What difficulties will you have to face when building a foundation for a house with a basement?

Before starting the design of the foundation, you need to decide on the basement device. This is an important stage, since the type of support part and the depth of its laying depend on the decision whether or not to make an underground floor. The foundation for a house with a basement with your own hands is a responsible and costly event, so you should take the issue seriously.

The main factor that influences the decision to build a house with a basement or basement floor is the price of the issue. Most often, monolithic or is used for such construction. When doing work with your own hands, you can thoughtlessly decide that the cost will increase only due to the price of the material, but this is not the case.

Indicators that will affect the estimate:

Excavation. There is an increase in the depth of the laying. In addition, if there is a basement or basement floor, it becomes necessary to make a foundation pit instead of a trench. When deepening the sole of the strip foundation, it is necessary to take into account the angle of repose of the soil. This value shows what slope should be at the walls of the trench or foundation pit so that they do not collapse without additional reinforcement. The smaller the angle of repose (internal friction), the more soil will have to be removed.
Transportation of soil. This factor follows from the previous one. The more material is removed, the larger the equipment and the more time it will take to take it out of the house construction site with your own hands.
... The technology of this stage becomes more complicated. In the absence of a basement, it is enough to cover with bitumen or apply high-quality concrete. In this case, a waterproofing device is required from more modern materials, such as linokrom, waterproofing, glass insulation, membranes. To protect the waterproofing layer from destruction during compaction and deformation of the soil, it is necessary to make protection against mechanical damage. For this, brick walls are erected or a layer of extruded polystyrene foam (foam) is fixed.

All these factors increase the cost of making a strip foundation for a house with a basement with your own hands, therefore, when making a decision, it is recommended to draw up a detailed estimate and reasonably assess financial capabilities.

The main enemy of the basement is water

In some cases, building a house with a basement with your own hands is impossible without additional measures that will protect the foundation from soil moisture. Before starting the construction of a house, you need to do detailed geological research with the involvement of specialists. They will allow you to identify the exact level of the location of groundwater, the likelihood and frequency of their rise.

If the groundwater level (GWL) is located far from the earth's surface, it is sufficient to provide the following types of moisture protection:

vertical (coating, pasting with protection from damage);
horizontal at the level of the basement floor (closed with the vertical);
horizontal along the edge of the foundation.

Important! The minimum distance from the groundwater level to the base of the foundation is 50 cm. If the water in the area lies less than 2-3 meters from the surface, difficulties will arise.

To protect the supporting part of the building from moisture at a high ground level, the following measures are provided:

Gravity drainage is suitable for eliminating the upper water in elevated areas. It is laid at the level of the sole or below and is diverted to the nearest body of water or to an open area.
Forced drainage is used if it is necessary to make dewatering for flat or lowland areas. In this case, the system is equipped with a well with two pumps (one main and one backup in case of emergency). A device of this type of dewatering requires constant additional costs during the operation of the house.
External insulation with a pressure wall. It is a system of a vertical layer and a horizontal one located in the basement or basement floor structure. The technology requires that the system be closed, that is, the horizontal waterproofing is connected to the vertical one.

Important! The device of any type of drainage makes sense if the water rises during periods of heavy rains or floods. With a constantly high level of moisture, the drainage system will not cope with the load.

Basement for the whole house

This option is the most common. When erecting, it is important to remember the following points:

waterproofing (discussed in detail earlier);
drainage system (arranged even in the absence of the likelihood of flooding as a safety option);
insulation (when laid below freezing, it is not required by the standards, but it is laid for additional protection);
vapor barrier (provided together with water protection).

Penetrating waterproofing is not capable of providing vapor protection and is therefore not recommended for new construction.

Basement under part of the house

An undesirable option that involves a lot of difficulties. You cannot do without the professional help of a designer, so if you want to make the basement completely on your own, it is better to dwell on the previous version.

There are two options for the location of the underground part of the house with a strip foundation:

under an outbuilding, garage or protruding part of the building;
under the building spot.

The construction of the first option should be preferred, since it provides greater structural reliability. In this case, one dangerous place arises: the connection of foundations laid at different elevations. Part of the main underground structure rests on developed soil, which is different in density from that existing on the site.

Soils of different degrees of compaction are dangerous in that they give different shrinkage. It is worth knowing an important thing: the house rests on the soil, not on the foundations. Structures only transfer this load. If the density of the base in different parts of the structure is different, cracks will appear, which are problematic to eliminate. The place where shrinkage cracks appear is the junction of the walls and foundations of the extension and the main part of the house.

To avoid an unfavorable phenomenon during the construction of a basement under an extension, the following methods are used:

Creation of a rigid structure that can withstand shrinkage. A detailed calculation of the strip foundation is required, as a cantilever beam with the installation of additional reinforcement in the upper zone (usually the reinforcement is installed evenly or with a larger diameter in the lower part). Only a constructor can do this work. In this case, the location of the likely occurrence of cracks becomes unknown. They can form in any weakened area where mistakes (even minor) were made during construction.
... To prevent the appearance of a crack at the junction of volumes with different depths, it is sufficient to make them independent of each other. The expansion joint is a gap, while the wall in its place can be either double or single. Double will require additional costs, but it will be a more reliable solution. The gap width is assumed to be at least 40 mm.

When designing a basement under the building spot, not one weak point is formed, but several (the number of joints increases). The strip foundation is considered as a multi-span beam. To ensure reliability, perform the following actions:

in the foundation along the entire building along the boundaries of the basement, a monolithic rigid belt is poured;
perform a thorough compaction of the basement backfill soil.

Important! The density of the backfill must be identical to the existing subfloor. Not more dense or loose. If this condition is not met, uneven shrinkage will occur, and cracks will appear.

Backfill compaction depends on the type of soil in the area. For sands or loose substrates, water spillage may be sufficient. If the house rests on dense soil, work is done in the following order:

laying a layer of sand no more than 30 cm thick;
moisturizing it;
backfilling of a thin layer of crushed stone;
compaction by platform or surcharge;
repeating actions from point one until the required thickness is reached.

Height difference

The weak point is worth telling in more detail. When constructing a difference in the marks of the support of the foundations, it is not recommended to do it at one time. It is better to divide the process into several stages:

pouring a slab under the basement;
raising the walls of the underground part by a third of the height (in a monolithic version or from prefabricated blocks);
pouring a monolithic stiffening belt, which will protrude beyond the walls of the basement by 60-90 cm;
raising the walls by another third of the height;
pouring a reinforced concrete belt under the foundation tape (is a continuation of the stiffening belt);
production of tape (parts without basement);
continuous reinforced concrete belt along the edge of the foundation.

The result is a stepped transition, which allows you to reduce the soil compaction zones and better distribute the load. The basement strip and basement walls can be made from blocks or from a monolith. In this case, it is important to perform structural shear calculations and lay additional reinforcement in the upper part of the cantilever protrusions.

Basement design is a task that needs to be carefully considered. When deciding to equip a room under a part of the house, it is important to remember that the most reliable and less labor-intensive option will be the following: a basement under an extension, separated from the main building by an expansion joint.

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