The most popular and simplest type of foundation is the strip construction. For the construction of small one-story buildings, a simple strip foundation is enough, but for buildings of a multi-story type, an arrangement of a recessed base will be required.
Creating a foundation sunk into the ground does not justify itself in all cases. If such structures are equipped for low-rise buildings, the margin of safety will be used only by a third. It is advisable to build buried systems only for heavy buildings, as well as if the territory has difficult soil.
Material selection
Before you build a buried strip foundation, you need to select materials. These may be largestones from which the most reliable foundations are obtained. Reinforced concrete is an inexpensive material, but it is completely unsuitable for light sandy and rocky soils, as the structure can crack.
Brick strip foundations are only suitable for frame buildings. But a brick can only be laid to a shallow depth. If groundwater is high on the territory, such a foundation will not work. A universal solution is a strip foundation made of FBS. Any one-story building can be installed on the blocks.
Reinforced concrete foundation is considered to be the cheapest and most durable material. It allows you to build buildings of different configurations. One of the important requirements when using this technology is the competent selection of the mixture. Among other things, you will also need to carry out reinforcement.
Features of choosing a brand of concrete
Recessed strip foundation can be built from concrete. In order for the construction to turn out to be of high quality, you need to choose the right mixture, on which the durability and strength of the building will depend. The brand should be selected taking into account the weight of the building, the reinforcement used and the properties of the soil.
For small wooden structures or buildings based on a wooden frame, M200 grade concrete is suitable. If it is planned to build a heavier and bulkier building, it is recommended to use concrete grade M250 or M300. For a massive buildingM350 grade concrete should be used.
The choice of this component of the foundation also depends on the soil. If the soil is dense, then the M200 or M250 brand will suffice. But for heaving soil, in order to ensure sufficient frost resistance of the base, you should choose concrete grade M300 or higher.
Soil requirements
Recessed strip foundation can be erected on certain types of soil. The most suitable options are:
- rocks;
- clay;
- loamy soils;
- sandy soils;
- large clastic;
- stable soils.
The soil must not crumble. This suggests that work cannot be carried out on gravel or sand scree. It is also important where the construction sites are located. The smoother the site, the less effort and money will be required.
Preparation for work
Before you start building a deep strip foundation, you need to prepare. First, the layout of the base is carried out, which will insure against problems during the operation of the building. It is best to entrust the drafting of a construction organization. The foundation plan will need to be transferred to the site. A surveyor must be allowed to inspect the area.
Dig a trench when the marks are in place. If the building is small, then excavation can be done with a hand tool. For large-scale buildings, equipment is required - an excavator, after which the sides and bottom of the trench are manually leveledinstrument.
Expert advice
In order to make it more convenient to work, you need to make a small gap. All recesses in the soil must be made 10 cm wider than the foundation elements. This will make it easier to install the formwork. Gravel is poured to the bottom, which must be leveled, moistened and compacted. The thickness of the gravel should be about 25 cm. 120 cm of sand are poured on top with the obligatory tamping.
In order to protect the sole from moisture, it is necessary to lay a footing or a dense plastic film on top of the sand. In the first case, a pillow of sand and gravel is poured with a liquid cement solution. The materials are then well leveled and left for a week until everything sets well.
Installing formwork and laying reinforcement
If you want to build a strip foundation with your own hands, step-by-step instructions will certainly help you with this. During the construction of the described structure, a filling system is equipped. To do this, you need formwork, which is usually made of plywood or OSB sheet. Its thickness should be about 15 mm. You can use wooden shields from planed wooden boards. Their thickness must be 30 mm or more.
The height of the formwork should be such that it rises above the planned height of the foundation by about 100 mm. In order to prevent deformation of the structure during pouring, the shields must be additionally reinforced with spacers. Inside the foundation are plasticpipes. They are necessary in order to start communications through them in the future. So that they do not deform during pouring, they are filled with sand.
Features of reinforcement
In order to increase the strength and elasticity of the foundation, it is necessary to reinforce it with steel rods. Reinforcement of a buried strip foundation involves the use of a ribbed steel bar with a diameter of 14 mm.
The reinforcement configuration is selected taking into account the expected loads on the building. Reinforcement should be located above and below. You must install two horizontal belts. A knitting wire is used to connect the bars. But in order to ensure greater reliability of the system, welding can be used.
Concrete pouring stage
The construction of a buried strip foundation at the next stage involves pouring concrete. It is better to use ready-made concrete grade M200 or M300. It is recommended to order the composition, because otherwise you will need to do a great job.
In order to avoid stress lines between the layers, it is recommended to pour the solution from above. Otherwise, you will end up with the formation of layers with varying degrees of shrinkage.
Using a shovel at the beginning of work, you will have to distribute the concrete mixture, and then pierce the mass with a metal bar to remove the resulting bubbles. These manipulations are called bayonet. To save time, a vibrating compactor can be used instead of a metal bar.
The top edge of the foundationleveled after pouring, and then dried under a layer of polyethylene. Depending on the dimensions of the foundation, it is necessary to leave the foundation for a period of 7 to 12 days. After that, the formwork is dismantled.
Reinforcement rules according to SNiP 52-01-2003
If you decide to build a strip foundation with your own hands, step-by-step instructions for the work will help you with this. After reviewing it, you will be able to understand that it is better to follow the sanitary norms and rules that are mentioned in the subheading during the reinforcement process.
When choosing the distance between the rods, several factors should be taken into account, among them the cross section of the reinforcement and its location in relation to the direction of pouring concrete should be highlighted. It is important to consider the way in which the concrete will be placed in the formwork and compacted. Particular attention should be paid to the issue of the transverse relative position of the reinforcement. The step should be 300 mm or half the height of the rod section.
Special attention should be paid to the reinforcement of the corners. In this part of the supporting structure, reinforcement of a larger section is used. Her class must not be lower than third. Corners cannot be reinforced by overlapping, the reinforcement must be bent. When equipping a tape recessed foundation for a house, you will need to reinforce it using one of the existing schemes, namely:
- using L-shaped elements;
- use of U-shaped clamps;
- reinforcement with L-shaped collars.
The reinforcement is attached additionally. This indicates that it is necessary to anchorbent elements. Transverse reinforcement is installed 2 times more often in the corner anchoring area. We should not forget that the distance should not be more than 25 cm. This method is relevant for reinforcing prefabricated or monolithic strip foundations.
When observing the rules for reinforcing a deep strip foundation, you must remember that the width of the frame should be 2 times less than its height. The lower grid should be supported on pieces of concrete or brick. You can use ready-made underlays. The distance from the bottom mesh to the bottom of the trench should be 7 cm or more.
Laying depth
Depending on the massiveness of the building, the strip foundation must be laid to a certain depth. If this is a buried structure, and there is heaving soil on the territory, then the laying depth should be 30 cm more than the freezing depth of the soil. Under the internal walls, in the case of using heavy materials in the construction of a house, there is usually a less deep foundation.
If the premises are heated, then the depth of the foundation under the internal walls is calculated without taking into account the frost lines. But at the same time, you must complete construction during the warm season or take measures against freezing of the soil during work.
If you wondered what the depth of the strip foundation is, you should know that when calculating the dimensions of the base under the load-bearing walls of unheated buildings, the estimated depth of the soil freezing lines shouldbe increased by 10% of the average. For heated buildings, this value is reduced by 30%. If the building has a basement, then measurements must be taken from the floor.
If you are deciding how to properly make a recessed strip foundation, then it is also important to consider the type of soil. When there is sandy or dry soil on the territory, the foundation can be deepened above the freezing level of the soil. But the sole in this case should be no closer than 50 cm from the ground level. If the groundwater is close to the surface, and the foundation should have a greater laying depth, then a strip brick base is used.
In conclusion
When building the foundation for a house, each stage of construction is almost one of the most important. This also applies to formwork for deep strip foundations. 25 mm boards are great for her, which should be planed. This thickness will allow the material to withstand the pressure of concrete.
You should give preference to softwood boards, as they are characterized by elasticity and strength. For the convenience of work, prepare square wooden blocks, as well as pegs. The former will be used as spacers, the latter will be needed to fix the shields.
