Building a garage is often perceived as a simple task that does not require serious engineering training. However, it is precisely foundation-deepness It is a critical parameter that determines whether your structure will stand for decades or crack after the first winter. Errors at the stage of laying the foundation is almost impossible to correct without a complete restructuring, so the calculations should be approached with the utmost care.
Many landowners try to save money by relying on the advice of neighbors or universal tables from the Internet. This is a dangerous approach, because geologic conditions Even within the same area can be very different. The level of groundwater, soil type and terrain terrain dictate their own rules, ignoring which will lead to deformation of the walls and distortion of the observation pit.
In this article, we will analyze all the nuances that affect the depth of the laying, and help you choose the best type of foundation for your particular case. You will learn how to save on materials without sacrificing strength, and what standards SNiP really important to comply with when building light buildings.
Factors affecting depth of storage
The first thing to determine before starting the excavation is soil-type on your precinct. Pulled soils (clay, loam, soup) increase in volume when freezing and are able to push a light garage up, and when thawing - lower unevenly. For such soils, the depth of the foundation sole laying should be below the calculated depth of freezing or compensated by insulation.
The second critical factor is groundwater level (GW). If the water comes close to the surface, a standard belt foundation can turn into a tank that will constantly erode the concrete. In such cases, it is often necessary to abandon deep foundations in favor of plate structures or piles, which changes the entire construction estimate.
⚠️ Warning: Never rely on visual inspection of the soil. In spring, the water level can be one, and in autumn – completely different. Order geological exploration or check with neighbors whose garages have been standing for more than 10 years.
The weight of the design itself also plays a role. Heavy brick or block garages require a more powerful and deep base than lightweight frame structures made of flooring or sandwich panels. For heavy walls foundation-sole It should be based on dense, non-surface layers of soil.
Standards of depth of freezing by region
The depth of freezing (GPG) is a reference value that varies depending on the climatic zone. In the northern regions it can reach 2 meters or more, while in the south it is only 50-70 cm. Knowledge of this figure is necessary for the correct calculation of the depth.
Below is a table with indicative values of the depth of freezing for different types of soils in different regions of Russia. These data are averaged and need to be adjusted for a specific location.
| Region | Clays and loams (see para. | Small sands (cm) | The sands are large (cm) |
|---|---|---|---|
| Moscow and the region | 120–130 | 130–140 | 140–150 |
| St. Petersburg | 120–130 | 130–140 | 140–150 |
| ekaterinburg | 160–170 | 180–190 | 200–210 |
| Novosibirsk | 180–200 | 200–220 | 220–240 |
| krasnodar | 60–80 | 80–90 | 90–100 |
It is important to understand that under the heated garage the ground freezes less than in the open space. If you plan on floor-insulation and constant heating, the calculated depth can be reduced by applying the coefficients of thermal influence of the building.
Types of foundations and their depth requirements
The choice of the type of foundation directly dictates the required depth of the trench. There are several basic options, each of which has its own installation features and requirements for burying.
- 🏗️ The ribbon foundation: Classic solution. The depth depends on the GNG. For pulpy soils, deepening below the freezing point is required, for non-pulpy soils, 50-70 cm is enough.
- 🧱 Table foundation: Monolithic slab. Often it is made shallowly buried (20-40 cm) with a mandatory insulated pavement, which allows you to "swim" together with the ground.
- 🪵 Pile-screw: Ideal for complex soils and slopes. The depth of screwing is determined by the length of the piles and should reach dense layers, usually from 1.5 to 3 meters.
- 🧱 Pillars: Suitable for lightweight garages. The poles are buried below the GNG, but require high-quality roasting for load distribution.
Shallow-deep ribbon foundation (MZLF) is a popular option for single-storey garages. Its depth is usually 40-60 cm, but it requires a mandatory device of a sand cushion and perimeter insulation. This allows you to save up to 50% of concrete compared to a deep-deep analog.
Why can't you save on a sand pillow?
Sand cushion thickness of 20-30 cm performs the function of drainage and compensator bloating. Without it, the forces of the frost beam will be transmitted to the concrete directly, which will lead to cracks even with proper damping.
Calculation of depth for different types of soil
The soils are divided into fuzzy and non-puzzy, and the approach to them is radically different. On rocky and coarse soils, the depth of freezing is not crucial, since they do not expand when freezing. Here the foundation can be laid to a depth of 50 cm, the main thing is to remove the fertile layer.
On clay and loamy soils, the situation is more complicated. If the groundwater level is high, the water in the clay pores freezes and expands. In this case, depth It should be below the GNG. The alternative is to replace the ground under the foundation with a sand mixture or insulation to shift the freezing line.
If you are building on highly bundled clay, consider insulating the cap and screening with extruded polystyrene foam. This will make the foundation shallowly buried even where, according to the norms, you need to dig deep.
Sandy soils, especially large and medium-sized, practically do not thicken. However, they can be subsident. In such cases, it is not so much the swelling as the even distribution of the load and the prevention of sand leaching by groundwater.
Stages of preparation of the pit and laying
The process of creating a foundation does not begin with a dike, but with marking. Errors in geometry at this stage will be extremely difficult to correct. After removing the fertile layer of soil, it is necessary to level the bottom of the trench.
The next step is to create a pillow. A layer of sand (15-20 cm) is filled to the bottom, spilled with water and trampled. Then there is a layer of rubble (10-15 cm), which is also compacted. This multilayer structure provides water removal from the sole of the foundation and reduces the impact of the bloating forces.
The formwork is set according to the height of the cap. It is important to strictly observe the verticality of the walls. Reinforcement is made in two belts (upper and lower) for belt foundations. Concrete must be continuously applied to avoid the formation of “cold seams” that reduce the strength of the structure.
⚠️ Warning: Do not pour concrete into dirt or water. The bottom of the trench shall be clean and dry. The hit of clay in the concrete mixture critically reduces the mark of strength of the finished foundation.
Frequent errors in determining depth
One of the most common mistakes is building by eye. Owners often dig a trench 30-40 cm deep, believing that this is enough for a light garage, even on clay. After 2-3 winters, such a garage is swayed, the doors stop opening, and cracks are on the walls.
The second mistake is ignoring the water level. The foundation laid above groundwater level without high-quality waterproofing is rapidly eroding. Concrete has a capillary structure and “drinks” water, which, frozen inside, tears it from the inside.
The third mistake is the lack of insulation of the windows with a shallowly buried foundation. Without a thermal circuit, the ground under the foundation freezes deeper than