How to calculate the size of the foundation

Calculating the size of the foundation for a house is a painstaking job that requires attention, because the quality of the above-ground part of the house depends on its accuracy. As a rule, there is a standard system, it was composed by architects, it is quite simple and should not be used for houses of complex construction, as there may be some discrepancies. If you want to learn how to do it right, read on ....

The most important task of each developer is to build a foundation that is durable and reliable, and in order to meet the requirements, select the appropriate geometry. To make it easier to calculate, look at the finished foundations that are ideally suited to your architectural plan. It is worth paying attention to the shape, quality and defects. They will tell you what mistakes were made at the time of construction.


After a visual inspection, you can safely proceed to a full calculation, which includes the values ​​of the carrying capacity and the deformation of the soil in the area where the foundation will be built. To do this, you need a knowledge of mathematics and physics.

The calculation of the bearing capacity is not complicated, difficult to deform - it should be made with professionals.

Take, for example, a strip foundation. The following data will be required:

  1. The quality of the soil.
  2. Groundwater flow rate.
  3. Mark of soil freezing.
  4. External load on the roof.
  5. Architectural project of the house.

With objective data, you can proceed to the phased calculation of the foundation.
The first stage is to determine the weight of the external structure of the house, which is above the ground, including the additional load from furniture, decorative finishes, etc., which will produce specific pressure on the plantar soil.
The second stage is geometry.
The third stage is the adjustment.

How to determine the size of the foundation for the house of economy class?

For this type of house it is necessary to determine:

  • the specific weight of the external structure, which is above the base of the foundation, and the weight of the ground itself should be taken into account;
  • basement, including decorative trim, floor and floor slabs;
  • wall panels, not including door and window openings;
  • partitions with external and external finish. A similar calculation is made directly with the walls;
  • roof system and ceiling, including decoration and roofing material;
  • stair flights;
  • insulation layer.

You will need a drawing paper, it will be necessary to sketch all the structural elements of the house. The sketch should be as close as possible to the actual structure. At the end of the sketches, the determination of the volume of the structure is made according to the formula - ДхВхШ = V. If it is necessary to determine the volume of a complex structure, it is necessary to divide the foundation into parts and calculate their volume using the proposed formula. The result is multiplied by the weight of the material of the structure. As a result, the weight of the structural element will be known, it must also be determined.
To find out the weight of the material, you need to multiply the resulting weight by preliminary calculations by the safety factor for the load.

Reliability factor depends on the nature of the load.

At the end of the summation of the weight of all the structural elements, the weight of the whole house should turn out; in the sketch it is designated - “Rk”. The dimension of the weight at home is indicated in tons or kilograms.

  1. Geometric parameters are determined taking into account the foundation depth, the parameters of the house plan, material, soil classification, as well as the planned structure.
  2. According to the final calculations, a diagram and a sketch are drawn up, where the width of the structure depends on the category of soil. It is worth noting that the width of the soil, regardless of the soil on which it is arranged, should not be less than 350 mm and less than the width of the walls of the house.
  3. The height of the house depends on the amount of immersion of the foundation in the ground.

To determine the snow load on the roof of the house, the standard formula is used - the Correction Factor X on the RS, as a result of which the adjusted snow load RS is obtained.

We recommend to read:

  • strip foundation for the house;
  • how to make a foundation for a bath.


We offer to watch a video about the mistakes of the foundation:

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