part of it will be above ground level. It should be noted that concrete is not poured to the entire height of the foundation, since space should be left for a leveling layer of solid red brick.

To assemble the formwork, you can use boards or ready-made factory-made small-panel structures, which you can rent and not spend money on purchasing lumber.

The upper part of the formwork walls must be connected to each other by cross members, and the walls themselves must be supported by inclined slopes every half meter. This will make the structure more durable and prevent it from falling apart under the pressure of the concrete mixture.

Do not forget to install sleeves made of metal or asbestos-cement pipes. They will be required to enter utilities into the building. Since the MZLF is not a stable structure, the diameter of the sleeves must be at least 200 mm.

Formwork.

Structural reinforcement

Metal reinforcement increases the strength of the foundation several times and ensures its safety even in the most difficult operating conditions. From metal rods using knitting wire, it is necessary to tie blocks with longitudinal, vertical and horizontal strings and place them inside the formwork. In this case, the lower longitudinal strings should not touch the bottom of the trench.

It is possible to connect rods by welding, but this technology is more complicated and, when heated, reduces the level of hardening of the metal. The recommended diameter of the longitudinal rods is 12 mm, vertical and transverse 8 mm. After installing the reinforcing blocks inside the formwork, you can begin pouring the concrete mixture.

Reinforcement schemes.
Reinforcement.

Pouring concrete into the MZLF structure

There are two options for preparing concrete mixture. You can order it and buy it ready-made or make it yourself. The volumetric composition of a mixture of sand and crushed stone cement is determined as 1: 2.5: 4 for M400 cement and 1: 3: 5 for M500 cement.

Compaction of concrete is best done with a submersible construction vibrator. If it is not available, you can use a manual tamper, but in this case the concrete should be poured in layers of 30-50 mm and each individual layer compacted.

This way you can expel all air bubbles and ensure the necessary strength of the material.

If poured concrete hardens in hot and dry weather, it is recommended to cover the foundation with plastic film and periodically water it. The hardening time before masonry begins is at least 4 days.

Foundation protection

To protect a concrete monolithic structure from moisture, which can lead to gradual destruction, its surfaces are covered with hot bitumen and covered with waterproofing. Initially, the concrete is treated with a bitumen primer, which is used as a primer, and then waterproofing layers are applied.

Reduces heat loss of the building during the cold season and prevents the possibility of moisture freezing inside a monolithic reinforced concrete structure. Installation of insulation is a recommended, but not mandatory, condition for completing the work. This concludes our guide to building a strip foundation of shallow depth with your own hands.

Schematic cross-section: the insulation runs along the entire vertical wall of the tape combined with the base. Covered with cladding. The insulation should also be located under the blind area.
Photo of insulation.

Video on the topic

Foundation work is not considered the most complex construction work, but in terms of responsibility it is one of the most critical building structures. Most mistakes during foundation construction lead to very serious consequences; correcting them is very difficult and expensive, and in some cases impossible. All foundation calculations must be carried out in accordance with the provisions of SNiP 2.02.01–83.

File for download. SNiP 2.02.01–83. Foundations of buildings and structures. SP 22.13330.2011

During calculations the following are taken into account:

• loads acting on the base of the foundation;
• soil indicators, presence and location of groundwater;
• maximum permissible deformations and load-bearing characteristics;
• characteristics of climatic zones and foundation depth.

These are very complex calculations, we will not dwell on them. For the simplest structures, builders take standard parameters for a given climate zone and soil characteristics as the foundation. They already have a large margin of safety, which ensures the reliability of the design.

Shallow strip foundation - parameters

Introductory table of the approximate width of the strip foundation

Minimum tape width depending on the number of storeys	Tape width, cm The bearing capacity of the soil is 0.72 kgf/cm2. Example: silty, fine micaceous sands, silty sands, silty clay	Tape width, cm Soil bearing capacity 1 kgf/cm2 Example: clay, sandy clay, silty clay, silty inorganic silt	Tape width, cm The bearing capacity of the soil is 1.4 kgf/cm2. Example: sand, clayey coarse sand, silty crushed stone, clayey crushed stone	Tape width, cm Soil bearing capacity >1.92 kgf/cm2. Example: gravelly sand, gravel, crushed stone
Frame house 1st floor	30	30	30	30
Frame house 2 floors	38	30	30	30
Frame house 3 floors	58	43	30	30
Frame house, lined half-brick, 1st floor	30	30	30	30
Frame house, lined half-brick, 2 floors	53	40	30	30
Frame house, covered "half-brick" 3 floors	81	60	40	30
Brick house, 1 brick laying, 1st floor	40	30	30	30
Brick house, 1 brick, 2 floors	73	53	35	30
Brick house, 1 brick, 3 floors	106	81	53	40

Tape width depending on wall material

A shallow strip foundation is one of the most frequently used options in private construction; in all respects it satisfies most developers. The construction of the foundation can be divided into three stages: marking, digging a trench and constructing formwork, pouring concrete and leveling.

Let's look at each stage in detail. We will talk about the stages of construction of a shallow reinforced foundation on a sand bed.

The work must be done carefully and slowly. It’s better to lose an extra hour or two during marking than to have problems later with the finished foundation tape.

Step 1. Drive wooden pegs around the perimeter of the foundation. In order to align the dimensions and angles of the tape, you need to prepare a basic device in the form of small benches. Drive two pegs into the ground at a short distance from the corners of the foundation and attach horizontal boards to them.

Step 2. Strengthen the nails in the boards and tie ropes to them. Try to first check the angle between the ropes with an ordinary large square. This will give you an approximation of the foundation lines.

Step 3. Align the corners of the tape; they should be exactly 90°. This must be done by checking the diagonals. The dimensions of the two diagonals cannot differ by more than two centimeters. Such scatter can be easily removed during the construction of the building box.

Step 4. Do not remove the ropes; use them to carefully mark the position of the tape with a shovel; it is advisable to dig a trench as deep as the bayonet of the shovel (about 20 centimeters).

Step 5. Now you can remove the ropes and continue digging the trench. Decide right away where you will put the land. It can be taken outside the perimeter of the building or leveled under it. In any case, the fertile layer must be completely removed.

Step 6. The width of the trench is equal to the width of the walls of the building. If the soil on the site is dense, then there is no need to do formwork in a trench; if the walls are crumbling, then you will have to do formwork along the entire height of the foundation.

The depth of the trench is within 60÷80 cm, taking into account a sand cushion up to twenty centimeters thick.

Video - Marking for the foundation

Foundation marking schemes	Description

Manufacturing

You can use second grade edged boards or special waterproof plywood. We will take boards 20÷25 mm thick and 20 cm wide; to assemble the panels we will use slats and scraps of boards.

Step 1. Production of formwork panels. There is no need to make them very large; then it will be difficult to install and dismantle. The length of the shields depends on their height, but in any case, try to ensure that the total weight of the structure does not exceed 50–60 kilograms. This weight can be lifted without much effort by two people. Try to fit the boards without large gaps, nail the vertical posts at a distance of 50–60 centimeters. More accurate indicators depend on the parameters of the foundation tape.

Shields – photo

Use nails for nailing; self-tapping screws will not only increase the cost of the formwork, but will also create problems during its disassembly. Almost all lumber after dismantling the formwork can be used for further construction of the building, it is advisable not to damage it again. You are unlikely to be able to accurately calculate the length of the shields; leave a margin of approximately 1.5÷2 meters in length; you will make this shield after accurately installing all the previous ones. In this position it will be possible to take exact measurements up to the corner and make the shield of the required length.

Step 2. Start laying out the formwork for the foundation. This kind of work cannot be done alone; you need to call an assistant. Lower all the panels one by one into the trench, fix the position with pegs and corner stops. Spacers should be inserted between the panels so that they do not change their position while fixing the formwork. Spacers do not work while concrete is being poured, they are only important during the assembly of the formwork. We advise you to immediately prepare spacers for the template; the quantity is determined taking into account the length and height of the foundation strip and the parameters of the boards.

Step 3. Fix the panels securely; it is better to place corner supports more often than to level the foundation later. Place your shields along the rope and constantly monitor their position. The joints of the boards are sealed with a board; fastening must be done in this place. Drive the pegs as deep as possible; the corner supports to the shields must be fixed with special small stops made from scraps of boards. You must exclude even the slightest possibility of violating the integrity of the formwork while pouring concrete. Such an “accident” always comes at a cost.

Step 4. During the installation of formwork, it is always necessary to provide for its subsequent dismantling. This means that the nails should be driven into places where they can be removed. Place all dismountable units only on the outer accessible side of the formwork.

Step 5. Check that the formwork is installed correctly. Pay attention not only to the linearity of the planes, but also to the reliability of fixation. Apply multidirectional forces to the formwork - if even slight vibrations of the structure are detected, immediately install additional stops. Remember that correcting formwork installation errors while pouring concrete is an extremely thankless task.

Assembled formwork - photo

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Video - Making formwork

Step 6. Place plastic tubes in the formwork at the locations of ventilation ducts and utility lines. Secure the top boards of the formwork panels with boards or tie them with wire to prevent expansion.

Our foundation must be reinforced - its load-bearing capacity increases significantly. For reinforcement, construction reinforcement of periodic profile Ø 10 mm is used. The reinforcement can be tied together, which takes a very long time, but you can only lay horizontal bars while pouring concrete. We, of course, choose the second option. In terms of strength, a strip foundation loses almost nothing, and much less work and money will be required.

If everything is fine, you can start pouring concrete.

Pouring concrete

We will make the concrete ourselves from grade 400 cement, sand and gravel or crushed stone.

Nowadays, such heavy physical work is no longer done manually; you need to purchase or borrow a small concrete mixer with a drum volume of approximately 0.2 m3.

Before starting work, you need to calculate the required amount of building materials; calculations are made taking into account the total volume of the foundation tape. It’s easy to calculate the volume; multiply the length by the width and height. For one cubic meter of concrete you will need 325 kg of cement, 760 kg of sand and 1100 kg of crushed stone. These are approximate figures, they are needed only to guide the amount of materials. When purchasing materials, increase their quantity by 10%. You need to buy even more sand for a sand cushion.

No one weighs individual ingredients to the nearest gram when making concrete. When preparing concrete, take two shovels of sand and three shovels of crushed stone or gravel for one shovel of cement. Water is used as needed, the specific amount is determined experimentally, and the concrete must have optimal viscosity.

Step 1. Pour a layer of sand ≈15÷20 centimeters thick into the trench. The sand needs to be compacted well; use any available means for this or make a simple device.

Step 2. Pour the concrete mixture around the perimeter of the building, do not allow large differences in height. If you have an electric vibrator, great, it can compact the concrete along the entire height of the foundation. If tamping is done manually, then the concrete layer should not exceed 25–30 centimeters in height.

Step 3. Simultaneously with pouring, pay attention to the “behavior” of the formwork; if you detect any bulges or curvatures, immediately take measures to eliminate them.

Step 4. We decided that we would perform the foundation reinforcement in a simplified way. The rods are placed directly on the concrete. In total, we will have four rows of reinforcement in the tape, two in each layer. Cover the sand cushion with a layer of concrete approximately 30-40 centimeters thick. Level it horizontally and lay two rows of reinforcement. You shouldn’t try too hard, the rods will then become filled with mass, and a small angle of inclination (if any remains) will not have any negative effect.

Step 5. Continue pouring the foundation around the perimeter, when twenty to thirty centimeters remain to the top of the tape, lay the second row of reinforcement. Make sure that the ends of the reinforcing bars overlap by approximately 20÷30 centimeters.

Step 6. Align the zero level of the strip foundation; the variation in height in the corners cannot exceed two centimeters. Use a stretched rope; with its help you will perform the leveling faster and with better quality.

It is highly advisable to fill the entire foundation within one working day.

In most cases, this is possible for baths, but it all depends on the specific size, ability to organize construction work, professionalism and the number of workers. If you have to leave part of the work for the next day, then the liquid concrete in the formwork must be leveled horizontally as much as possible. The presence of “steps” with large differences in height significantly reduces the load-bearing characteristics of the foundation. The formwork should be removed two weeks after pouring the concrete. If the weather outside is hot and dry, it is recommended to moisten the concrete generously with water several times a day. A quickly drying foundation will not have the calculated strength indicators.

Why? Concrete is a unique material. Under ideal conditions, the strength of concrete structures constantly increases. During the first 14–15 days, concrete gains 70–80% of maximum strength, then the rate of increase in strength slows down and after 30–40 years its strength increases by only a fraction of a percent. But it is increasing! Of course, this only happens in cases where the structure is not affected by precipitation, temperature changes, external forces, etc. That is why it is not recommended to remove the formwork in less than two weeks. Do not rush to dismantle it; during this time it is better to prepare for the next stage of construction.

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Video – Seminar on pouring the foundation

Now that you already have a general understanding of foundation construction technology, you can give some practical advice. With their help, it will be possible not only to simplify and facilitate a number of construction works, but also to improve their quality and reduce cost.

How to make concrete

A lot depends on the proper organization of work; we give advice from experts who have solid practical experience.

The concrete mixer must be in a stationary place, and ready-made concrete is transported to the foundation by wheelbarrows.

There are some “craftsmen” who advise dragging the concrete mixer along the foundation as it is filled. They transport water, sand, cement and gravel separately in buckets to each new location. Looking at this “technology” is both funny and painful. This organization of work increases the labor intensity at least twice and increases the time by the same amount.

What do we recommend? The concrete mixer must be stationary; install it taking into account the possibility of access. Place a barrel of water with a volume of approximately 200 liters near the concrete mixer. Bring sand and gravel to separate piles, and let the cement lie on pallets in bags. All materials must be available for filling into a concrete mixer without transfer.

Throw a bag of cement onto the pile of sand and use a shovel to cut it approximately in half. Half a bag of cement is just the norm for one batch of concrete. Turn on the concrete mixer, pour one and a half to two buckets of water into it, take half a bag of cement with your hands and pour it into the water. You can immediately throw gravel or crushed stone; the pebbles will break up small piles of cement well. Next, throw sand and gravel into the mixer one at a time. The calculation is simple - for one shovel of cement you need two shovels of sand and four shovels of gravel.

The specific amount depends on the size of your shovels; for the first batch, you can measure the amount of cement in half the bag, this will give you a rough idea. In the future, you will gain experience and you will already be able to determine the quality of concrete by eye by the viscosity of the mass. If the solution is too thick, add water in small portions. If it turns out liquid, add sand; gravel has almost no effect on the viscosity of concrete; it absorbs little water. I had to add a lot of sand - throw another shovel of cement into the concrete mixer. The cement that spilled onto the sand is picked up and used.

With water, you also can’t guess right away; the amount of water depends on the moisture content of the sand and gravel. For the first batch, it is better to take slightly less water and then add it as needed. Too much water can cause trouble - there won't be enough volume in the concrete mixer to add large amounts of sand and gravel.

Ready concrete must be transported to the foundation by wheelbarrows. When planning the organization of work, it is necessary to provide for such a number of people that the work proceeds in an assembly line manner, without anyone expecting anyone. The time for pouring the foundation with concrete should be equal to the time it took to make it. These indicators are influenced by many factors: the distance to the foundation strip, the volume of the concrete mixer, the professionalism and hard work of the workers.

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Important

Perhaps this is all we can advise beginners; in the future you will gain your own experience and you will be able to change and improve the algorithm for making concrete.

How to assemble formwork

Absolutely all individual nodes work in bending or compression. Why are we talking about this? And then, when assembling the formwork, there is no need to use huge nails and then bend them five centimeters on the back side. Not a single nail works to pull out. In corner stops, the nails are subject to bending forces and very insignificant pulling forces. Using normal nails will not reduce the strength of the structure, but it will make your work much easier during its dismantling.

Most of the boards after formwork are used for further construction - after removing the formwork, immediately disassemble it and clean the boards. There are cases when high-quality boards are used for formwork - we recommend covering them with plastic film. Install the film on the inside of the formwork, fix it with an ordinary stapler. The cost of the film is pennies compared to the cost of lumber. No master will process boards contaminated with cement on machines, and polyethylene will keep the materials in their original condition.

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How to dig a trench

It would seem that nothing is simpler - dig deeper and throw further. But those who have never dug themselves think so. Each job has its secrets, here are just a few of them.

1. First you need to trim the grass roots along the entire length of the trench. Using a shovel, cut the turf along the line on both sides of the foundation strip to a depth of approximately ten centimeters. This will not only make it easier to remove the sod, but will also make the edges smooth.
2. The first excavated soil should be thrown away as far as possible from the edges of the tape. You will still have to throw it further than you might think. It's easier to do this before you get too deep. Over time, the trench will become deeper, and more effort will have to be spent to throw out the soil. And if you have already made a mound near the edges, then you will have to transfer it too.
3. Increase the depth by the spade bayonet along the entire length of the trench, immediately leveling the edges. Then clean up the loose soil with a shovel, starting work from the place where you finished digging with a bayonet shovel. This way you won’t be compacting the soil yourself. When you’ve finished clearing the ground, repeat it all over again, work with a bayonet shovel along the entire length, then clean the bottom of the trench.

Video - How to dig a trench for a foundation

We guarantee that in this way you will be able to dig the foundation much faster and without “heroic feats of labor.” It is impossible to talk about all the intricacies of construction work in one article. Do not perform monotonous work for a long time, this accelerates physical and mental fatigue; if possible, change it after an hour or two.

We can give one universal piece of advice: look for logic in every work. All actions should be aimed at one thing - obtaining maximum results with minimal losses. It doesn’t matter what the loss is: time, money or effort. If you listen to our advice, then work will always be a joy, not a punishment. Especially if it is done with your own hands and for yourself.

Video - Do-it-yourself shallow strip foundation

A shallow strip foundation (MSLF) is a type of strip foundation, which is located 0.3-0.7 m below the zero level. The construction of this type of foundation requires a minimum of financial and labor costs. MZLF is excellent for light buildings erected on various soils. The foundation has its advantages and disadvantages, as well as a special construction technology.

Shallow strip foundation: scope of application, pros and cons

The bearing capacity of MZLF, in comparison with foundations of other types, is assessed as average and largely depends on the type of soil on the site. A shallow foundation is suitable for the construction of country houses, timber buildings, frame houses, as well as outbuildings, bathhouses, barns, etc. For brick houses, large cottages made of foam concrete and aerated concrete blocks, a shallow foundation is not suitable. For such buildings, an excellent option would be a combined foundation on piles, for example, a shallow pile-strip type on bored supports.

It is advisable to build a foundation of this type on slightly heaving and non-heaving soils. The ideal option is sandy and sandy loam soils with low moisture content. The groundwater level must be at least 0.5 m below the laying depth. On clay, the construction of an MZLF is accompanied by difficulties, because Most clayey soils are classified as medium- and high-heaving soils. We will consider the features of constructing a foundation with a shallow laying depth on heaving soils below.

The advantages of this type of base include

• economical, concrete consumption is 30% lower than when constructing a conventional recessed strip foundation or a foundation with a monolithic floor slab;
• ease of construction, you can build it yourself without the involvement of workers and special equipment;
• small amount of excavation work - a narrow trench with a depth of no more than 0.7 m is dug;
• small area of ​​contact between the structure and the ground.

Among the disadvantages of MZLF they note

• pouring is carried out at stable temperatures above +10 C;
• limited use due to low load-bearing capacity
• construction is possible only on a flat surface with a slope of no more than 5 degrees;
• lack of a basement in the house.

Expert opinion

Sergey Fedorov

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If you are planning to build an MZLF foundation and “freeze” the construction, then keep in mind that you cannot leave the foundation unloaded during the winter! When the soil freezes, it will push out the monolithic tape, which will lead to a violation of its integrity.

Features of the design of a shallow foundation

A shallow monolithic strip foundation is erected on a flat surface. When building a house on a slope, you will have to combine MZLF with a pile foundation, using supports to level out the height difference. In terms of strength and resistance to deformation, the structure must comply with SNiP 2.03.01-84.

In cross-section, a shallow foundation looks like this:

Features of MZLF that must be taken into account during calculation and construction:

1. The depth of the foundation base depends on the depth of soil freezing.
2. Be sure to install a cushion made of dry bulk materials: a mixture of coarse sand and gravel.
3. When the groundwater level is high, drainage is performed under and around the foundation.
4. The base on which the monolithic tape is installed is compacted as much as possible.
5. It is necessary to arrange a blind area to drain rainwater and snow.

Taking these features into account, we can conclude that the backfill and blind area are an integral part of the shallow foundation. Requirements for the blind area are specified in SNiP 2.02.01–83.

Calculation of a shallow strip foundation

Calculating the MZLF, which is being built on low- and non-heaving soils, is not difficult. During the calculation, three main parameters are determined:

Laying depth

Determined on the basis of SN “Foundations and Foundations”. The document specifies the following minimum depth values ​​for the foundation base:

• when the soil freezes less than 2 m - 50 cm;
• when the soil freezes to a depth of 3 m - 75 cm;
• when the soil freezes more than 3 m - 100 cm.

For most regions of the middle zone, the depth of the MZLF will be 50 cm. For light buildings, such as a frame barn or a small country house, this parameter can be reduced to 30 cm.

Width of monolithic tape

In order not to make complex calculations, we recommend taking the width of the sole based on the table:

Wall and ceiling materials	Number of floors	MZLF sole width, m
Walls made of lightweight brickwork or aerated concrete with reinforced concrete floors	1	0,6
	2	0,8
	3	1,2
Timber frame walls with timber ceilings	1	0,4
	2	0,4
	3	0,6
Log walls with wooden ceilings	1	0,3
	2	0,4
	3	0,6
Walls made of timber with wooden floors	1	0,2
	2	0,3
	3	0,4

Height above ground level

The higher the monolithic strip rises above ground level, the better the floors of the house will be protected from dampness and cold. However, the height of the foundation to maintain stability and load-bearing capacity must correlate with its width. The best option: the height of the tape above the zero mark is equal to its width.

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Sergey Fedorov

Professional builder. 18 years of experience

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Example: The laying depth is 50 cm. The width of the monolithic tape according to the table is 30 cm. This means that the height above ground level will be 30 cm, and the height of the entire monolithic tape will be 80 cm. The height of the ground part of the MZLF should not be lower than the snow level. The snow depth value depends on the region (you can find it on the Internet). For regions of the middle zone, this value does not exceed 8-10 cm.

Calculation of MZLF on heaving soils

When building a house on heaving soils, more complex calculations are performed, the purpose of which is to determine the heaving deformation. It is quite difficult to make such a calculation yourself, so you need to entrust it to professional designers or use a ready-made table:

Name and degree of soil heaving	Number of floors of the building	Width of foundation base b, m	Thickness of the pillow t, m	Foundation design option	Reinforcement option
clays, loams and sandy loams, fine and silty sands, moist - medium sandy	1	0,3 / 0,2	0,6/0,7	G.	3
	2	0,3 / 0,2	0,5 / 0,6	G.	3
	3	0,3 / 0,2	0,4 / 0,5	G.	3
clays, loams and sandy loams, fine and dusty sands, moist - highly heaving	1	0,3 / 0,2	0,7 / 0,8	G.	4
	2	0,3 / 0,2	0,6 / 0,7	G.	4
	3	0,3 / 0,2	0,5 / 0,6	G.	4

In column 2 “Sole width” and column 3 “Cushion thickness”, the values ​​for heated and unheated rooms are indicated through the sign /. The column “Reinforcement option” indicates the minimum number of reinforcing bars that must be used to reinforce the monolithic strip.

Construction of a shallow foundation: construction technology

The technology for constructing MZLF is not complicated; filling can be carried out according to SNiPs 3.03.01-87, 2.02.01-83 or according to our instructions. The foundation for a frame house 10 x 10 m can be poured in 1-2 days. Before you start pouring, you need to decide where you will take the concrete solution. There are two options:

1. 1order concrete class B22.5...B17.5 at the nearest RBU. In this case, the mixture will be delivered to you at the specified time by a concrete mixer truck. If the ABS cannot reach the pouring site, then a special hose is used through which the concrete solution will be supplied to the formwork. Ordering a sleeve will slightly increase the cost of ABS services. In addition, you will have to pay for every hour of downtime of the special vehicle.
2. 2 prepare concrete yourself. At the same time, you will not depend on RBU and will spend significantly less money, however, the quality of the concrete mixture will be slightly lower. When mixing concrete, the recipe must be strictly followed. To prevent concrete from starting to set ahead of time, you can use special additives. You can begin preparing concrete immediately after installing the formwork.

Installation of MZLF: step-by-step instructions from A to Z

Preparatory work and marking

The installation of a shallow foundation begins with site preparation, which consists of removing debris and uprooting stumps. The top layer of soil with vegetation is cut off. If necessary, leveling and filling of soil is carried out, followed by compaction.

The marking is carried out as follows: the perimeter of the future foundation is established, beacon pegs are driven into the corners. Ropes are stretched along the future monolithic tape.

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Sergey Fedorov

Professional builder. 18 years of experience

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The diagonal between the corners must be strictly 45 degrees. You can check the evenness of the markings using a tape measure and a building level.

Construction of trenches and cushions

The depth of the trench depends on the depth of the foundation and the thickness of the cushion. The width of the trench is made 10 cm wider than the calculated thickness of the monolithic tape. This is necessary for installing the formwork. When constructing MZLF on loose soils, the trench slopes can be strengthened with boards. Pillowing is necessary to reduce the impact of frost heaving forces on the foundation. The thickness of the cushion, as a rule, is 20-30 cm for slightly heaving and non-heaving soils. For heaving ones - determined according to the table given above.

For corners where the walls of the future house intersect, it is necessary to strengthen the reinforcement frame by installing additional vertical rods, which are welded to the longitudinal rods. This reinforcement allows the strip foundation to withstand critical loads acting at the intersections of the walls.

You can lay the reinforced frame on a prepared cushion, but it is better to do it on the starting layer of concrete. The thickness of the starting fill should not exceed 20% of the entire height of the tape. Concrete pouring helps create a more even surface on which the reinforced frame is laid. If you decide not to fill the starting layer, then support fungi should be used to raise the reinforced frame above the surface of the pillow by 5-7 cm.

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Sergey Fedorov

Professional builder. 18 years of experience

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The reinforced frame should be located in space, nowhere in contact with the bedding and formwork.

Pouring concrete

Filling should be done at a temperature of +10 C and above. Before pouring, the formwork must be moistened, then the concrete will lie more evenly. The mixture must be poured in layers, the layer thickness should not exceed 40 cm, optimally 20-30 cm. Each layer is subjected to 5-10 minutes of vibration compaction. This technology does not allow voids to form inside the concrete. To supply the concrete mixture to the formwork, you must use an elastic sleeve or chute.

Layer-by-layer foundation pouring

After pouring is completed, the formwork is covered with a vapor-proof film. Hardening of the concrete lasts 25-30 days, after which the formwork is dismantled and the gaps between the foundation and the trenches are filled with soil.

Insulation of a shallow foundation

Professional builders recommend be sure to insulate the MZLF. It is recommended to do this immediately at the time of construction of the structure. An insulated foundation will protect the floors of the house from dampness and cold, which is especially important when arranging the floor “on the ground”. In this case, in the absence of thermal insulation, all the heat from the floor will go into the ground.

There are external and internal thermal insulation MZLF. External - when the insulation is attached to the outside of the monolithic tape, internal - from the inside. External insulation is considered mandatory, but internal insulation is usually done if the house has a basement. What insulation should I use? There are a lot of options. The most popular are:

1. Penoplex. Dense thermal insulation, excellent heat conservation. Its service life is significantly longer than that of conventional foam. Penoplex is resistant to rodents, mold and practically does not absorb moisture. In terms of price/quality ratio, this is the best material for thermal insulation of a shallow foundation.
2. Expanded polystyrene. The extruded material is slightly inferior to penoplex in terms of physical and mechanical properties. However, the price of polystyrene foam boards is 20-30% cheaper. It can be used in dry and dusty soils with minimal moisture.
3. Polyurethane foam. Liquid spray thermal insulation is an expensive option, but it has many advantages: no joints between slabs, a service life of at least 50 years, minimal water absorption and resistance to aggressive environments.

It is not recommended to make a prefabricated foundation on heaving soils. The forces of frost heaving will push out individual elements, which will lead to the destruction of the foundation.

If all work on the installation of FBS is carried out correctly, a small prefabricated foundation will last 70-80 years. This is exactly the service life that reinforced concrete blocks have.

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