An extension to the house on a columnar foundation. How to make a foundation for an extension to a house. The procedure for erecting the foundation of the extension

The need to connect the old and new foundation arises when building an extension to an existing house: this is the easiest way to increase the usable area of \u200b\u200bthe house if you achieve a strong and reliable connection. For extensions, different types of bases can be used, and in all cases it is necessary to choose the right option for connecting the base. How to attach a new foundation to the old one, and what connection methods can be used during construction?

Difficulties in connecting the bases

There may be several answers to the question of how to properly attach the foundation, since the choice of specific solutions directly depends on the house itself. If you're going to build an extension on a building you've just built, the foundation bond will be different than when you're attaching an extension to an old house. Consider the main options for ligaments:

If the building was built a long time ago, it managed to go through all the stages of shrinkage and firmly took its place in the ground. In this case, it is most appropriate to connect an extension with a tape or slab base with a rigid hitch - a connection based on a common reinforcing cage.

It is created by drilling holes in concrete and reinforcing bars are inserted into them. This solution is not used as often as it is only suitable for non-rocky soils with high bearing capacity.

If the house has just been completed, and the shrinkage processes will continue for several more years, it will be necessary to build a new independent foundation with an expansion joint. It will allow you to connect the two parts of the building, but at the same time provide compensation for any impacts during shrinkage. The expansion joint also serves as a heat insulator, additionally closing the lower part of the house from the penetration of cold.

The second option is most often used on heaving soils, on which it is difficult to predict how shrinkage will take place and what effect it will have on the foundation of the house. To build an extension with an expansion joint means to protect it from cracks in the base, and it can last a very long time.

Rigid method of connecting foundations

If you have purchased an old house, it is advisable to ask the previous owners in as much detail as possible in advance about all the features and time of construction of the house. The most difficult thing is when the building was built a very long time ago, and during the service it managed to change several owners. It will be difficult to find information about when the foundation was overhauled and what type of foundation was used for this structure.

To check this, a trench is dug along the house, after which it is necessary to assess the depth of the foundation and determine its condition. If it is still strong enough, and it will not need repairs soon, you can start preparing for the construction of a new room. Drawings are being prepared indicating the dimensions of the new premises, the location of doors and windows, as well as other information.

To ensure a strong connection between the old foundation and the new one, you need to do the following:

The dried base will be completely monolithic and firmly connected to the old foundation of the house. Such an extension will receive reliable support, and any changes in its foundation will be reflected in the foundation of the house. A single foundation is a reliable, albeit rather time-consuming choice.

Connection of foundations using an expansion joint

How to attach a new foundation to an existing one, if the construction of the building has just ended, and the owners realized that one more room would be required. In this case, it will be necessary to construct a new base with an expansion joint. The buildings will also be connected to each other, but if the shrinkage is uneven, it will not affect the foundation of either the main house or the extension to it.

The construction practice is very similar, but there is one very important difference. You can not use the connection with reinforcement, the only option is how to attach the foundation to the existing base - to prepare an expansion joint.

It is an ordinary board, the thickness of which is 2-5 cm. It is wrapped with roofing felt, polyethylene or other moisture-resistant material, after which it is placed in the space between the old and new base.

The new foundation is poured with concrete on the reinforcing cage, the construction is practically the same as the first option. However, after the concrete has hardened, the expansion joint is removed, and the space is filled with insulation and mounting foam. These are relatively elastic materials, therefore, during ground vibrations and during shrinkage, they will not allow cracks to appear in the foundations of the building and extensions to it.

This is a very simple solution that will solve many problems. The expansion joint reduces the risk of damage to the foundation as a result of ground movements, and the building with an extension can last much longer. Such a seam is necessary: if you do not take care of it, in a few years the building will need a major overhaul with the dismantling of the floors.

The construction of foundations is most often carried out in the autumn. At the very end of the construction season, you can pour the base of the house, after which it will shrink within six months, and after that it will be possible to safely proceed to further construction.

Construction of a column foundation for an extension

How to attach the foundation to the old foundation, if it is planned to erect a simple frame extension? This is a fairly simple solution, since frame structures are very inexpensive and are built quickly, and because of their low weight, a lightweight foundation is enough for them. Usually, monolithic reinforced concrete columns or metal screw piles are used for this, which are also relatively inexpensive.

It will not be difficult to install a light frame structure. First of all, the dimensions of the extension and the number of pillars that will be required to support the weight of the extension are calculated. Usually they are located at a distance of 1-1.5 meters from each other, in addition, they must be placed in the corners and in all places that will be under increased load.

Concrete columns can be made from asbestos-cement pipes, which are dug into the ground at a level below the freezing of the soil, or ordinary concrete blocks can be used. Asbestos pipes will serve, in this case, as a fixed formwork.

Another option is brick columns, it will not be difficult to build masonry, and it will be very durable. A shallow foundation is used only for the lightest structures, and if you want to build an extension from logs or other durable materials, it is better to build a strip or slab foundation for them.

Waterproofing is laid on the pillars, after which the lower frame trim can be placed on them and construction can continue. At the junction of the walls of the extension and the house itself, an expansion joint is also provided from waterproofed boards or other materials, and subsequently this place is firmly insulated and covered with mounting foam.

The advantages of a columnar base are many:

It builds quickly. Putting a few concrete posts can be much faster than pouring a strip base, and then waiting for many days for the concrete to dry completely. The columns can not be poured: if a small frame extension is being built, ordinary concrete blocks will suffice.
You don't need to enlist the help of other people. You can install the columns gradually, it will not be so difficult to cope with this work alone. But there is also a minus: in order for the pillars to remain at the same level, you should not delay the construction too much after they are installed.
This is an inexpensive solution. Little building materials will be required, in addition, sometimes the base of the extension can be built from what is left on the site after the main construction.

Strip foundation for a wooden extension

Timber and logs are the most common materials for the construction of light extensions: they are affordable, help create comfort in a living space, and besides, they are the most environmentally friendly materials. For outbuildings from these materials, a strip base is most often chosen, made with an expansion joint or a rigid screed. Such a structure is a reinforced concrete tape, which is poured on a pillow of sand and gravel.

The strip foundation is easiest to connect to an existing foundation; both the rigid connection method and the expansion joint can be used. But there is another solution: if you are building a house yourself, you can foresee the location of the extension in it and add it to the project. In this case, the foundation for it can be prepared immediately, and after the completion of its shrinkage, it remains only to implement the rest of the project.

The tape base is built quickly, it is built as follows:

The site for the extension must be prepared for construction: it must be leveled and cleaned of construction debris. After marking the territory, a trench is prepared to the depth of the main foundation.
Formwork is installed along the edges of the new tape, and a reinforcing cage is laid along the bottom. Much depends on the correct reinforcement, since it has to withstand the weight of the building.
The solution is poured along the entire length of the new foundation. It is desirable to completely fill the tape base at a time, otherwise it will not be so strong. After that, it should dry completely.

The finished tape base of the extension is covered with multi-layer waterproofing: roofing material and bituminous mastic can be used for this purpose. Protecting walls from moisture is necessary regardless of the materials of construction, since any walls will gradually collapse if they are exposed to extreme conditions.

The design of the house made it possible to do so, but I nevertheless advised that the foundation for the extension to the house be made simultaneously with the foundation of the first stage of the house and, having laid the flooring on it, use it for the time being as a recreation area. In this case, during the construction of the extension, there are no problems with the base, foundations and joining of the walls.

Another, more complicated situation arises if there is a need for a new room when the house is already fully built.

Foundation for an extension to the house must meet the requirements of reliability. Since it closely interacts with both the common base and the foundation of the house, when choosing a foundation and its design, and calculating the parameters, you must have the following information:

what foundation for an extension to the house is used under the existing house, what is its design, level of laying, the width of the sole of the strip foundation or the pitch and area of the columnar supports;
what are the soil conditions of the construction site, including: the type of soils, their physical and mechanical characteristics, the calculated resistance of soils at the base of the house, the heaving properties of soils within the depth of their freezing.

There are two possible situations when solving the questions posed:

project documentation for the house and foundations is at the disposal of the developer and, therefore, the designer;
the documentation was not preserved or it did not even exist. As one developer said, “all the decisions were in the head of the foreman, but we had to part with him.” Often, documentation is also missing when buying a finished home.

It is clear that in the second situation, the amount of work that needs to be done when developing the extension foundation will be much larger.

In such cases it is necessary:

near the house at the junction of the extension, dig a pit to the depth of the foundation;
determine the design of the foundation, as well as the presence or absence of a sand cushion;
determine the dimensions of the supporting part of the foundation of the house;
in the process of digging a pit and subsequent drilling of a well, take samples for laboratory determination of the physical and mechanical characteristics of soils, their calculated resistance at the level of the base of the foundation and the degree of heaving of the base.

The width of the sole of the strip foundation can be determined as follows. A steel rod with a hook bent at the end is hammered under the sole with the hook horizontal. After that, the rod is turned, setting the hook in a vertical position, and pulling it all the way into the foundation for an extension to the house. Then they make a mark on the rod and, turning the hook to a horizontal position, pull it out from under the foundation, after which the marked part of the rod is measured.

Having the specified data, it is possible to make a decision on the design of the base and foundations of the extension and the way they are paired with the foundation of the house.

Unlike the foundation of a house, decisions on which are made for reasons of reliability, economy and manufacturability, decisions on the foundation of an extension are also made depending on the design of the existing foundation.

In addition, the following conditions must be observed:

since different foundation designs interact with heaving soils in different ways, one should strive to apply the same design under the foundation for an extension to the house as under the house, if the latter meets the reliability requirements;
it is necessary to avoid laying the foundation of the extension below the foundation of the house;
by calculation and constructive measures, it is necessary to strive to ensure the deformation of the sediment and heaving of the foundation of the extension at the same level as that of the foundation of the house;
the foundation for an extension to the extension house during the manufacturing process and its subsequent operation should not cause additional settlement of the foundation of the house that exceeds the allowable values.

Reliability of the foundation for an extension to the house

Since the requirements for the reliability of the foundation for an extension to the house apply to the same extent to the reliability of the foundation of the house, let us dwell on the content of this concept in more detail. In different soils and at different depths of the foundation, the scope of the content of the concept of "reliability of foundations" varies significantly.

The reliability of the foundation in non-rocky soils, when its deepening is taken constructively and does not depend on the estimated freezing depth, is considered to be ensured if the dimensions of the supporting part of the columnar or strip foundation are determined depending on the loads from the house and the calculated soil resistance at the depth of its laying. In such soils, only foundation settlements are possible, which, if the specified condition is met, will be within the limits allowed by the Norms.

Practically non-rocky soils include coarse-grained soils, gravelly, coarse and medium-sized sands. In such soils, slight precipitation, as a rule, quickly stops after the construction of the house is completed.

The reliability of the foundation laid in heaving soils below the estimated freezing depth is considered to be ensured only if:

the dimensions of its supporting part are determined taking into account the loads from the house and the calculated resistance of the soil underlying the base of the foundation;
heaving deformations of the foundation under the action of tangential forces when the soil freezes to the calculated depth are equal to zero and, therefore, the foundation is stable.

For a deep foundation in heaving soils, only sediment deformations are allowed.

The reliability of a shallow foundation used in heaving soil is considered to be ensured under three conditions:

the dimensions of the supporting part are determined taking into account the loads from the house and the calculated resistance of the compacted sand cushion or the soil underlying it;
when heaving soil freezes to the depth of the foundation, the heaving deformations under the action of tangential forces are equal to zero, that is, the foundation for an extension to the house is stable;
when heaving soil freezes below the base of the foundation to the calculated depth, the heaving deformations do not exceed the values \u200b\u200ballowed by the Standards, which are taken in the same order as the sediment deformations.

Node 1

For such a foundation, both sediment deformations and heaving deformations are allowed, but the foundation must be stable - the separation of the sole from the base by tangential heaving forces is not allowed. Heaving deformations are limited by the device under the foundation of an anti-heaving cushion made of compacted non-heaving soil - coarse or medium-sized sand.

It is also necessary to determine the reliability of the foundation arranged under the house, which can be visually assessed by the presence or absence of cracks in the basement, in the brick or block masonry of the walls, as well as distortions of the box of a wooden house, veranda, porch.

If there is a project for the house and the results of the survey, or if the necessary information is obtained by measuring the structures of the house to which the extension will be adjacent, digging a pit and drilling a well, you can perform a more detailed check of the foundation of the house. Namely: calculate the loads from the house, determine the required width of the supporting parts of the strip foundation or the area of the pillar foundation supports, check its stability under the action of tangential heaving forces, determine the magnitude of possible heaving deformations.

The results obtained are taken into account when calculating the parameters of the base and foundation of the extension. When making a decision on the design of the foundation interface, it is possible to predict the difference in the expected movements of the structures, which must be taken into account, for example, when installing floors at the entrance to the extension,

Constructive solutions for adjoining the foundation for an extension to the house

On fig. 1 schematically shows some options for adjoining the foundation of an extension to the foundation of a house according to the scheme of open and closed circuits.

Rice. 1. Options for adjoining the foundations of the extension according to the scheme of open (a, b, c, d) and closed (e) contours: 1 - existing house; 2 - extension.

There are two options for arranging the junction of the foundation of the extension with the foundation of the house: by rigidly connecting them with reinforcement or by placing an expansion joint between them. And the ways of connecting the walls of the extension with the walls of the house are completely dependent on these options for pairing the foundations.

Expansion joints are widely used in industrial and multi-storey residential construction, when, for example, soils with significantly different deformation characteristics lie under an extended structure in its different parts and, under the same loads, different amounts of precipitation are possible. These seams are also used when extended structures in different parts have different number of storeys and, therefore, give different loads. This can result in different sediment deformations.

I use expansion joints and also when another structure is attached close to an existing structure.

In these cases, expansion joints are provided immediately at the design stage.

In low-rise housing construction these options, except for townhouses, do not take place, since we are talking only about an extension that is functionally connected with an existing house. Therefore, when developing the foundation of an extension, first of all, there is a desire to rigidly connect the foundations.

In the case of adjoining an extension according to the scheme on rice. 1 and this can be done by drilling holes in the foundation of the house with a diameter equal to the diameter of the reinforcement to a depth of about 35 of its diameters, and hammering reinforcement into them with an outlet of the same length. For fittings ø14 mm, the outlet depth will be 0.5 m.

When adjoining an extension according to the scheme on rice. 1b when the width of the foundation under the house is less than 35 diameters of the reinforcement ( pic 2 node 1), holes in the foundation of the house are drilled to a part of the width, and the reinforcement is driven in like an anchor - with a longitudinal slot at the end, into which a wedging insert is inserted before driving ( pic 2 node 2).

Rice. 2. Rigid options - connecting the foundation of the extension with the foundation of the house: a, b - with an open contour of the foundations of the extension; in - with a closed circuit; 1 - fittings.

When building an extension foundation according to a closed loop scheme ( rice 1d) holes are drilled in two levels in a checkerboard pattern with anchor wedging of reinforcement, at the other end of which a washer is welded ( pic 2 node 3).

The number, pitch and diameter of reinforcement are determined by calculation from the condition of its least resistance to shear or crushing of concrete under it.

The need for a rigid connection of the foundations first of all arises when the extension project provides for its construction under the same roof with the house (Fig. 3a,b,c).

However, a hard connection device is possible, for example, and when the recessed strip foundations of the house and extensions are made of monolithic reinforced concrete, and when using a shallow foundation, the plinth forms a single monolithic structure with the foundation,

With prefabricated strip foundations and plinths, it is impossible to ensure their reliable connection. And when using columnar foundations, a rigid connection is possible when the height of a single monolithic grillage - the base is sufficient to accommodate anchors.

When using a slab foundation under the house a rigid joint is possible if the slab on the side of the adjoining extension has a sufficient protrusion from the base, not less than the thickness of the slab. In this case, it is possible to remove the protective layer of concrete, expose the reinforcing cage, weld or tie the reinforcement cage of the extension to it.

To a house with a basement or those underground a rigid connection of a basement-free extension on a shallow reinforced concrete strip foundation can be provided if the recessed walls and the basement of the house are made in a monolithic version.

A rigid connection of foundations is advisable if the following is established on the basis of an examination and calculations:

the foundation of the house is securely arranged, and the foundation for the extension to the house is calculated in accordance with the requirements of the current Norms and on the basis of the engineering and geological surveys performed;
by the time the extension was erected, the house had already settled and it was established by calculation that the foundation for the extension to the house during precipitation, if it hangs on the foundation of the house, will not cause the latter to settle more than the permissible values.

More reliably, it is possible to provide a rigid joint of foundations in non-rocky soils.

As can be seen from the above, to ensure a reliable rigid connection of foundations in heaving soils, it is necessary to solve a rather complex engineering problem with many preconditions and limitations.

Technologically, the task is also not easy.

Rice. 3. Options for building an extension: a, b, c - under one roof with a house; r, d - with an independent roof.

In many cases, it will be easier and more economical to build an extension using an expansion joint, when, for example, a one-story building under an independent roof is attached to a two-story house ( rice 3 d, d) or when a prefabricated foundation is used under the house in heaving soils or the foundations under the house and the extension differ structurally.

When using an expansion joint, the gap between the walls and the basement ceilings is filled with insulation, which should not cling to the structures. From time immemorial, such material as tow has proven itself well. The contact point is enclosed with a decorative overlay, which is attached to only one side, as a rule, to the wall of the house.

In heaving soils with an expansion joint, the floor level in the extension is arranged below the floor in the house by the amount of expected deformations.

The use of an expansion joint does not exclude the need to calculate the extension foundation in accordance with the reliability requirements.

Photo. The simplistic approach to building the foundations of the extension turned into a ruined house and a waste of money.

The practice of building extensions shows that a simplified approach that ignores the requirements for ensuring both the reliability of the foundation and other specified conditions often turns into trouble ( see photo) - useless spending of funds, the need to finish or remake the foundation of the extension, and even the need to carry out additional work to strengthen the foundation of the house.

For example, improper work when excavating trenches for the foundation of an extension next to a loaded foundation of a house can lead to significant additional uneven settlement of both structures.

Error correction

Information about the unsuccessful construction of extensions is received quite regularly. For example, one developer reported that he added a veranda on columnar foundations of asbestos-cement pipes to a log cabin erected on a strip foundation.

After the first relatively warm winter season, the veranda was severely warped. Only after that did he understand what heaving soil was and asked how it was necessary to arrange the foundation and could it be corrected? In his case, it was necessary to dig out some columns, besiege, lay insulation from extruded polystyrene foam under the veranda and around it, as well as arrange a blind area and storm trays.

Another developer added a cold garage made of the same blocks to a house regularly heated in winter with plastered walls made of foam concrete blocks. In places where the walls of the garage adjoin the wall of the house, reinforcement bars were arranged along the entire height for a rigid joint of the walls. But numerous cracks appeared on the plaster of the walls of the house and the garage at the junction by the end of winter. The situation also had to be corrected with the help of a heater laid inside and around the garage under the floor and blind area.

In construction practice, there were cases when, in heaving soils, the foundations of the porches, designed as a single frame structure with the external and internal foundations of houses, were performed by inexperienced builders secondarily as an independent structure. At the end of the construction, it turned out that in the second half of winter and in the spring it was impossible to enter the houses, since the platforms of the porches were heaving higher than the bottom of the entrance doors. In such cases, it was necessary to redo the foundations of the porches or apply insulation to prevent freezing of the heaving soil.

An example of a practical solution for an extension foundation

1. Initial data

1.1 It was required to build a two-story extension to a two-story basement-free residential building for permanent residence Fig. 4

Rice. 4. Plan of the foundation of the extension

1.2 The outer walls of the house are made of foam concrete blocks with chipped stone facing. The total thickness of the outer walls is 600 mm.

The height of the rooms on the 1st and 2nd floors is 2.7 m, the total height of the walls at the junction of the extension is 6.12 m.

The basement and interfloor ceilings are made of hollow reinforced concrete panels. Roofing with metal tiles is made on wooden rafters.

The basement with a height of 0.5 m from the ground surface is made of prefabricated small-piece blocks laid with cement mortar dressing. In some places, small cracks are observed in the seams of the block masonry of the basement and walls.

1.3 Documentation on the pound conditions of the construction site and the design of the foundations of the house was missing. The project of the above-foundation part of the house and the extension was provided.

It was required to make an extension of the same foam concrete blocks with a stone cladding. The basement and interfloor ceilings were provided from monolithic reinforced concrete. Work on the manufacture of foundations, the construction of walls, ceilings and roofs should be carried out without interfering with permanent residence in the house.

1.4 Near the basement of the house in the place of the extension, a pit was dug to the depth of the foundation. In the course of excavation and subsequent drilling of a well at a distance of 1.0 m from the house, soil samples were taken for subsequent determination in laboratory conditions of their physical and mechanical characteristics.

1.5 As a result of the survey, it was found that strip foundations were arranged under the house, deepened from the soil surface by 0.9 m. Rectangular foundations with a sole width of 0.6 m were made in a combined version. The lower part with a thickness of 0.35 m is represented by a monolithic reinforced concrete strip, the upper part is made of the same blocks as the plinth and is built with cement mortar dressing.

1.6 The construction site is formed by hard-plastic clays. Groundwater occurs at considerable depths. According to the degree of frost hazard, the soils are characterized as weakly heaving.
A compacted sand cushion 0.2 m thick was laid under the foundations. The backfill was made with local soil.

1.7 The normative depth of freezing in the Moscow region is 1.4 m. Inside the building patch of a house heated in winter, the soil does not freeze through. The calculated depth of soil freezing along the outer perimeter with floors arranged along the basement floor is 1.1 m (Table 1, SNiP 2.02.01-83 * "Foundations of buildings and structures"). Clayey potentially heaving soil under the foundation lies below the estimated freezing depth.

1.8 The predicted value of heaving of a snow-free surface of weakly heaving soil is -5.0 cm.
The specific tangential heaving forces that can act on the side surface from the outside of the foundation can reach 7.0 tf / m2 (Table 6.10, SP 50-101-2004 "Design and installation of foundations and foundations of buildings and structures").

19. Permissible values of deformation of sediment and heaving for houses with walls made of masonry materials without masonry reinforcement are equal: absolute deformations - 2.5 cm; relative deformations - 0.0005.

Making decisions on the foundation, foundation and technology of work

2.1 Due to the fact that the basement and interfloor reinforced concrete floors, provided for in the monolithic version, must be supported along the entire contour of the extension and, according to the condition of clause 1.3, cannot be supported on the walls of the house, the foundation is the basement and the walls of the extension are erected along the entire perimeter.

2.2. To determine the parameters of the base and foundation of the extension, it is necessary to determine the nature of the interaction of the foundation of the house with heaving soil. For this, the loads from the house to the base were calculated. On rice. 5a diagrams of linear loads on the base at the junction of the extension are presented. The calculated resistance of a compacted sand cushion at a depth of 0.9 m - from the soil surface and clay soil under it - at a depth of 1.1 m was determined.

Rice. Fig. 5. Diagrams of the maximum linear load windows of the base (tf / m) under the house (a) and under the extension (b).

According to the least design resistance of the sand cushion and the loads from the house, the required width of the parts of the strip foundation was determined, and the calculation of its design for stability under the action of heaving tangential forces was performed.

The calculations showed that with the accepted width of the supporting part of the strip foundation of 0.6 m, the pressure on the soil does not exceed its design resistance. Therefore, the precipitation that has occurred is within acceptable limits.

Calculations showed that the foundation is stable even when backfilled with local soil. The absolute deformations of heaving are equal to zero, but the rigidity of the cross-section of the foundation-socle, consisting of a reinforced concrete strip 0.35 m high and block masonry 1.05 m high, is not enough. Hence the observed cracks in the block masonry.

The linear loads from the structures of the extension to the base are calculated (Fig. 5b). And on the basis of the results obtained, it was decided to construct a strip foundation for an extension made of monolithic reinforced concrete for the entire height of the foundation - a plinth with a width of the supporting part along the axis 1 -0.4 m, and along the remaining axes -0.6 m.

Since a rigid connection with reinforcement to the block part of the foundation of the house is impossible, the foundation of the extension is built through an expansion joint, On fig. 6 the constructions of the base and foundations of the extension are presented.

Rice. 6. The construction of the base and foundations of the extension according to sections Ⅰ - Ⅰ and Ⅱ - Ⅱ (see Fig. 4):
1 - foundation-basement under the house; 2 - monolithic strip foundation;
3- foundation of the extension; 4- leveling pad; 5 - backfill;
6 - waterproofing; 7- prefabricated basement slab in the house; 8 - monolithic
basement slab of the extension; 9 - vertical layout under the blind area.

2.3 It is not possible to develop trenches for the foundation of the extension to the depth of the trenches under the built house due to the danger of disturbing the sandy base under the loaded foundations. Therefore, it was decided to dig trenches for the foundation of the extension only to the level of the sole of the foundation of the house.

The width of the trenches along the outer perimeter of the extension is determined to be 1.0 m, and along the part of the perimeter adjacent to the house - 0.8 m from the condition of stability of the foundation when filling the sinuses with coarse or medium-sized sand. Along the bottom of the trenches, after compacting loosened areas of clay soil, a leveling sand and gravel pad 50 mm thick was arranged with compaction, in which sand -40%, gravel -60%. It has been established by calculation that with the assumed thickness of the cushion and backfilling of the sinuses with non-heaving soil in weakly heaving soils, the heaving deformations of the extension foundation in this case are equal to zero.

2.4 So that the cement milk does not go into the sand during concreting, a waterproofing material was spread on the arranged pillow. After that, reinforcement, formwork were installed and concreting began. rice. 7 shows the reinforcement of the foundation - the basement of the extension.

Rice. 7. Reinforcement of the foundation of the extension along sections 1 - 1 and 2 - 2 (see Fig. 4)

The foundation of the extension is separated from the foundation of the house by an expansion joint, which is minimized due to the fairly even surface of the latter. The foundation of the house at the points of contact with the foundation being made serves as the second side of the formwork. The seam is formed by a roofing material attached to the foundation of the house.

2.5 When digging trenches at the junction of the extension immediately for the entire length of the foundation, there is a danger of the formation of unacceptable sediment at home, since its foundation is designed subject to its deepening by 0.9 m. pic 8.

2.6 In the production of foundation work, it was necessary to monitor the state of the structures of the house. To do this, alabaster marks were installed on the existing cracks in the places of the extension. In the event of cracks on them, it was necessary to suspend work and reduce the length of the stops.

2.7 After the extension is erected, it is necessary to arrange a vertical layout around it, a blind area and storm trays, which together make up a surface drainage system. The blind area in heaving soils was recommended to be made in separate blocks 1.5.., 2.0 m long and reinforced with a road mesh. The width of the blind area should overlap the sinuses of the backfill.

Rice. 8. Making the foundation with stoppers: 1 - releases of reinforcement; 2 - shuttering diaphragm-limiter; 3 - deformation seam.

In terms of importance and order of manufacture, surface drainage is in second place after the roof. But if the roof is not yet ready for the autumn-winter period, then it is still necessary to perform temporary planning and blind area, laying, for example, roofing material with a slope from the extension.

Is it true that the foundation for the extension differs from the main one, what are its features? Many people are looking for the answer to this question, because when adding additional rooms to an existing house, you want these rooms to also have a reliable foundation. We have collected the most important tips and instructions in this article.

Everyone knows what role the skeleton plays in the human body, similar functions are assigned to the foundation. In fact, this is the basis that is responsible for the reliability and durability of the building. Also, it is the foundation that provides heat and dryness in the room. If the base is of poor quality or does not fit the specific conditions, then dampness will appear inside, the floors may deform and even deteriorate. It also levels the ground level and prevents the penetration of carcinogenic gas from the soil into the dwelling.

Extension base

The choice of foundation should be treated with particular care. After all, it is necessary that it freely withstand the load and correspond to the type of soil. At the same time, there is no need to overdo it, for example, if you can fill in a tape or, then there is no point in replacing these simpler options with a complex monolithic base. Firstly, it is too expensive and will not justify the investment. Secondly, the first ones are much easier to perform and you can do them yourself even without outside help, but you won’t be able to lay a concrete slab on your own.

It is mainly built of stone or concrete, but there are also wooden structures. If the building is lightweight, then you can give preference to a shallow base located above the freezing point. But most often its depth should be below this level. According to its purpose, it is divided into carrier and combined. The latter, in addition to standard load-bearing functions, must also provide seismic protection. There is also a special type, it includes "swinging" and "floating" foundations, their pressure corresponds to the pressure of the excavated soil.

In this paragraph, we will consider what types the foundation for an extension is divided into. Tape can rightfully be called universal, because it is perfect for both heavy and lightweight structures. It is located only under the outer and outer load-bearing walls. It is mainly poured from concrete; to make the structure more reliable, it should be reinforced with iron rods. If you are going to make this type of foundation with your own hands, then it is better to give preference to the prefabricated version. The disadvantages include high cost.

Universal strip foundation

But columnar, on the contrary, refers to budget options. But it is advisable to use it only when it comes to lightweight structures, for example, you need to tie a frame extension to a wooden house. The supports are special pillars located at intervals of 1.5 to 3 meters. These pillars must be placed at the intersection of load-bearing walls. It is best to make such elements from brick or reinforced concrete, but larch bars can also be used. However, such supports are expensive, and wood is not durable.

If you are going to build a fairly massive building, while weak soil prevails, then you should give preference to the pile type of foundation. This design consists of supports connected by means of a strapping beam.

The foundation for the extension can be rigidly adjacent to the base of the housing, as a result of which a single structure is formed. Such a decision is relevant if the site has a weakly or non-heaving type of soil. It is also worth giving preference to this option when you are going to make an extension of several floors and want to connect it to the main housing through one roof.

If the base is a slab, then a monolithic foundation should also be poured for additional housing. At the same time, it is necessary that its thickness be at least 400 mm or the base of the residential building should have protrusions. In this case, it is possible to weld the reinforcement of the slab to the frame of the new foundation. In addition, if you wish, you can do everything with your own hands.

Monolithic foundation slab

The "tape-to-tape" connection assumes the presence of a sand cushion and reinforcement with a longitudinal slot. Metal rods are driven into specially prepared holes in the base of the house and form a frame for a new foundation. Next, the joint is made by means of a release about 40 cm long.

You can also build a separate base for an extension, which will be in close proximity to the house. A sheet of roofing material should be placed between the two bases. This material acts as an excellent waterproofing, you can also place a layer of thermal insulation or get by with a simple tow. In this case, it is very important that this layer allows the new base to not collect water during rainfall and not damage the foundation of the house. From the outside, special decorative overlays are fixed to the wall, covering the seam.

Now let's move on to the practical part and consider how to make a foundation for an extension with your own hands. This detailed instruction will help save on the services of a master, because it is designed for independent construction work.

Building a foundation for an extension with your own hands

How to make a foundation for an extension to a house - step by step diagram

Step 1: Choosing a base

The new foundation must fully comply with the type of the old foundation. In addition, the load and type of soil are taken into account. For example, if we are talking about a massive extension to a brick house, then it is necessary to lay a tape or make a pile foundation. But if the additional room is adjacent to the wooden housing, then it is possible to get by with a cheaper columnar option.

Step 2: Calculations

Regardless of whether you prefer a rigid type of connection or a separate foundation, the depth and width, as well as the dimensions of the foundation pillars, if any, should be the same as that of the foundation of the house. Determining these parameters is quite simple. It is necessary to dig a hole next to the housing wall and measure the dimensions of the base. If there should be no questions about how to measure the depth of the structure, then in order to measure the width, you should take a rod, bend one of its edges by 90 ° and put it in a horizontal position under the foundation. Then we turn the rod until its bent part rests on the back side. After that, you need to make a mark on the bar and pull it out. By measuring the distance from the hook to the mark, we find out the width.

Step 3: Preparatory work

Before pouring the foundation for the extension, it is necessary to carry out preparatory work. If you decide to give preference to a rigid connection, then we dig a trench of a given size and drill holes in the existing base. Moreover, their diameter must exceed the thickness of the reinforcement. Metal rods should also be prepared. It is necessary to make a longitudinal slot on their end and insert a special wedging insert into it.

Step 6: Pouring Mortar

We prepare a mixture of cement, sand, gravel and water. It is very important to keep the proportions right. For example, for the M300, you can take 10 kg of cement, 30 kg of sand, 40 kg of gravel, mix everything well and pour 40 liters of water. If the concrete is too dense, then you should dilute it with a liquid, but only add it in small parts so as not to spoil the solution. We pour concrete into the formwork and wait a few days until it completely hardens. We moisten periodically, otherwise cracks may appear.

Step 7: Forming the Column Foundation

Making such a foundation is relevant when a lightweight extension adjoins a wooden house. We drill wells so that they are below the freezing level of the soil. We form a sand cushion and install fiberglass reinforcement. This material has excellent properties and does not require additional treatment with waterproofing compounds. Formwork of specified dimensions is also formed and poured with concrete. This foundation for an extension is the easiest to perform, and everyone can create it with their own hands.

Step 8: Building a Separate Foundation

But when the number of storeys of the main and adjacent housing is different, then a separate foundation should be made in close proximity to the former one. The distance between the two bases is from 2 to 5 cm, depending on the number of storeys of the new premises. The higher it is, the wider the seam is selected. We fill this gap with thermal insulation materials or tow. Then a special decorative overlay is attached to the wall of the housing. In this case, it is very important to correctly mark the base. To do this, we stretch the cord on the pegs around the perimeter of the future site and check if the diagonals are equal. If the heaving type of soil prevails on the site, then the floor of the extension must be made so that it is not lower than the flooring of the main housing by the amount of possible deformations.

If you came to us, it means that you are interested in how to make a foundation for an extension to the house.

And this is not surprising, because most of the residents of country houses and cottage owners sooner or later think about expanding the area of \u200b\u200byour house, and with their own hands.

Someone is tired of living in a small room, where it is difficult to turn around, place anything and invite guests.

Someone wants to make a veranda or attach a room to the house that would serve as a summer kitchen.

Everyone has different reasons, but the problem immediately arises for everyone the same - where and how to start. With this, we will try to figure it out in our article.

Foundation types

You can’t even put up a good gazebo without a foundation, especially if the climatic conditions and the area in which your house is located are often flooded and rainy.

Many factors can destroy your extension if it does not have a foundation. So let's figure out together how to do it yourself.

And immediately we say that the foundation for an extension can be of three types: tape (lay out of brick, stone blocks or very rarely - from foam blocks), columnar or pile.

Each of them has its purpose, its advantages and disadvantages. But, as a rule, the foundation for an extension to the house is made according to the first or second principle.

The third is practically not used.

It is well suited for small buildings, such as gazebos or verandas, or small foam block buildings (it is a lightweight material, so it is quite possible to put it on a pile foundation).

In some cases, such a foundation will also fit a wooden house.

But for large objects, such as an extension to a house, a strong and reliable foundation is needed, which are its first two types.

Some recommendations for building a foundation for an extension

Think about the type of foundation your home has.

The problem is that different foundations interact with the soil in different ways, affect its shrinkage in different ways.

Therefore, if your house has a serious tape reinforced concrete base, and you make an extension to it from a columnar one, then sooner or later you will definitely lose your extension. It's better not to save here.

There is another problem that should be taken care of in advance. You need to decide if you want to tie the new structure to the foundation of the main house or do it separately.

And here, too, the leading role is played by how good the soil on which your house is built, how it behaves.

If you see that over time your house has slightly settled and the ground has remained the same uniform, then you can safely connect the foundations of the house and the extension. And it will be right.

But if the soil on your site and around the house sags, the house sinks or leans, then, of course, you should not connect the bases, at least with your own hands.

If you still want to, then contact a professional, and he will already decide how to do it right. And so, it is still better to use a deformation seam.

Strip foundation

And now, finally, we will take a closer look at how to make the foundation with your own hands. And we will start with the strip foundation.

To do it yourself, you need to perform several actions in a certain sequence.

And we present you with a clear and really correct instruction on how to make a strip foundation for an extension to a house:

The first step is to mark up and trace the place where we are going to build the structure. This should be done with a rope and wooden pegs;
Next, you need to dig a trench along our markup. It is best, before pouring concrete, to fix the reinforcement that would connect the foundations of the main building and the extension. The width of the trench itself should be approximately 150–200 mm greater than the planned extension wall thickness;
Further trench requires careful preparation. It is necessary to fill it with a sand pillow and compact it very carefully. Be careful not to damage the edges of the trench when doing this. It is correct to make a sand cushion with a thickness of 100-120 mm, no more;
The next step will be backfilling and ramming the rubble according to the same principle. We do everything with our own hands, here modern technology is unlikely to help;
Then we lay the waterproofing film in the trench. You will do everything right if you lay it in such a way that its edges come to the surface about 30-40 cm from the edge of the trench;
A special reinforcing structure is installed on top of the waterproofing film, which will ensure stability and integrity of our foundation. This design must completely repeat the size and shape of the foundation, as well as its height;
And finally, we begin to fill the trench with a special mortar, which consists of cement and gravel. We pour the first layer up to 1/3 of the trench, and after it dries - up to 1/2. It is allowed to use foam blocks, but keep in mind that the use of foam blocks is not possible in all cases. Read more about building a foundation from foam blocks under the instructions;
After the cement-gravel layer has completely hardened, we make a wooden formwork with our own hands;
And now, in this wooden formwork, you can completely, to the very brim, pour concrete. After the concrete is completely laid, it is necessary to pierce it in several places so that no air bubbles remain inside. It will be correct from time to time to lightly tap on the concrete so that it is well compacted. Then it will need to be sprinkled with water for several more days;
When it becomes absolutely clear that the concrete is completely frozen, the formwork is removed;
At the very end, before the walls are erected, the almost finished structure must be covered with a waterproofing material. It can be tar, roofing material, bituminous mastic or liquid rubber.

It is worth saying that some people decide to make a strip foundation from foam blocks.

This can be seen rarely and not in all countries, because it is a light and not very dense material that cannot withstand heavy loads.

In our climatic conditions, the concrete foundation does not always support the weight of the structure.

A brick or wooden house on such a foundation of foam blocks definitely cannot stand.

If you make a classic concrete structure and put a house on it from the same foam blocks, you can reduce the load on the base, and therefore extend the life of the foundation. Take note.

And without departing from the problem raised, we note that an extension of foam blocks can even be placed on pile foundations (of course, if it is not very large).

Column Foundation

If you are planning to make a small and not heavy house from boards or some other light material, then you can build an inexpensive columnar foundation.

As a rule, it is made of brick or concrete. For a small extension (for example, 7 × 3), only six support pillars will be enough.

It is also best to make such a foundation strictly according to the instructions, without deviating from a single point.

We dig holes, which in depth will necessarily be below the freezing level of the soil. Consider this factor;
A sand cushion is poured and compacted at the bottom, after which reinforcement made of metal or fiberglass is installed. If you decide to use metal reinforcement, then it will have to be additionally treated with a moisture-proof material. Fiberglass reinforcement does not need this;
We install wooden formwork to the size of the pits;
At the end, the structure is filled with concrete. We are waiting for it to harden, and that's it - now you can build an extension. If necessary, bricks are sometimes placed on top of the concrete to increase the height of the pillars.

Foundation on screw piles

The foundation on piles is the cheapest and easiest type of foundation for construction. As you already understood, it is not able to withstand a lot of weight, so it is not suitable for large and heavy outbuildings.

Most likely, on such a foundation, the maximum that you can build is a wooden veranda.

This type of foundation is characterized by high speed of its creation and ease of installation. Even an inexperienced person can easily screw the piles with their own hands.

Building a foundation is not as difficult a task as it might seem. The most important thing is to have the desire and strictly adhere to the recommendations set out in the instructions, which will tell you how to pour the foundation for the extension.