The foundation is the main component of any structure, as it acts as its supporting structure, on which the durability and safety of operation depend. Recently, for the construction of frame houses, cottages and household facilities, the installation of a shallow strip foundation is chosen.
It is ideal for all types of soil, is characterized by high strength, and work on laying it can be easily done with your own hands.
Shallow depth of the 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 block, expanded clay and wood. According to the requirements of SNiP, such foundations are not recommended to be erected 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 clay buildings, but the dimensions of the structure must be taken into account during their design. GOST also allows shallow strip foundations for unstable soil. Due to their design features, they can move together with the soil, protecting the building from possible shrinkage and destruction, in this they are inferior to the 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 site is carefully leveled, then the 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 is made with a thickness of 15 to 35 cm, its dimensions depend on the dimensions of the future structure.
In addition, the shallow strip foundation has some features that need to be considered when building it:
- the base is buried no deeper than 40 cm, and its width is 10 cm greater than the thickness of the walls;
- 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;
- with a high level of groundwater, it is necessary to provide for the installation of high-quality waterproofing and the installation of a drainage system;
- a shallow foundation requires warming from above, since the thermal insulation layer will protect the base from temperature changes and will serve as an excellent source of heat.
Advantages and disadvantages
Today, in the construction of buildings, you can choose any type of foundation, but the unfinished 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 in a sloping area where a buried version of the structure cannot be performed. The main advantages of such a basis are several characteristics.
- The simplicity of the device. Possessing even minimal skills, it’s quite realistic to lay the structure with your own hands without involving lifting mechanisms and special equipment. Its construction, as a rule, takes several days.
- Durability. Observing all the technologies and norms of construction, 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 basement and a basement. With this layout, reinforced concrete tape will serve simultaneously as a supporting structure and walls for the basement.
- The minimum cost of building material. For work, you will need only reinforcement, concrete and ready-made panels of wood for the manufacture of formwork.
As for the shortcomings, then some features can be attributed to them.
- Labor input. For construction, it is necessary to first carry out earthwork, then make an armored mesh and pour everything with concrete. Therefore, to speed up the installation process, it is advisable to use the help of the wizards, but this will incur additional costs.
- Simple to build. In the case when the laying is carried out in the winter, the concrete gains its strength later, after 28 days. And this means that you have to wait a month, since the foundation can not be loaded.
- The inability to build tall and large buildings. Such a foundation is not suitable for houses, the construction of which is planned from heavy material.
- The need for additional installation of waterproofing.
Before you start laying the foundation, it is necessary to carry out the design and make accurate calculations. The complexity of the calculations for a shallow tape base is to determine 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 plates will be determined.
In addition, in order to make the correct calculations, it is necessary to know the main indicators.
- The material from which the construction of the building is planned. The strip foundation is suitable both for a house made of aerated concrete, and for buildings made of foam blocks or timber, but it will differ in its structure. This is due to the different weight of the structure and its load on the base.
- Sizes and area of the sole. The future foundation must fully comply with the dimensions of the waterproofing material.
- The area of the outer and lateral surface.
- Diameter dimensions of longitudinal reinforcement.
- Mark and volume of concrete mortar. The mass of concrete will depend on the average density of the mortar.
In order to calculate the depth of the laying, it is first necessary to determine the bearing capacity of the soil on the construction site and the parameters of the sole 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 ceiling, door structures and finishing material.
It is also important to investigate the depth of freezing of the soil. If it is from 1 to 1.5 m, then laying is carried out at a depth of not less than 0.75 m, when freezing to more than 2.5 m, the base is buried to a depth exceeding 1 m.
The installation of the base for construction involves the use of high-quality building materials, and the shallow strip foundation is no exception to this. It is erected from a reinforced concrete frame on a sand cushion, while the calculation can be both monolithic and 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 frames, rods and nets are also laid in the thickness of concrete. The grid 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 base, they can withstand loads and stretch. Transverse reinforcement, as a rule, is performed using a smooth wire with a diameter of 4-5 mm.
Knitting wire is also used as an auxiliary material, it fixes the rods in the manufacture of mesh and frame.
To increase the life of the foundation, all elements of the reinforcement must be protected from external factors, for this, a gap of 30 mm is left between the edges of the rods and concrete.
In addition to the protective layer, the reinforcement is additionally laid on the supports, so both special stands sold in stores and pieces of steel or metal scraps can be useful for construction. During the laying of the foundation, the manufacture of formwork is provided, it can be purchased both in finished form and independently knocked down from wooden boards.
To fill the air cushion, medium-sized sand is used, and pouring is performed with concrete mortar of different grades. At the same time, concreting is best done with a high-grade mortar, grade M100 and higher.
The technology of installing a shallow foundation is not particularly difficult, so it’s 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 written down. In order for the foundation to serve reliably for more than a dozen years, it is important to pay attention to such moments as insulation, waterproofing and the frequency of fastening of reinforcement.
It is best if the foundation is monolithic.
It is also important to pre-make a geodetic assessment of the soil, which will determine the level of groundwater, soil composition and depth of freezing. The choice of the type of base and the depth of its laying will depend on these parameters. In the event that a budget construction option is planned, it is enough to simply drill several pits in different places of the site and independently examine the soil.
The soil, in which there is an admixture of clay, easily rolls into a ball, but if it forms cracks during formation, the soil consists of loam. Sandy soil cannot be rolled into a ball, as it will crumble in your hands.
After the composition of the soil is determined, you can proceed with the construction of the foundation. As a rule, a step-by-step instruction provides for the following steps:
- calculation of the cross section of the reinforcement, the width of the tape and drawing up a reinforcement scheme
- the manufacture of a pit for the basement or trench for buildings without a basement;
- installation of a drainage system and thermal insulation;
- installation of formwork and fastening of fittings;
- concrete pouring and installation of waterproofing after formwork.
The completion of laying the foundation is the insulation of the blind area, for this it is lined with a special material that is resistant to moisture. If all the points of the instruction are executed correctly, in compliance with the technologies and construction standards, the resulting shallow-deep 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.
The construction of the foundation should begin with the preliminary preparation of the land, it is thoroughly cleaned of debris, plants and trees, remove the fertile soil layer. Then marking is done and all measurements indicated in the building design are transferred to the work site. To do this, use pegs and a rope. First of all, the facade walls of the building are noted, 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 markup, a rectangle is obtained comparing all the diagonals.
The beacons are clogged in the corners of the future construction, observing a distance of 1 m between them. The next step is to install a wooden blind area, on which the ropes will stretch. Some craftsmen simply apply the dimensions of the foundation to the ground using a mortar. Then the trench digs, 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 with a width of 0.6-0.8 m and a depth of 0.5 m is made for a shallow foundation.
In the event that the project provides for the construction of heavy structures with stairs, a porch and a stove, it is recommended to dig a pit. For the manufacture of pillows 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, additional geotextiles must be placed in the trench.
The pillow is covered in layers: first of all, the sand layer is evenly distributed, it is well compacted, moistened with water, then gravel is poured and rammed. The pillow should be placed strictly horizontally and covered with waterproofing in the form of roofing material.
An equally important point when laying the foundation is the assembly of the formwork. To make it, use such shield materials as OSB sheets, plywood or boards with a thickness of at least 5 cm. In this case, the boards should be knocked down into the boards. The formwork must be calculated so that it turns out a few centimeters above the future level of concrete. 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 widths of the tape.
Prepared panels are fastened together with nails or self-tapping screws, after which they are additionally propped up with pegs. It is worth paying attention to the fact that all fasteners do not stick out and go inside the formwork. If you ignore it, then after pouring they will be in concrete and can provoke the appearance of cracks or chips.
The formwork of the shallow-deep strip foundation is also additionally strengthened by struts made of a 5-cm cross-section beam, such supports are placed externally at a distance of 0.5 m.
In addition, in the formwork, it is necessary to prepare holes for communications in advance and insert pipes. The inner part of the structure is covered with polyethylene, it will enhance waterproofing and reduce adhesion to concrete.
It is also possible to use a fixed type of formwork made of extruded polystyrene foam.
A device of this type of foundation includes mandatory reinforcement. The fittings can be either knitted with wire or welding can be used, but for connecting metal rods, the latter option is not recommended, as corrosion will appear at the attachment points over time. For the installation of the frame requires a minimum number of rods, at least 4 pieces.
As longitudinal reinforcement, it is necessary to use a material with ribbed section of class AII or AIII. Moreover, the longer the rods, the better the frame will be, since the joints reduce the structural strength.
The transverse parts of the frame are assembled from smooth and thinner reinforcement with a diameter of 6 to 8 mm. Two reinforcing belts consisting of only 4 longitudinal rods will be sufficient to install a shallow base. It is important that the edges of the reinforcement extend 5 cm from the foundation, and the pitch between the vertical fasteners is at least 30-40 cm.
The crucial moment in the work is the manufacture of the corners of the frame: the rods must be bent so that the approach to another wall is at least 40 mm from the diameter of the rods. In this case, the distance between the corners formed by vertical jumpers should be two times less than the distance in the wall.
The completion of the installation of the foundation is concrete pouring. Specialists recommend using factory grade concrete of at least M250 for this. If the solution is to be made independently, then a concrete mixer should be prepared in advance, since it will be difficult to do it manually. The base must be poured with a solution immediately, for this it is evenly distributed over the entire surface and compacted. Each fill layer should be carefully aligned with the mark on the formwork.
Experienced craftsmen who made more than one hundred foundations advise sprinkling concrete with dry cement at the end of the pouring, this will improve its quality and the top layer will set faster.
As a rule, one month is allotted to complete solidification of the foundation, after which construction work can be continued.
Since the foundation is the main component of any design, its laying must be done correctly, especially with a shallow tape base, which is installed on loose soils and clay soils. Any mistake made during its construction can nullify all construction work. When making the foundation yourself, inexperienced craftsmen make several common mistakes.
- They begin construction without calculating the basic dimensions and load on the foundation.
- Pour the base immediately into the ground, without sprinkling and making a sand pillow. As a result, in the winter season, the soil will freeze to concrete, drag and lift the tape upward, as a result of which the foundation will begin to heave under the influence of frost, and the floor of the basement will crack. This is especially true when 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.
- Carry out construction in more than one season. The entire cycle of work should be distributed so that the laying of the foundation, laying of walls and insulation of the blind areas are completed before the onset of cold weather.
In addition, the protection of a concrete base with a film is considered a big mistake. Do not close it. The poured solution must have access to ventilation.
See how to make a shallow ribbon foundation with your own hands in the next video.