Types of foundations
By design features, the following types of foundations are distinguished:
- tape,
- solid,
- pile,
- columnar.
When designing, it is necessary to take into account the type of cottage, its area and weight, as well as weigh all the advantages and disadvantages of different types of foundations.
Tape
The most popular type of foundation for cottages is tape, which is determined by its versatility, good performance and affordable price.
It can be monolithic and prefabricated, but it is always erected in the form of a tape under load-bearing walls and partitions.
When installing a monolithic tape, the concrete solution is poured into the reinforced formwork. And the block design provides for the use of special FMS blocks. The precast foundation is suitable for dry soils, as there is a possibility of moisture ingress through the joints. Its installation requires the use of special equipment, so sometimes it turns out to be more expensive than a monolithic one. It is mainly used for timber and frame houses.
According to the depth of the deepening, the surface and the buried variants are distinguished. The deepened strip foundation for a cottage is mounted below the freezing depth of the ground and is used for heavy structures. For houses made of timber and lightweight prefabricated structures, shallow strip foundations are most often used, which requires less costs.
Solid
A monolithic foundation for a cottage provides good stability on soft and heaving soils. During the construction, it is possible not to carry out thorough geodetic surveys, since it does not require solid soil.
Such foundations are practically not buried, and the slab rests on a cushion of rubble and sand.
A strong base of 250-300 mm thick made of heavy grades of concrete ensures the reliability of the house, but such a structure can be unjustifiably expensive. Although this type of foundation has not lost its popularity for many years due to its merits. He:
- strong and durable,
- suitable for houses of any size and geometry,
- does not require the use of heavy machinery.
In some cases, it is worth considering the installation of pile foundations as an alternative.
Pile
For the construction of cottages from foam blocks and beams on loose and floating soils, pile foundations are the best option.
The advantages of such foundations are:
- less excavation,
- low material consumption,
- the water table is not important.
Piles made of steel, concrete and wood are placed to a depth of 10 meters, that is, they are buried below the freezing level to a solid foundation.
According to the installation methods, piles can be:
- hammered,
- printed,
- bored,
- screw.
Screw piles are often the only option for marshy and peaty soils, which are considered the most problematic.
The cost of a pile foundation and a strip deep bed is about the same.
Columnar
The foundation in the form of support pillars is intended for light houses, such as timber, frame and frame-panel houses.
It is widely used for single-storey cottages due to:
- low material consumption,
- lack of strict requirements for elevation differences on the site.
Pillars of concrete, brick, stone and wood are dug in along the perimeter of the base and at the reference points of intersection of the walls. The distance depends on the type of soil, the weight of the house and is usually 1.2 - 2.5 m. To support the basement, lintels made of bricks or basement panels are built between the posts.
The pillars are practically not buried in the ground, therefore, they are suitable for the construction of houses on dry soils, which are not subject to heaving and freezing.
Foundation on piles
It is quite understandable that for the construction of foundations of this type, piles are used, which act as the main supports. Consideration of the pros and cons of this foundation for a house should begin with the very definition of piles. So what are screw piles, what are they?
The popularity of pile foundations has recently increased significantly, since they have a high bearing capacity. Many specialized factories have recently begun to produce high-strength pile supports.
For example, a standard screw pile has a metal wall thickness of 4 mm. This is quite enough to withstand the effects of problem soils. Today you can already purchase supports with a wall of 6.5 mm. Thanks to this, the range of use of such bases for structures has become much wider, especially in industrial construction.
It is most advisable to arrange pile foundations on problem soils. These include clay, loamy, peat and boggy soils. If, under such conditions, you are engaged in the construction of a foundation made of reinforced concrete, then it will be very expensive. And it is the pile-screw foundations that can provide high strength indicators in such conditions, as well as an inexpensive cost.
Reinforcement of corners
In the design of the strip foundation, the weakest point is the corners and abutment of the walls. In these places, loads from different walls are connected. In order for them to be successfully redistributed, it is necessary to properly tie the reinforcement. Simply connecting it is wrong: this method will not transfer the load. As a result, after some time, cracks will appear in the strip foundation.
The correct scheme for reinforcing corners: either bends are used - L-shaped clamps, or longitudinal threads are made 60-70 cm longer and bent around the corner
To avoid such a situation, when reinforcing the corners, special schemes are used: the bar is bent from one side to the other. This "overlap" should be at least 60-70 cm. If the length of the longitudinal bar for the bend is not enough, use L-shaped clamps with sides of at least 60-70 cm.
By the same principle, the abutments of the piers are reinforced. It is also advisable to take the reinforcement with a margin and bend it. It is also possible to use L-shaped clamps.
Scheme of reinforcement of the abutment of the walls in the strip foundation (to enlarge the picture, right-click on it)
Please note: in both cases, in the corners, the pitch of the transverse jumpers is halved. In these places, they already become workers - they participate in the redistribution of the load
Reinforcement assembly technologies for strip foundations
Reinforcement of the strip foundation with your own hands begins after the installation of the formwork. There are two options:
-
The entire frame is assembled directly in a foundation pit or trench. If the belt is narrow and high, it is inconvenient to work.
- Sections of the frame are prepared near the pit. They are carried in parts and installed in their intended place, tying them into a single whole. It is more convenient to work this way, except that it is very inconvenient and difficult to transfer the connected structures from the reinforcement.
Both options are imperfect and everyone decides how it will be easier for him. When working directly in a trench, you need to know the procedure:
- The longitudinal rods of the lower armopoyas are laid first. They need to be raised 5 cm from the edge of the concrete. It is better to use special legs for this, but pieces of bricks are popular with developers. The reinforcement is also 5 cm away from the walls of the formwork.
- Using transverse pieces of structural reinforcement or molded contours, they are fixed at the required distance using a knitting wire and a hook or a knitting gun.
- Then there are two options:
- If contours molded in the form of rectangles were used, the upper belt is immediately tied to them at the top.
- If, during installation, cut pieces are used for transverse lintels and vertical posts, then the next step is to tie up the vertical posts. After they are all tied, tie the second belt of longitudinal reinforcement.
There is another technology for reinforcing the strip foundation. The frame turns out to be rigid, but there is a large consumption of the bar for vertical posts: they are driven into the ground.
The second technology of reinforcing the strip foundation - first, vertical posts are driven in, longitudinal threads are tied to them, and then everything is connected with transverse
- First, vertical posts are driven in at the corners of the tape and at the joints of the horizontal bars. The posts should have a large diameter of 16-20 mm. They are exposed at a distance of at least 5 cm from the edge of the formwork, adjusting the horizontal and vertical lines, and driven into the ground by 2 meters.
- Then the vertical rods of the calculated diameter are driven in. We determined the installation step: 300 mm, in the corners and at the junction of the walls it is half as much - 150 mm.
- The longitudinal threads of the lower reinforcement belt are tied to the racks.
- At the intersection of racks and longitudinal reinforcing bars, horizontal jumpers are tied.
- The upper reinforcement belt is tied, which is located 5-7 cm below the upper surface of the concrete.
- Horizontal jumpers are tied.
The most convenient and fastest way to make a reinforcing belt using pre-formed contours. The rod is bent, forming a rectangle with the given parameters. The whole problem is that they need to be made the same, with minimal deviations. And a large number of them are required. But then the work in the trench moves faster.
The reinforcing belt can be knitted separately, and then installed in the formwork and tied into a single whole already in place
As you can see, the reinforcement of the strip foundation is a lengthy and not the easiest process. But you can even cope alone, without helpers. It will take, however, a lot of time. It is more convenient to work together or three of us: to carry the rods and to expose them.
Step-by-step instruction
The assembly must go according to the instructions. For installation work you will need:
- fittings;
- sand;
- boards;
- bars;
- screws, nails;
- concrete solution.
After researching the site for construction, it is necessary to mark the site. Clarify the presence of cracks in the soil. They indicate heterogeneous ground. The presence of buildings on the site will help to assess the structure of the soil. You can also dig a strip in the area. When cracks appear, construction cannot be carried out.
To mark the site you will need:
- fishing line;
- roulette;
- pegs;
- hammer;
- pencil;
- piece of paper.
It is necessary to connect the pegs and connect them with a fishing line. Dig trenches on the pegs. Their depth is made more than the intended foundation.
Pay attention! Formwork is a form for the future foundation.
Wood can be used as a material for construction. It is lightweight and inexpensive. There are several types of formwork:
- small-panel;
- large-panel;
- adjustable;
- from blocks;
- relocatable.
Formwork installation:
- clean up the site;
- connect the shields as tightly as possible;
- check all formwork fasteners.
The concrete layer during pouring should be about 25 cm. In winter, fresh concrete must be insulated so that it does not freeze.
The main mistakes when bookmarking:
- inexperience and carelessness during installation;
- incorrect opinion about the composition of the soil;
- work with low-quality materials;
- the work of non-professional builders, which is expressed in the wrong markup;
- wrong timing for cleaning the formwork.
To avoid such mistakes, it is necessary to choose specialists and monitor the construction. You should not make a foundation in winter, as there is a high probability of cracking.
The main point in the construction of the foundation is the determination of its type, the exact calculation of the parameters. You must follow all instructions and heed the advice of professionals.
Buta base: pros and cons
It is worth noting, considering the rubble strip foundation, that this is the most optimal option for making the foundation for a variety of houses. First you need to study the main advantages and disadvantages of the design.
Cobblestone strip foundation - pluses:
- Excellent strength indicators - any rocks in terms of wear resistance will give odds to other building materials
- Resistance to moisture - the stone from which the foundation is built is constantly influenced by moisture and water in nature, but retains its properties and physical characteristics
- Environmental friendliness - which many types of other building materials (especially modern ones) cannot boast of
- Long service life of approximately 150 years
Cobblestone base - cons:
- A base made of rubble stone takes a long time - to lay out a row of masonry, you will have to spend a lot of time
- If it is necessary to attract employees, their services will cost a lot, taking into account the type of work
- Bout is expensive - about RUB 1,500 / t
- Before starting construction work, it is imperative to perform correct calculations.
Features of working with rubble base
When creating rubble foundations, you need to remember certain nuances. So, the first layer of rubble is laid out of stone only of the correct shape, the cobblestones are corrected with a chisel and a hammer. The strip base with butom is mounted with reinforcement at the corners of stones of the correct shape. Therefore, the number of cobblestones with parallel faces must initially be purchased large.
If the base is laid with a mortar of cement and gravel, the masonry must be done in layers: each layer of stone is poured with a cement layer, it is advisable to make the steps parallel. When a combined strip foundation is laid (blocks or bricks are used simultaneously with the quarry), the need for reinforcement with a wire with a cross section of 12 millimeters cannot be ignored.
In the process of designing the foundation, it is imperative to accurately calculate and think over the location of the ventilation ducts, and mount them correctly.
NZLF execution options
There are several ways to build an NZLF for outbuildings or a residential building in the country.
Precast strip foundation
Such a foundation is most often performed on low-loamy sandy soils. FBS blocks are used as material.
It is not recommended to equip a prefabricated foundation on heaving soils, because pushing out and subsidence of concrete blocks during frost heaving will be carried out unevenly.
FBS blocks are conveniently mounted due to mounting gaps and hinges, which significantly speeds up the assembly of the strip base.
Basic requirements for arranging a prefabricated foundation structure:
- a bedding is made under the base;
- FBS are installed in one plane;
- to connect individual plates, steel embedded parts are used (welded together) or a mortar based on cement grade M200 / 300;
- it is advisable to additionally strengthen such a foundation with a metal frame.
Advantages of precast foundation structures:
- ease of installation;
- minimal time spent on construction work;
- there is no need for the arrangement of formwork, preparation and pouring of concrete;
- low cost of construction.
Disadvantage: Heavy concrete blocks cannot be manually installed, therefore a construction crane must be hired.
Monolithic
Formwork is pre-assembled under a monolithic concrete base.Such a foundation can be used for the construction of private residential buildings on heaving soils, but with the obligatory filling under the foundation and the arrangement of an effective drainage system.
Differs in durability and stability on moving ground.
Advantages of monolithic NZLF:
- the possibility of erecting the foundation of any parameters;
- all construction work can be performed on their own without special construction equipment, the involvement of experienced workers;
- low cost.
Disadvantages: high labor costs, the hardening time of the concrete mass - up to 30 days.
Combined
An unsubmerged strip foundation can be combined:
- columnar base - the foundation tape is mounted on pillars dug into the ground;
- prefabricated monolithic base - part of the foundation is erected using FBS slabs, the other part is poured with concrete mortar using a formwork structure.
It is impractical to use combined base structures for small buildings.
Calculation of materials required for the construction of a strip foundation
For example, in a project to build a house with dimensions of 8 by 8 meters. To build the foundation of this structure, you will need a reinforced concrete structure, which consists of concrete. As a result, we need to calculate the amount of concrete required for the strip foundation.
To simplify the calculations, let's calculate the total amount of cement mortar for the construction of the outer box (internal partitions are not taken into account).
Foundation diagram
Formwork ready to pour
They usually start by determining the parameters of the foundation structure:
- Perimeter. It is necessary to determine the length of the future structure: we add 4 walls of 8 meters each and we get a value of 32 m.
- Width. It directly depends on the load on the base of the future box at home and can be determined by specialists. For the calculation, you can take a value of 40 cm.
- Heights. Experts determine this parameter taking into account the depth of soil freezing and its other characteristics. For example, it will be deepened by 1.5 meters, and the elevation above the earth's surface will be 0.5 m. The final height is 2 meters.
Next, we calculate the calculation of the concrete consumption. To do this, you need to find out how much it will take for 1 m: the height is multiplied by the width (2 x 0.4) and you get 0.8 cubes. The box will take (32 x 0.8) 25.6 cubes. To determine the partitions, it is enough to carry out a calculation according to a similar principle. The average cost of concrete for 2018 is about 3,000 rubles. It turns out that only the support under the box will cost 76,800 rubles.
Strip foundation for the house: laying depth
This question should become the most important in the design of the structure. The deepened strip foundation is supported so that its sole is 20-30 cm below the freezing mark. This is the only way to protect the building from uneven deformations during frost heaving.
The height of the strip foundation in this case depends on the climatic features of the area. The freezing depth is determined by the formulas. But with a simplified calculation of the dimensions of the support part, you can use ready-made tables developed for different cities of the country.
The depth of soil freezing in cities
The shallow design of the strip foundation assumes its laying at a distance of 70-100 cm from the surface level
It is important to remember that this option has a lower bearing capacity and is not resistant to the forces of frost heaving.
Before you start concreting for your house, you need to carefully choose the depth of support of the sole. At the same time, not only freezing is controlled, but also groundwater level. General rule: water should not be closer than 20 cm to the base of the building.
Low-rise building foundations usually do not need detailed calculations. All values are assigned by eye. In this case, there is a high probability of cost overruns. But if possible, it is better to turn to specialists who will accurately select the foundation, width and reinforcement. If this is not possible, use the minimum values:
- height depending on soil freezing;
- width, depending on what width is at the wall (the value for the foundation is taken not less, but preferably a couple of centimeters more);
- working reinforcement with a diameter of 12 mm;
- clamps with a diameter of 6-8 mm.
Work on a strip base from buta
To make a strip foundation from rubble stone, you need to choose a suitable site. Often, this type of base for a structure is used in places with difficult soils that are prone to swelling. Before starting the main work, you need to investigate the building site and study the hydrogeological features of the area.
It is necessary to pay attention, first of all, to the level of occurrence of groundwater, soil moisture, as well as the depth to which the ground freezes. And only then can you dig a trench
You must first mark the site using a regular tape measure or wooden pegs and twine. You can dig the moat yourself with a shovel, or you can use an excavator to work.
The size of the boulders directly depends on what the foundation will be. The walls of the trench should be several centimeters wider than the buta, since experts do not recommend laying the stone back to back. And the depth of the ditch should be at least one meter.
Shallow block foundation for a house with stone walls
Shallow strip foundation for a house with stone walls on medium-grained soils. 1 - monolithic reinforced concrete base of the foundation; 2 - sinus filling; 3 - sand and gravel anti-heaving cushion; 4 - reinforcing cage; 5 - blind area; 6 - backfilling the floor on the ground; 7 - horizontal waterproofing; 8 - house wall
The width of the basement of a house with stone walls is usually larger than the thickness of the walls. For these conditions, it is advantageous to make a monolithic reinforced strip of the sole of the prefabricated foundation of increased height. On top, on the bottom, lay out the underground and aboveground (basement) parts of the foundation made of small-format concrete blocks or bricks.
Pouring concrete with a monolithic basement sole directly into the trench, without formwork
On weak and medium-grained soils, it is advantageous to make the width of the trench equal to the width of the base of the foundation. Concrete is poured into the trench at the edge, without formwork. Previously, a reinforcing cage is installed in the trench. This method is suitable for sufficiently dense soils in which the vertical walls of the trenches do not crumble.
On medium-porous soils, sheets of insulation, extruded polystyrene foam 40 mm thick are fixed on the walls of the trench. A layer of insulation separates the concrete from the ground, which reduces the impact on the walls of the foundation of the tangential forces of frost heaving of the soil. This solution allows you to refuse backfilling the sinuses of the foundation trenches. In addition, the insulation increases the resistance to heat transfer of the basement of the building and reduces freezing of the soil under the base of the foundation. The insulation layer also serves as a foundation waterproofing.
For a house with stone walls, in areas without a strong slope, the bottom of the foundation it is enough to deepen to 0.3-0.4 m from the surface of the earth.
Commentary on the video. When pouring concrete directly into the trench, the monolithic foundation strip can be left without waterproofing. Lining the trench with foil, as some do, is not necessary. In this version, the waterproofing is arranged above, at the level of the masonry of the basement blocks.The protective layer of concrete between the ground and the reinforcement in the base of the foundation must be at least 70 mm.
The height of the base during construction in areas with high snow cover must be increased. For masonry of a high basement, it is advantageous to use concrete or lightweight aggregate concrete small-format blocks. Outside, the masonry is insulated with sheets of extruded polystyrene foam. When constructing a foundation on heaving soils, a layer of insulation is also laid under the blind area.
Sand cushion for prefab block foundation
A pillow of non-heaving sandy soil is always arranged under the foundation tape. On non-heaving and slightly heaving soils, the sand cushion serves as a leveling layer.
When constructing a foundation on medium and more heaving soils, the sand cushion is already anti-heaving. The pillow increases the bearing capacity and reduces the heaving deformations of the underlying soil.
For a non-buried foundation (in the figure), the thickness of the anti-heaving cushion is increased on medium heaving soils to 0.6 m. The width of the sand cushion should be at least 200 mm wider than the foot of the foundation (size b). from each side.
Prefabricated shallow-buried block foundation made of concrete blocks with increased base width