Expanding living space is an extremely important step that takes place after the construction of a wooden or brick house. But not many people know how to make a foundation for an extension to a house.
There are methods of rigidly connecting foundations or separating foundations and walls with a construction seam. This article will discuss step-by-step instructions on how to properly make a foundation for different types of extensions.
Types of foundation for extensions
Strip foundation - a reliable foundation for an extension There are various designs that differ in construction procedure and strength.
Each has its own parameters and characteristics that affect the complexity of the construction.
The main types are:
- tape;
- columnar;
- pile;
- tiled.
For a strip foundation it is necessary to dig a trench If you plan to build a veranda, a strip foundation would be a good solution. It is a common type and is suitable for both lightweight and massive extensions.
The differences will be in the depth of the foundation and the presence or absence of reinforcement. For such a foundation, a prerequisite is laying it in a trench.
In the following diagram you can see options for placing the main building and an extension based on a strip foundation.
It is recommended to build a columnar base for a small veranda A building on a columnar foundation is erected by placing metal pillars or reinforced concrete into the ground. However, this method is not recommended if you plan to add a massive room.
A columnar foundation is suitable for a small veranda made of wood or plastic. The base structure can be made in the form of separate pillars.
A pile foundation is a structure made up of a large number of piles connected using a cement mixture. This method is suitable for adding heavy structures, such as a basement.
Often the foundation of the attached room is the same as that of the main building.
Attaching a new foundation to an existing one
Reinforcement is used to connect two buildings There are 2 main methods of building a foundation:
The second method is more difficult to implement, but it is more reliable. It will be necessary to correctly calculate the depth of the foundation to prevent possible shrinkage of the building.
It is necessary to use the connection method only if the soil is slightly heaving. In this case, it will be possible to easily predict the shrinkage process of the base.
Filling the base for the extension
Experts recommend constructing an extension structure of the same type as that under the main building.
To get the dimensions of the future foundation, you need to dig up the finished foundation, then calculate its depth and width.
A soil analysis is also carried out in advance, this will help determine its structure and the likelihood of shrinkage.
For work you will need the following tools and materials:
- cement with grade M200 or M300;
- fittings with a diameter of 10 mm;
- river sand;
- gravel;
- wooden boards;
- wire and nails.
Concrete must be poured within one day How to properly pour the foundation for an extension? To do this, you must adhere to the following procedure:
- The area is being marked. To do this, stakes are laid around the perimeter of the extension, and string is stretched between them.
- According to the previously identified dimensions, a trench is dug.
- Drainage is made at the bottom - a cushion of sand and gravel.
- The formwork is installed using boards.
- The fittings are installed and connected to each other with wire.
- The cement mixture is poured. The walls are built only after a few weeks, first the structure is waterproofed. During this time, the cement will have time to dry completely.
Foundation for an extension to a house made of foam blocks
How to make a foundation for an extension to a house from FBS? This design is often erected for an extension to a wooden house.
The material of the blocks is light enough, so there will not be much pressure on the soil.
FBS blocks are also installed in the trench and fastened together with a solution The guide to building a foam block foundation for an extension to a house with your own hands is as follows:
- A trench is dug out.
- A layer of sand and gravel is prepared.
- Waterproofing is being installed. For such a process, you can use roofing material or film.
- The foam blocks are laid on cement mortar.
- It is extremely important to waterproof the top and sides, as well as insulate the base. This is due to the fact that the material is quite hygroscopic and has low resistance to temperature changes.
Extension to a house on screw piles
If the soil on which the construction is planned is weak, and the extension will exert a large load, you will need to use piles. The instructions for this work are quite simple:
- Screw piles are laid in the ground to the required level. They should protrude slightly above the surface, so preliminary calculations will be required.
- Platforms are attached to the top using a threaded connection.
- To increase the reliability of the foundation, you will need to combine the supports. To do this, you can use materials from timber or frame beams.
- An important nuance of such an extension to a wooden or brick house is the need to control the height difference when installing piles. You will also have to take into account the difference in the potential for movement of an object when the soil moves or heaves. For more information on how to make the base of an extension, see this video:
Foundation for an extension on slabs
This method of extension is used if the thickness of the brick house exceeds 40 cm and in slightly heaving soil.
It makes it easy to tie a new foundation to the old one, thanks to the possibility of using reinforcement.
The procedure is as follows:
- The dimensions of the slab are determined.
- A hole is dug out of sand and gravel for the cushion.
- To connect the foundations, you will need to use a rigid fastening method. Holes are made in the old slab, and their diameter should not be larger than the steel rods. The amount of reinforcement is taken based on the type of attached veranda.
- The rods are mounted in the holes made, and they should protrude strongly.
- Formwork made of wooden boards is installed.
- The mixture is poured. For more information on how to quickly make the foundation of an extension, watch this video:
If a floating foundation is planned, it is built separately from the base of the old building.
As can be seen from the article, the extension to the house has a foundation. It can be of different types and constructed from various materials. You can carry out the work associated with it yourself, the main thing is to carefully follow the process technology.
Increasing the usable space in a private property by adding new premises that stand on their own foundation begins with solving the problem of how to connect the foundation to the house so as not to damage both structures. The construction of additional structures usually begins after several seasonal cycles, during which financial resources have been accumulated, a desire has appeared for a new round of site development, and the standing buildings have begun to shrink normally in the ground. Building codes provide the answer to how to connect two foundations to each other, taking into account mutual influence.
Connection requirements
It is necessary to determine how to connect the new foundation of the extension with a residential building at the design stage, taking into account already existing factors. These include the following incoming conditions:
- type and design indicators of the foundation of the existing building;
- characteristics of underlying soils;
- time elapsed since the previous construction (the main shrinkage occurs in 1 - 2 years);
- commensurability of the weight load of 2 structures that need to be combined.
Full requirements for the calculation are contained in the set of rules SP 50-101-2004, which was developed in development of the regulatory rules contained in SNiP 2.02.01-83 *, SNiP 3.02.01-87.
In any case, the help of experienced professionals is not superfluous, since mistakes can be costly later.
The result of linking the base and attached building structures with different values of foundation shrinkage is shown in this video
The construction of a new building begins depending on the season. In the spring, it is not recommended to start laying next to existing foundations, since at this time of year the soils are in the most loose and water-logged state. The settlement value of a new extension on heaving soil may be much greater than the calculated value in the project and may be uneven around the perimeter. At the same time, there is a risk of movement of the undermined old support due to the high groundwater level in combination with possible precipitation (rain or snow).
Before starting work, it is necessary to take into account that any new foundation (MZLF, piles, pillars, slab) will certainly settle, even if it is made identical to the existing support.
Shrinkage
In construction, there are established settlement standards for various structures, the foundations of which are designed and manufactured in accordance with current state standards.
You can find out the standard and make a forecast for the design of your individual home using data from the reference tables:
When comparing the calculated indicators, a new support unit is attached to the foundation of the old building at a given depth, taking into account its own settlement after a certain time.
The upper marks of monolithic strip foundations of combined buildings are made according to calculation, and not according to level, as in this photo.
It is the possibility of displacement relative to each other that determines what kind of connection between two foundations can be made. The following types of connections are used:
- Rigid bond (concrete with reinforcement).
- Separate installation (installation of an expansion joint taking into account the mutual influence of the supports).
The possibility of a rigid connection into a single structure is significantly influenced by the geological factors of the site - in case of mobile or heterogeneous soils, for buildings with a large support area, it is necessary to make intermittent foundations (sometimes with different widths of the tape).
Starting the independent construction of a new extension module to a residential building is permissible if the following requirements are met: issue permits for the installation of a new structure, maintain distances no closer than the minimum permissible to nearby buildings and communications, ensure independent settlement of all structures in relation to each other.
Combining foundations
It is best to attach a new room to the existing foundation of the house using a rigid coupling. In this case (if all conditions are correctly taken into account), it is possible to connect the above-ground surfaces into a single whole without the expectation that gaps and distortions will appear between the elements and the floor level. But such a design solution is limited to sites with non-heaving soils that have high load-bearing characteristics.
In practice, this method is used for low-rise buildings, provided that the extension being built is functionally connected by one roof to the building that is already in use.
Another condition for unification is the same type of foundation. If the strip base of a residential building turns out to be insufficiently wide, then it needs to be strengthened.
Such work includes connecting the reinforcement of an old support with a new frame or laying connecting anchors by drilling, followed by filling the belt with branded concrete. The reinforcement belt prepared for applying the solution is shown in this photo.
The connection of buildings consisting of several floors is carried out according to a more complex scheme, which involves the construction of covering walls with dividing seams on each side, as shown in the drawing.
The rigid type of connection is chosen for cases when the problem of how to connect an old established foundation with a new building is considered, for buried strip foundations. The extension is also designed with a monolithic reinforced concrete structure.
Strip foundations
For a permanent building attached to a house, with a commensurate weight of the building materials used, a stable support of a large area and load-bearing capacity is necessary. This request corresponds in most cases to a strip foundation.
- Expose the entire depth of the existing tape. You need to dig a trench in parts (1.5 m - 2 m), not along the entire length at the same time, since the exposed part loses lateral support, which can lead to its deformation. An old building can be further strengthened with inclined supports.
- Drill holes along the side of the connection corresponding to the size of the reinforcement Ø. In the middle of the tape, holes are drilled in a checkerboard pattern with a depth of about 0.75 of the width of the foundation itself, in the corners - 0.5 m. Reinforcement is driven into the middle holes, in which longitudinal slots are made with an inserted wedging liner for strong fastening in the hole. Reinforcement Ø 14 mm, having a periodic profile, is driven into the corner holes. The output of rods must be at least 0.3 - 0.4 m.
- The frame of the new foundation is knitted and welded to the released reinforcement.
- Fill with concrete mortar.
If there is access to the subfloor for work, the holes for pin-type tension elements can be made through, with the rods secured by flat plates.
Rigid connections of tapes in the form of an open contour (U-shaped) are made in the same way, but the reinforcement is placed in rows with smaller spacing. If the connection side is long in the open strip, you can make several additional support points different from the monolith, as can be seen in the photo.
If there is a need to change the depth of support on the soil of the foundation being added, it is filled with ledges, the height of which varies in steps of no more than 0.5 m. The first ledge is located at a distance of about 1 m from the old foundation. The connection is made with a reinforced concrete strip of the same thickness as the existing foundation of the house.
Each option for rigid connection of foundations has its own characteristics for specific cases, which it is advisable to entrust to professionals to consider and calculate.
Plates
It is possible to ensure the rigidity of the connection between the slab foundations of the house and the extension provided that they are sufficiently thick, about 0.4 m, and also if the old slab protrudes beyond the boundaries of the supporting walls of the building. Such protrusions are usually left during the construction of aerated concrete cottages. The outlet dimensions must be at least 0.3 m. This will make it possible to clean the reinforcing mesh of the slab and make a welded connection to the frame of the new extension.
The connection of monolithic bases is carried out according to the following scheme:
The slab of the old house, which has already settled, in this case not only becomes one with the new fill, but also receives additional reinforcement in the vertical connection of cement mortars due to 0.2 m - 0.3 m of fill underneath it.
Separate supports
If there is a large discrepancy in the weight of the old and new structures, the degree of shrinkage of these structures will differ significantly in magnitude. In such cases, it is not recommended to make a rigid connection for the foundations - it is necessary to choose separate construction of the supporting elements. It is possible to attach other types of foundation to the existing foundation and to do this use the principle of connection through an expansion joint.
The weight of the ceilings and walls of the extension should be distributed over its own support area, without creating tearing forces for the main foundation of the building.
Depending on the operating conditions, the expansion joint can be:
- sedimentary;
- temperature;
- seismic.
The sedimentary option (in the absence of other significant influences) has a width of 1 - 2 cm. According to the conditions of the mutual influence of the supports, attachment to the load-bearing wall of an old house can be carried out with a deformation gap reaching 0.2 - 0.4 m, filled with elastic, moisture-proof material.
Frame wooden extensions are successfully operated on a pile foundation with a metal grillage, as in this photo.
Light verandas or summer kitchens can be built on screw piles, even if there are already several nearby buildings around. This is especially convenient if the site is located on a slope, slope or with uneven occurrence of hard supporting rocks.
At the design stage, the external design of expansion joints that visually separate the facade is envisaged in an open or hidden form, for example, hiding the gap with a subvertical drainpipe. On the façade side, they are usually covered with strips of a special flashing and sealed with low-strength decorative material, which will not prevent the outer walls of buildings from moving relative to each other with possible uneven settlement. Under the roof deck, gaps are bridged using a compensation device.
An extension to a house, installed on separate supports, is a much less labor-intensive process than installing a rigid link, requires significantly less time and financial costs, and can also be done with your own hands without ordering special equipment
A far-sighted solution is to provide for the possibility of an extension at the design stage of the main building of a private house. This will greatly simplify subsequent work and will contain ready-made design solutions, planned uniform settlement over the entire area of the foundation and will ensure the reliability of the foundation.
Owners of private houses often add additional premises to the main building. The need to expand the usable area arises during the operation of the house, the growth of the family, the emergence of financial opportunities and the desire of the owners. Extensions can be used for various purposes; in any case, they must stand on a solid foundation, a foundation. According to building regulations, an extension is considered to be any room located outside the boundaries of the main walls.
Peculiarities
The difficulty when adding additional premises is the presence of a ready-made old building, which has already undergone shrinkage and has certain defects and design features. All these points should be taken into account when designing an extension. It is necessary not only to build a room that is durable and harmoniously suited to the rest of the ensemble, but also not to harm the finished house or contribute to its deformation or destruction. Errors and miscalculations in the design and arrangement of the foundation are unacceptable; they lead to serious consequences and problems for the entire building.
It is very important to make a strong connection between the new and old foundations.
There are two ways to connect bases.
- The expansion joint is simple to make, suitable for all types of foundations, and less expensive. In this case, both foundations are independent of each other under shrinkage or deformation loads. A layer of waterproofing and thermal insulation is laid between the main structure and the attached one, and an expansion joint is formed. The roof of the extension with this method must be separate.
- Rigid reinforcement is more reliable and durable; it is used for old buildings that have completely undergone shrinkage, over 15 years old, in the presence of a high-quality foundation. The connection is made using metal reinforcement. If a new and already finished building is planned to be combined under one common roof, then the connection must be made rigid. The only obstacle to using this method is heaving soils.
Kinds
When building extensions for various purposes, it is worth taking into account the design features, soil properties, and the type of foundation of the old house. Different types of foundations are used, which differ in execution technology and technical characteristics. It is recommended to choose the same type of foundation for a new room as for an already built house. Too different characteristics can lead to different subsidence, deformation and even collapse of the entire building.
The strip foundation will support both a light veranda and a heavy structure. To evenly distribute loads and avoid deformations, the strip base must be a closed loop.
Columnar foundations are used in the construction of lightweight structures, it is affordable and easy to implement. Vertical pillars are located at a distance of 1.5–3 meters from each other. The material used in the pillar method is brick or reinforced concrete. Larch timber is used less often, as it is expensive and rots over time. Despite the grillage, the columnar base is unstable. When constructing a columnar foundation, you cannot dig a basement, which is the only disadvantage of this simple and reliable foundation.
Screw piles, united by reinforcement or an additional tape contour, have a high load-bearing capacity and can withstand heavy capital structures. They are made from reinforced concrete, steel, asbestos or wood. The piles rest on deep load-bearing layers of soil, so they are not subject to displacement or deformation due to heaving. This foundation will not sag.
TISE technology has a number of advantages. It is similar to the construction of a pile foundation due to high reinforced concrete grillages. But there are also disadvantages.
This is a new technology that is still being studied in the long term, but is already quite popular among builders due to its availability and versatility.
The piles are equipped with a special extension at the end, the so-called heel. It prevents the piles from rising during soil heaving and allows construction to be carried out in conditions of permafrost and increased seismic activity.
If the main house stands on a floating slab, then it is necessary to attach a new room on the same independent slab, laying an expansion joint between them.
Rigid connection is possible if the slab thickness is more than 400 mm, or the slab protrudes beyond the base by at least 300 mm, in this case the reinforcement is exposed with partial destruction of the concrete and welded to the reinforcement of the new base. The monolithic slab is durable and will perfectly withstand the heaviest buildings even on difficult soils.
Selection for different buildings
To choose the right type of foundation for an extension, you should first study the condition and dimensions of the foundation of the main building and the type of soil. You can do this yourself. To do this, next to the old house you need to dig a pit with dimensions of 100x150 cm. In a columnar foundation, the depth of the piles and their dimensions are measured, in a strip foundation - the width of the base and height.
If the foundation of the main building is strip, then the adjacent one should be made strip; if it is piled, then the additional one should be the same.
For lightweight frame extensions to a wooden house, a budget option with a columnar base will be sufficient. This base is suitable for all light types of verandas, terraces, porches, dressing rooms and vestibules. The depth of the new and old foundation should be equal. On swampy soils with a high groundwater level, you should choose a pile or columnar foundation.
Brick houses most often have a strip foundation, so it is also recommended to add a strip foundation. Several types of ligaments are made between the bases.
- Rigid connection of bases with a closed loop. For such a bundle, you need to drill holes in the finished tape to a depth equal to 35 diameters of the connecting reinforcement. They are arranged in a checkerboard pattern in two layers, then rods 70-100 cm long are inserted into the holes. You can secure the reinforcement in the old foundation using the wedging method, when notches are made at the end and when driven into concrete, wedging occurs, or you can use a chemical anchor. Then the new reinforcement cage is tied with rods.
- If a new foundation is planned with an open contour, then a rigid connection is made only at the joints with the existing foundation.
- The technological seam with a closed tape contour is made from sheets of polystyrene foam 5 cm thick, which is laid between two bases and at the same time is a vertical element of permanent formwork.
- An open circuit with a technological seam is arranged according to the above scheme, only the insulation is placed at the junction of the circuits.
Premises made of foam blocks can be attached to existing buildings made of any materials.
Foam concrete has low shrinkage rates and is light weight; you can build the walls of an extension from it on your own without the involvement of experienced builders.
If the house has a basement and several floors, the walls of the building are wider than 40 cm, the soil is complex and large loads are planned, the best option would be a slab base in which the loads are distributed over the entire area.
Necessary materials
Before arranging the foundation for an extension, you need to carefully prepare.
Study the initial parameters, create a project, calculate the estimate, prepare the necessary tools and materials:
- cement grade M300;
- sand for drainage;
- reinforcement rod with a diameter of 10 mm;
- boards for formwork;
- nails for fastening;
- gravel to create a pillow;
- rope and pegs for marking;
- wire for strapping.
Self-production
The most common is a strip foundation, which can be used to build a veranda and an extension to an existing house of any design, from a light gazebo to a heavy two-story one. It can be connected to an existing foundation.
To properly fill it with your own hands, you need to study the technology and complete all stages of the work.
- Make markings using stakes and rope, drive pegs around the perimeter of the extension, and pull the string.
- Dismantle the existing blind area, remove the insulation if it was laid.
- Dig a trench according to the rope marks and the intended depth.
- For drainage, you need to make a sand and gravel cushion and compact it thoroughly.
- Assemble the formwork from boards, support it on the outside with special supports, and on the inside with spacers to prevent movement during pouring.
- Install reinforcement in the trench and connect it with wire in the form of a lattice, which should be 20 cm above the ground surface.
- Drill 35 cm long blind holes in the finished foundation of an old house to connect the bases.
- Place reinforcement in the holes, wedge the rods at the ends and tie them to the new frame. Thus, produce a rigid coupling of the foundations.
- If it is decided to make an expansion joint, then wide sheets of heat insulation are laid between the bases.
- Pour the solution, the drying time and strength gain is 3-4 weeks. During this time, it is necessary to moisten the soil next to the formwork, then the concrete will dry evenly, without cracks or deformations.
- After the concrete has dried, a layer of waterproofing is laid, then the walls are erected.
If the soil on the site is weak, and the veranda or gazebo is quite heavy, then it makes sense to make a pile foundation. A massive fireplace built into the wall, a swimming pool, or a two-story building can provide a greater load.
The pile foundation is made as follows:
- screw piles are buried into the soil so that their upper part protrudes above the surface;
- special support platforms are attached on top;
- using a timber or frame beam, they combine all the screw supports into a single structure;
- Careful control of height differences when installing screw piles is very important.
In case of adding a pavilion with a swimming pool, you must:
- mark the dimensions of the veranda and the pool itself;
- dig a pit under the bowl, adding 1 meter to the length and width to provide side cushions and allow passage for builders;
- the walls of the pit are dug with a slight slope for strength;
- a drainage cushion is poured at the bottom, the bowl is waterproofed and thermal insulation is laid;
When completing the construction of a main private house, the question quite often arises: how to make a foundation for an extension to the house and what supporting building structure is best to use for such (relatively light) structures in the form of a terrace or veranda?
It also makes sense to take into account what kind of house the building will be built on: wooden or brick.
If you look closely at houses, cottages and other residential structures that were built a long time ago, you will see that in most cases they have various extensions that are an integral part of such structures. These extensions can remain integral with the overall structure.
In most cases, they were built with their own hands without a foundation, which is why some of these extensions often separate, rise relative to the main structure in winter (due to heaving of the soil), or crack. These occurring defects are due to the fact that during their construction, sufficient attention was not paid to the foundation and technology of their construction.
Let's consider the algorithm for building the correct foundation for an extension with your own hands, if you decide to add an additional room, kitchen, veranda or room to your house.
Preparatory work
Foundation for an extension to a wooden house Before you start making the foundation for an extension to the house with your own hands, it is imperative to carry out preparatory work. They can be divided into the following stages:
The first thing you need to do is decide what kind of extension you will have to build: a room, increasing the space and size of an existing room, a kitchen, a veranda, a terrace or a utility room. Draw a drawing where you indicate the perimeter of the foundation, the thickness of the walls and what kind of ceiling there will be. After this, calculate the estimated load, taking into account the precipitation that will linger on the roof. This is done with the help of reference books.
The next stage is to determine the type of foundation that is located under the frame of the house itself, its thickness and width, as well as its depth. If all this is known, then there is no need to dig a special pit (pit). If there is no such information, then you will need to proceed as follows:
In the first type, the connection of two foundations occurs on the basis of reinforcement as follows. At the base of the house, holes are drilled (in a checkerboard pattern) along the diameter of the reinforcement and to a depth of approximately 35 of its diameters. After that, reinforcement is driven into them, part of which remains outside. Other metal rods (reinforcement) included in the reinforcing stack of the additional base are connected to it (using wire or welding). This compound is ideal for non-heaving soils.
The second type uses the following construction. Between the walls of the foundation of the house and the extension, a distance of 2-5 centimeters is made, into which you can place tow or boards treated with resin or mastic. This type of connection is used on those soils that are heaving.
The last stage is determining the type of foundation that will be used for the extension, and they are as follows:
- tape;
- pile;
- pillar;
- tiled.
In general, strip and columnar bases are most common. When the preparatory work is completed, the material has been purchased, you can begin the construction of the structure itself.
The procedure for constructing the foundation of an extension
In order to make a foundation for an extension with your own hands, it is best to follow the instructions that were developed by specialists; let’s look at it using the example of a strip foundation.
Strip foundation
General recommendations: the base tape must be buried to the same depth as the main house, and there must be an expansion joint between the foundations of the extension and the private house. The width of the strip base can be calculated based on the convenience of the structure, in the case of a light extension. Let's consider the general stages of construction:
Columnar foundation
Let's look at how a columnar foundation is built. To do this, we need to calculate the number of pillars, which depends on the weight of the building. For a small one, you will need about 6-7 pillars (under each corner and in the center), and for a heavier one, from 8 pillars.
The approximate construction stages are as follows.
- the first thing you need to do is dig holes for the pillars, at the bottom of which build a sand and gravel cushion and compact it;
- then a waterproofing layer is applied, reinforcing mesh and formwork are made, and concrete is poured.
The monolithic columnar bases themselves must be made slightly smaller than the required height, so that adjustment can be made using bricks.
If we talk about a pile foundation, it will follow the example of pillars. But for more accurate information, you can seek advice from specialists or reference materials; it all depends on the weight of the attached structure. How to drill piles correctly is described in other articles. Please note that the pile structure is not suitable for heavy extensions.
Conclusion
In order to make a foundation for a house extension with your own hands, you must first determine the weight of the extension and its foundation. First of all, this is preparatory work, as a result of which the developer will decide what exactly he wants to see and what type of foundation he will use.
A few words about how to ensure that both independent foundations (extensions and houses) do not float among themselves. To eliminate seasonal fluctuations and minimize heaving under the foundation of the extension, it is recommended to make and insulate the blind area, the plinth and the base itself. That is, it is necessary to prevent freezing under the sole. To do this, draw a section to scale on the diagram, and calculate the width of the insulation of the foundation blind area so that from its edge to the bottom of the foundation there is a distance no less than the depth of soil freezing. Thus, the deeper the foundation lies, the narrower the required width of the blind area insulation.
