Minimum height for plinth. House base height

The construction of concrete foundations in Moscow, the region and throughout the country begins with a detailed and technically correct calculation of all the nuances and features. To establish the main characteristics of the foundation of the cottage, the design of the cottage, the features of the relief and soil conditions must be taken into account, and the meteorological situation in each specific region is also taken into account. All these subtleties are needed to calculate the height of the foundation in its above-ground part - that structural element on which many try to save money.

InnovaStroy specialists, based on the requirements of GOST and SNiP, create such structural elements that, on the one hand, will save the developer money, and on the other, will ensure the safety of the building, its load-bearing structures and finishing, no matter what materials they are made of.

The height of the foundation above the ground - what is it?

As you know, the foundation of any cottage is buried into the ground to a certain distance, depending on the design features of the building, design loads, characteristics of the soil base and the location of groundwater. Naturally, the underground part of the foundation can be of very different depths, up to 1.2 meters with no space involved. With the creation of a basement or equipped basement, this depth can reach 3 meters. The question naturally arises about that part of the base that protrudes above ground level - that is, above the zero height mark. Many believe that this part can be neglected and save significant funds on more than one cubic meter of monolith or brick.

In fact, those few tens of centimeters separating the surface of the earth from the beginning of the load-bearing walls are designed to provide increased protection of the entire structure from adverse external influences. The height of the foundation above the zero level is determined at the design stage by our architects and designers. This part of the building’s foundation is treated in the same way as all other elements - waterproofing, insulation, decorative external cladding. But in addition to aesthetic beauty, the basement distance also carries a functional load, which we do not recommend discounting if you want your country mansion to last for a very long time and not require repairs.

The height of the foundation of the house: why is it needed?

The distance from the ground to the lower edge of load-bearing walls and external decoration is designed to provide several protective functions at once, for which it is actually created by architects and designers. Below we will describe the main functions of the basement, without taking into account the option with a full basement, since in this case, according to GOST, more than 1 meter of distance from the ground to the first floor is required. So, the main functions of the above-ground part of the foundation:

Leveling the terrain of the site without making changes to the topography of the territory, with the absence of large volumes of earthworks. For very large differences in site elevation, it is best to order a pile foundation in InnovaStroy to minimize any excavation operations;
Resistance to heaving of the soil layer during the freezing process - thus, the soil acts only in the horizontal direction on the base walls, and does not apply force to the load-bearing structures of the walls of the cottage;
Protection against waterlogging during critical amounts of precipitation. Since the above-ground part of the foundation is slightly recessed in relation to the plane of the wall, it is easier to drain rainwater and condensate from the walls, which helps prevent the appearance of dampness and mold;
A certain height of the foundation above the ground allows you to minimize the impact of capillary moisture and evaporation. During the process of atmospheric exposure, microscopic pockets of moisture appear in the surrounding space and territory - dew, for example - they evaporate and can have a detrimental effect on the house, settling on surfaces. The distance from the zero construction mark allows this type of moisture to be removed into the drainage system even before it settles on the walls themselves;
The height of the house's foundation ensures that there are vents in the base to improve ventilation of the subfloor space. Another functional load is working as an additional waterproofing barrier, together with the blind area;
Let's not forget about the aesthetic beauty of the building, which has a small distance between the ground and the walls, usually finished in contrasting materials in relation to the external façade of the walls.

How high should the foundation be above ground level?

This issue is very relevant, since most protective processes are not visible during operation, and all the benefits appear only in the long term. Based on this, many developers are trying to save on this design and exclude it from construction and estimate documentation.

However, many generations of builders and architects have repeatedly tested different options for constructing a country cottage, which has led, as a result, to the widespread use of above-ground basement distances in the construction of all houses. For each type of building material from which the cottage will be built, there are certain requirements about how high the foundation should be above ground level, which is necessarily taken into account by the designers.

The most common parameter is in the range from 30 to 50 centimeters - which optimally provides protection for a house built in central Russia. If the maximum level of snowfall reaches 20 centimeters, then the distance can be increased.

It is also worth considering the fact that about 10 centimeters of this height will be occupied by a blind area with surface finishing material - so you will have to increase the distance to the ground. Naturally, there are cases when 20 centimeters of height of the above-ground part of the foundation is enough - this is in those areas where the soils are not heaving and the maximum snowfall does not exceed 5 centimeters - in the south of our country.

We cannot ignore the fact that when constructing a country house, the height between the ground and the base of the walls is used to give the building originality and a unique style - for example, terraces are built below floor level with wide steps, or the platform can be built on stilts, which will give the house has charm and slight sophistication. The entrance block also has several steps with railings and a veranda, which also affects the image of your country residence. Perhaps the height of the above-ground part of the foundation is that rare case in architecture when purely functional details of a house could be turned into its highlight and an unusual decorative element. There are even cases when the base part is made protruding, in the form of an ancient “heap” - there are no restrictions on design and engineering ideas, as long as this part of the foundation regularly performs its main functions of protecting the house.

What is the optimal height of the foundation above the ground for the types of structures?

Based on the base material from which the supporting structure of the building will be created, the parameters of the distance from the zero mark are also selected. For example, the height of a shallow strip foundation is almost always equal to its underground part - that is, about 50-60 centimeters. However, there is no particular difference where strip foundation in the Moscow region will fit, since the approximate profile of the soil layer is the same for the entire central region and most surrounding areas of the country. By type of construction, you can provide approximate indicators for the distance from the edge of the wall to the zero ground level:

30-40 centimeters – for brick and monolithic structures;
40-50 centimeters – when using gas-foam blocks, large-sized ceramic materials;
Over 50 centimeters - when constructing a frame, prefabricated or wooden house, since the material is most susceptible to external influences.

How high should a monolithic foundation be made?

This question arises most often, since the strip foundation has a fairly small surface area of the foundation, which can be increased using various building materials. In the pile and screw version of the foundation, the technology itself provides for a minimum of 20 centimeters from the extreme point of the ground to the bottom of the grillage frame. Since a monolithic foundation slab, the price of which is already quite high, requires uniform pouring to a certain height, it is best to consult with the specialists of our company on how to simplify the design of the base and reduce the financial costs of creating a slab foundation. It is quite possible that the building design will allow you to create contour building of the base part using bricks, and filling the interior space with a more accessible floor screed. In any case, professional help will never hurt when creating a reliable and durable foundation.

Only a trained InnovaStroy specialist can determine exactly what foundation height will be sufficient for your specific cottage. More than 7 years of practice and our own experience in the field of suburban construction make it possible to provide each customer with objective and substantiated data on all the nuances of building a foundation for a cottage not only in Moscow, but throughout Russia. Use the services of professionals to prevent premature and unexpected costs for repairs and restoration of load-bearing parts of the cottage.

Before erecting any building, every serious builder will draw up a competent and detailed design of the structure, including the foundation. The project must indicate all the necessary parameters of the foundation: the width of the foundation itself (this applies, first of all, to the strip foundation), the area of its base, the depth, the material used during construction and the height of the foundation above the ground. All this must be taken into account at the design stage.

But knowledge cannot be used without understanding its essence, even if confirmed by the word of experienced builders. And in order to do any task correctly, it is necessary to understand the reasons for precisely such parameters and requirements. Here we are going to deal with the last parameter of the house foundation listed in the listing. What should be the height of the foundation and why is it necessary to know this? Why are certain numbers indicated in recommendations and projects? What experience do builders rely on?

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Difficult choice of ideal

It is believed that the price of the foundation in the total estimate for the construction of a house is about 30%. Therefore, if there is an opportunity to save money, then most will definitely do it. And in the parameters of the foundation there is an obvious point where costs can be greatly reduced - this is its height above the ground. The fact is that if the depth depends on objective and obvious reasons to everyone, changing something there, in terms of economy, is fraught, then the distance from the ground to the wall simply attracts the thrifty. After all, in fact, what is above the ground is the above-ground part of the building, and there is a temptation to make it all from cheaper materials. After all, every cm of foundation in terms of cost is much more expensive than the same cm of walls, especially if the latter are made of cheap materials (wooden, panel, etc. buildings).

But such savings are a mistake, and it is better for the owner of the future home to carefully read the requirements for this part of the foundation and understand why they are needed in order to take a balanced approach to the issue of the height of a strip or other foundation.

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The height of the base above the ground, what is its role?

Having carefully studied the role of the foundation of the house, you can see that it experiences various unfavorable factors. This is especially noticeable at the boundary between the soil and the atmosphere. From this it can be seen that the parameters of a conventional strip, block and other foundation include not only such functions as providing reliable support for the entire structure, insulating the house from harmful factors from the soil (primarily moisture), but also the function of raising walls and the residential level in general over all negative weather manifestations. Let's look at what this means point by point.

A highly erected foundation in its upper part can be well used as the base of a building. The benefit here is obvious; a solid structure will have better characteristics than in the case where the foundation and base are clearly separated. This will affect both the performance of the house and its integrity.
A high strip or block foundation has the best characteristics for protecting the walls of a house from moisture. Even if you use protection for the lower part of the walls (waterproofing, blind area, etc.), it will still be constantly moistened under the influence of ground moisture or precipitation. A high base in this case will protect the house from moisture much more reliably. The upper boundary of the foundation should rise 10 centimeters above the level of snow that falls in the snowiest winters. But in any case, the upper limit of the strip base should be no less than 30 cm above ground level.
The base, elevated above ground level, is sometimes part of the basements under the house, reflecting the design characteristics of the building. As in the case of the base, such a design of the house will have a good effect on its operation.
An elevation of 20-30 cm is also typical for pile and columnar foundations. There, this measure was taken as part of the fight against unstable soils. Heaving soils with this design have less impact on the structure during seasonal movements. In some cases, due to the slope of the terrain, this height above ground level can be much greater.
Very often it is a measure to combat the shrinkage of a structure. That is, taking into account the characteristics of the soil, builders add some additional height to the foundation in advance in anticipation of future subsidence of the house.
During construction, materials that are extremely unstable to high humidity and other environmental influences, such as wood, are often used. In this case, builders can also use a high base to prevent the wood from coming into contact with the wet soil.

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Calculation of the height of the strip foundation

Let's look at calculating the parameters of its height for an average house. The practice of the modern construction industry shows that the height of the above-ground part of the base of a house should be related to its width as one to four. We are talking about a classic shallow monolithic strip foundation, without basements and a plinth, with the inter-foundation space filled with soil. That is, the height of the part of the foundation above the ground should be 4 times the width. In this case, the above-ground part cannot be larger than the underground, and the opposite situation will be quite normal. In our area, both parts of the foundation, as a rule, have the same height and depth characteristics and are about 45-50 cm. If the house has an underground floor, then the foundation must have vents for proper ventilation of underground spaces.

The parameters determined when designing building structures include the height of the foundation, determined from the level of support on the underlying soil (fill cushion) to the upper plane on which the crown, floor slab or heel of the structure’s column rests. The value of the height of the foundation above ground level, which has its own selection criteria, is taken separately. Recommendations for drafting all types of supports, instructions on what requirements the foundation for a house must meet, are contained in SNiP 2.02.01-83* (2011 edition).

Criterias of choice

In the construction estimate, the height of the foundation will directly affect the cost of the work. Therefore, it is necessary to choose a reasonable balance between the minimum required rise above ground level and the desired size of the plinth, porch and associated structures.

The supporting area of the base largely depends on the weight of the building, while at the same time the level of the foundation above the ground determines the need for protection from environmental conditions (heat loss, preventing moisture from penetrating through the floors).

For each case, it will be necessary to perform a calculation in which the height of the strip-type foundation will significantly affect the total mass of the structure. But the height of the pile foundation above the ground (for example, for a bathhouse) can be chosen based more on the terrain, the height of the snow cover and ease of use.

The different needs for the MZLF insulation scheme, determined by how much their top elevation is above the ground, are shown in the diagram:

In cases where the base is not only a support, but also a space for technical, utility rooms, a cellar or a garage, a qualified design calculation must be made taking into account ventilation, waterproofing and insulation of all compartments located in the basement.

High altitude

The total height of the supports consists of 2 components: above-ground and underground parts. Typically, most of the part is located below the surface of the earth for stability. If the project includes a high base, its above-ground size cannot be more than ½ of the total value.

A limitation on the lower mark may be a high groundwater level. If the groundwater level on the site is lower than 2.5 m, then the foundation will allow you to immediately place a room with a height of 1.7 m to 1.9 m in its underground part, without a high base going above the ground. It is necessary to maintain a distance of 0.5 m to the level of the maximum seasonal rise of water in the soil. The beneficial use of the internal volume of the foundation structure significantly increases the scale of excavation work, since it is necessary to remove all the soil in the pit and go deep to the solid load-bearing rocks.

Do-it-yourself work when installing a buried foundation can be seen in this photo:

All requirements that a high foundation must meet are set out in SNiP 3.03.01-87, SNiP 3.04.01-87.

Minimum size

To ensure protection of the walls of the house from the effects of precipitation and soil moisture, heaving movement of the soil, it is necessary to create a gap between the crown of the house and the ground. It is precisely this goal that meets the height of the foundation above the ground, which is taken to be no less than 0.2 m for MZLF and columnar supports.

If the site has a slope, then this distance in different places can be greater.

The project, based on engineering and geological surveys, includes the possibility of how much the building can undergo subsequent shrinkage.

This approach is especially relevant for wooden buildings - log houses, bathhouses. In this situation, a sufficiently high base is usually provided on screw piles or bored-type columnar supports.

It is enough to install light temporary buildings on block pads to create an air gap between the ground and the bottom of the wooden structure, as in this photo:

For special-purpose buildings, the minimum height is determined by the installed communications and manholes for inspection and cleaning of the subfloor.

For example, raising a bathhouse above ground level makes it possible not only to break the connection with freezing soil and storm flows, but also to achieve natural drainage of used water through cracks in the floor.

The necessary ventilation and access to the underground for cleaning are provided with a pile foundation having a height of at least 0.5 m from the ground level.

Parameters that determine height

In the design calculation, the minimum height above the ground of the building's foundation is determined by a complex of factors present. You can display the required value for the selected type of base if you know the following parameters:

materials for construction;
soil characteristics;
presence of a basement;
snow depth;
groundwater levels, storm water levels;
freezing depth.

In practice, the minimum of 0.2 m is rarely observed; more often, a lifting height of 0.35 m - 0.4 m is prudently chosen. In cases where the building is erected on an area with clay soil, the height can reach 0.8 m -0.9 m On sandy soils, 0.5 m is usually sufficient.

The height of the slab foundation, depending on the total weight of the building, will be from 0.2 m to 0.4 m.

In a monolithic MZLF, vents are installed for ventilation, which have established standard dimensions, and this also affects the height of the above-ground part. Water should not flow into them and small rodents should not crawl into them, so they are located at a level of 20 cm and above.

The level location of such openings can be seen in this photo:

The easiest way to maintain the optimal height is to build the base on screw metal piles. It will not require a large amount of excavation work, costs for formwork and special construction equipment. The pile is screwed in manually. To strengthen the structure, concrete is poured inside.

Each pillar can have a different immersion depth when achieving reliable support on solid layers of rock. The height of the pipe remaining above ground level makes it possible to take into account the terrain and cut all elements into a single horizon after the entire pile field has been assembled.

The required rigidity is additionally ensured by tying with a grillage and, if necessary, scalding with bevels.

Add-ons

For a rough estimate, it is assumed that the cost of the foundation is about 30% of the total estimate for building a house. You can save on the consumption of materials for any type of foundation at the height of the structure above the ground.

The design calculation of a screw foundation for buildings consisting of light frames, log houses, prefabricated panels is not very difficult. Work is carried out at any time of the year, on sites of any terrain (except for rocky and rocky soils). When the site is densely built, without causing damage to nature in the forest or on the river bank, small holiday houses, bathhouses, gazebos, and fences are often placed on screw supports. Building a dacha on high pillars allows you to make good use of the space underneath (summer kitchen, car parking).

For monolithic solutions and brickwork, a standard of 10 cm in excess of the snow cover characteristic of a given climatic region is used.

How to determine in practice, using a water level, what the actual height difference of a monolithic strip foundation is, can be found in this video:

When marking and installing the support, it should be remembered that the height of the foundation at each point must be such that the upper plane has deviations from the horizontal surface no more than permissible values.

Construction Materials

Peter Kravets

Reading time: 3 minutes

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When building a house, the height of the basement is taken arbitrarily, based on the wishes of the owner, who decided to make a room in the basement for various purposes, for example, a kitchen with vegetable storage. But when calculating, they still use data on the type of soil, type of foundation and materials used.

There are times when, when building a basement, they do not pay due attention to it, sincerely believing that it is enough to just take it beyond the surface of the earth in order to continue building the house. But this assumption is fundamentally wrong.

It is necessary to understand that the base is the part of the house located above the ground. And the greater the height of the basement, the less moisture penetrates inside. Groundwater, floods, precipitation - there are a lot of sources of moisture impact on the foundation, and this process occurs constantly.

Foundation walls must be separated by layers of waterproofing from the main part of a two-story (or more) residential building, since moisture still penetrates through the smallest capillaries into the material and significantly increases the level of humidity in the premises.

If a kitchen is installed in the basement, it is necessary to insulate it from moisture from the inside, since steam from processing products will form condensation.

When constructing a basement, you can use SNIP 2.08.01 for residential buildings and SNIP 2.08.02 for public buildings.

If the walls of the building are placed too low, the bottoms of the structure will constantly get wet, which will lead to their slow destruction and loss of thermal insulation properties.

As a result, the period of use of the building will begin to decrease, and it will not always be clear due to what factors. This explains the importance of the plinth occupying the required height from the ground surface.

Typical parameters for the height of the plinth from the ground according to the rules

To find out what the maximum height of a technical underground can be, it is necessary to clarify the minimum parameters. According to the requirements of building codes, in a residential country house the minimum height of the plinth should be approximately 0.3-0.4 m.

When installing with a wooden beam, this distance should be increased to 0.6-0.8 m. If the presence of a ground floor is provided, then the minimum height of the technical underground will be from 1.5-2 m.

To determine the height in a particular case, the climatic conditions of the construction site, the likelihood of flooding with melt and groundwater, the frequency and abundance of precipitation, indoor and outdoor temperatures (especially in winter) are taken into account.

If possible, to take into account all these factors, it is better to seek help from professionals, although theoretically, these calculations can be carried out independently.

This issue touches on the risks of repair and re-equipment of the structure, as well as significant financial expenses.

In order to understand why the optimal height of the base of a house is calculated, it is necessary to determine several of its functions:

Preventing the interior of the house from getting wet;
Compensation for shrinkage phenomena of the soil that occurs when the weight of the house structure puts pressure on it;
Protection of building facing materials from contamination;
High-quality ventilation of underground spaces (when arranging kitchens, additional ventilation ducts are installed);
Increasing the service life of the floor when using a strip or columnar foundation; in addition, the thermal insulation performance of the subfloor depends on the height of the base;
Improving the appearance of the building, since a house with a basement visually looks very presentable.

It is necessary to pay special attention to the height of the base when building from wooden beams, which are susceptible to rotting at the ends of the logs, which significantly complicates repair and restoration work.

With this type of construction, they try to reduce the likelihood of wood rotting; for this, the height of the base above the ground is increased. Practice shows that some builders make a huge mistake by trying to reduce this height and neglecting the base for the sake of aesthetic considerations.

Among the disadvantages of increasing the height of the base, one can only name the increase in the cost of building a residential building.

Important! In order not to rely on the advice of builders and your own considerations, it is important to know the regulatory documents, which indicate the verified minimum height with an explanation of the origin of these verified values.

For example, SNIPs 31-02-2001 and 2.08.01-89 (height of the basement) establish a height of at least 0.2 m for columnar and pile foundations. Such an indentation is necessary on heaving soils to avoid their impact on the house. The greater the slope of the ground, the higher the ground floor should be.

Types of socles

The construction of a basement may differ in type and sequence of work depending on the type of foundation. Most often, strip or pile foundations are used. In some cases, the base of the house is poured with a monolithic layer.

When choosing a strip foundation, the basement can be monolithic (in the form of a concrete wall) or masonry (in this embodiment, the foundation is made to the level of the ground surface, and then the masonry is erected - it is not enough to protect against various influences, therefore it is necessary to carry out insulation work and decorative finishing).

In relation to the walls of the facade, the plinth can be designed as recessed (for buildings with thick walls), protruding (the only possible for buildings where the basement floor and thin walls (apartment buildings)), and flush (part of the plinth smoothly passes into the facade, all parts of the house are located in one plane, usually one-story houses or a summer kitchen in the country).

The influence of the type of base on its height from the ground according to standards

The most expensive, but necessary option, is the protruding type. It is only possible for buildings with a used basement. The maximum height is taken for this case, otherwise it is impossible to achieve acceptable thermal insulation characteristics of the building.

For buildings without basements or a basement (most often a summer kitchen on a personal plot), it is worth choosing a sinking option. The facade overhanging wall will be optimal protection against mechanical and atmospheric damage. In this case, the height is taken to a minimum; the lower it is, the better the protection will be.

The base of the house is on one of the low foundations, usually made of blocks or bricks. It should be noted that the use of blocks significantly increases the strength and stability characteristics of the building.

Both types of execution require finishing work and insulation work. If groundwater passes close to the surface, then a drainage system is installed, and if it is deep enough, it is enough to make a blind area.

The foundation on piles can be low (if the grillage is located at ground level) or raised. Columnar, as the most unstable, requires a height of at least 0.2 m.

The gaps between the pillars are filled with bricks or shields. Due to design features, there cannot be an excessively high base. The arrangement on stilts with different height options can be found in the freely available photo.

Features of waterproofing and insulation at different heights

But no matter how thoroughly the strip foundation is built, its effectiveness can be reduced to zero if ventilation openings are not installed along the entire perimeter at a distance of no more than 3 meters from each other. They provide high-quality ventilation, as do internal partitions and walls.

Cover such openings with ventilation grilles to protect against the entry of debris, dirt and small insects into the room. The use of plugs for these purposes is strictly prohibited, since the inherent moisture in basements can lead to mold and fungal manifestations.

If a kitchen is installed in the basement, then you should also take into account the steam from processed products. Examples of this use of underground can be found in many photographs in open sources.

Important! In a public building, technical basements should be divided for fire safety purposes, by partitions into compartments of no more than 500 m2, in non-sectional residential buildings, and in sectional ones - in sections.

In the distribution of costs for building a house, the foundation can take up to 30% - 40%, so if you want to save on this part, the minimum height of the base must still be observed, as a necessary condition for the long operation of the building. The elevation of the supporting structure above the ground surface performs a number of important functions, and it is provided for in all types of foundations. A properly made plinth performs its tasks regardless of whether it contains a basement, a cellar, or just pillars covered with siding for a light outbuilding.

Problems of the basement elevation

When building your own home yourself, you often pay less attention to the height of the base above ground level than to the depth of the foundation. It is not standardized as strictly and is not described in such detail in the GOST requirements.

In the foundation, this part, in addition to transmitting the load down to the support, performs 2 of its own tasks:

hydraulic fracturing between soil and walls;
underground ventilation.

The capillary rise of moisture through materials (concrete, brick, wood) is prevented by laying waterproofing along the upper plane of the base. The height to which the basement wall is raised protects against water falling on the outer surface of the building in the form of secondary drops, contacting snow cover, soil deposits and debris, as shown in this figure:

A clear answer to the question of why it is necessary to maintain the minimum required height of the plinth above the blind area near the walls of the house is shown by a practical example from a specialist in this video:

Insulation

Regardless of whether the house is one-story or has several tiers, wooden or brick, the base is combined into a single whole with the underground part of the foundation with a thermal insulation and waterproofing coating.

The lifting height above the ground is calculated taking into account the protection of the internal structures of the first floor floor, as shown in this drawing:

In this example, the base is raised above the zero mark by 0.6 m, since the thickness of the floor slab is 0.2 m. The second component of 0.4 m can be determined by the thickness of the snow cover characteristic of the area and the size of the vents, which are located 0.1 m above the snow.

To maintain the required height, monolithic strip foundations are often made in a combined (materials) version. To do this, the above-ground part of the tape with vents is laid out from red burnt brick, as in this photo:

At the same time, you should not unnecessarily build a high base (with a margin), since the cost of insulating the base increases. Depending on the type of design solution, heat loss from the surface of the protruding base reaches from 10% to 15%. In the case of a high, uninsulated base made of concrete, brick, or rubble stone, this value can increase up to 40%.

The influence of the blind area

In the design of a light or medium weight house, the base part is usually a continuation of the underground support made of the same material. The minimum height above the ground allowed by SNiP is 0.2 m. Support belts measuring 0.4 - 0.7 m work practically effectively. An insulated blind area around the perimeter of the building allows reducing material consumption by reducing the overall height of the foundation.

One of the parameters that determines the depth of foundation is the depth of soil freezing in a given climatic region. The indicator is given in the following reference table:

The overall height of the support (ribbon, pile, pole) in the project will be 0.5 m larger (standard requirement).

Accepting a smaller depth of support for the house allows the option of local insulation installed under a concrete blind area around the building.

With an appropriate thickness of insulation and the absence of basements in the construction project in most areas, in order to obtain a stable capital support for the cottage, you can limit yourself to pouring MZLF with manual digging of trenches and installation of low formwork, as in the following photo:

The concrete blind area protects against the penetration of water from the surface of the earth to the foundation materials, but it is necessary to provide effective protection from moisture flowing down the wall during rain to the base. It will depend on the selected type of interface between the wall and the base:

Speaker. The basement part of the foundation is wider than the walls and requires the additional installation of a canopy along the upper edge, which protects the surface located underneath from flowing precipitation. Another function of such a canopy is as a decorative decoration for the facade of a building.
Sunken. The most reliable option is when the junction of the outer wall and the base plane is made with a step. The stones come off the edge without wetting the foundation, which increases the safety of operating conditions for the base material in combination with the waterproofing coating. This type does not require the installation of bumpers for drains.
In the same plane as the wall. It is not popular, since it still requires the construction of a protective canopy that protrudes on the surface.

To understand the need for this measure (protection from water from the walls and draining it along the blind area into the drainage), you can calculate the average number of flowing liters in your area: average precipitation × wall area × 30%.

Useful plinth

If desired, you can arrange a cellar or a large basement in the underground space of the foundation, if the result of the survey of the engineering and geological characteristics of the construction site allows.

For specific construction conditions, you can calculate how to equip a useful room even for a private house standing on screw piles, a support in the form of a slab, flooded soils or flood rises of groundwater to a level less than 2 m from ground level.

SNiP 31-01-2003 of the Russian Federation considers a basement floor to be a room located below ground level at a depth not exceeding 1/2 of its height. The height of the above-ground part cannot exceed 2 m.

Structurally, the structure of such a foundation with a basement level differs little from conventional burial.

The base of the concrete slab is poured to the calculated depth and walls are erected on it. The strip base is made monolithic or from foundation blocks, its solid underground part evenly passes into the basement wall with windows and vents.

An example of installing a monolithic first floor on a slab is visible in the photo:

The characteristics of materials for such construction will depend on the characteristics of the soil and climate in a particular area. On dry, stable soils, you can take hollow blocks with low mass. Their main advantage is low thermal conductivity, which reduces heating costs when building a usable basement level.

To obtain useful premises for various needs without increasing the area allocated for the construction of a private house, a foundation with a technical room, cellar or garage, included in the terms of the assignment at the stage of drawing up the project, allows.

If the placement of useful rooms in the basement is provided before the start of construction work, then you can get a tangible effect from the investment. But when the building has already been commissioned and is in operation, the need to maintain the stability and load-bearing capacity of the finished foundation imposes significant restrictions on the possible layout of the basement space and technological operations for its equipment.