All about foundations for extensions: how to lay a solid foundation

Various annexes, whether it be verandas, terraces or something more massive and capital, like the main house, are being built on the foundation. And the further state of not only the outbuildings themselves, but also the house, will largely depend on the correctness of its foundation, and mistakes are fraught with negative consequences for both structures. To make the extensions only beneficial, consider the main features of the structure of their foundation.

What is the foundation for an extension?

As in the construction of a house, the choice of the type of base is individual and depends both on the characteristics of the site (type of soil, groundwater level) and on the parameters of the extension itself. The traditional types of foundations include:

Tape - as a rule, we are talking about a shallow tape, if the extension is residential, for year-round use, it is advisable to make the tape and the blind area (if any) insulated. The best option for insulating the tape is considered to be a fixed formwork made of a specific heat insulator (PPS, EPS).

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Slab - not only USHP, but also ordinary slabs are now also poured over a layer of thermal insulation to protect the base from moisture and low temperatures.
Columnar - the most common type of foundation, pillars can be either large-format concrete blocks or concrete poured into sleeves of roofing material or asbestos-cement "shell".
Pile - it is also quite in demand for the construction of verandas and terraces, piles are mainly metal, TISE (concrete piles with expansion) are less common, but if the soils are very heaving, they can become real salvation.

Light extensions to seasonal dachas or cabins, from the category of temporary huts that have passed into the category of guest houses, are being erected on original foundations. Most often, obsolete tires are used, laid pointwise under the load-bearing elements or throughout the entire building spot.

How to choose a foundation for an extension?

The main factor of influence when choosing the type of foundation for an extension is the type of foundation under the house - regardless of how the buildings will be connected and whether they will be connected at all, both foundations must "live on one life. " Yes, the extension is in most cases easier at home and does not require a reinforced base, but a tape must be made to the tape, to the posts, pillars, to the slabs, slabs, to the piles, piles. Even if a veranda on a columnar or pile is attached to the house on a strip foundation, then at least the depth of their occurrence must coincide, with an allowance for the shrinkage of the extension.

How to connect the new foundation with the main one?

During the construction of outbuildings, the most important task is to "do no harm", so that it does not turn out that the extension not only deformed itself, but pulled the house along with it. The bulk of the problems arise from the different weights of the buildings, respectively, and the different shrinkage of their bases. If pillars or piles, in principle, do not create difficulties, since we are not talking about any kind of connection, then with ribbons and slabs, troubles are possible after the very first winter. There are two ways to attach the monolithic foundation of the extension to the foundation of the house.

Through the expansion joint - a universal, most common and "safe" option.
Rigid coupling is considered more reliable, but much more difficult to implement, more time consuming and in case of mistakes, not only the extension, but also the house will suffer.

With the advent of modern building technologies and materials, rigid coupling is used less and less, even when the house and the extension are made of bricks or blocks.

How to make an expansion joint when building an extension foundation?

Joining the new foundation to the old one through the expansion joint does not imply any common connections between the bases, even sliding ones. The slab or tape (observing the depth of occurrence) is poured almost close to the main one, with an indent of 2–5 cm. The easiest way is to immediately lay a sheet of PPS or EPSP into the gap, using it as a permanent formwork when pouring the mortar. The absence of rigid fixation will allow the bases to move relative to each other without deformation during movement. Even on the most non-rocky soils, with the exception of rocky ones, the foundation of the extension will shrink, and the expansion joint will level this shrinkage.

How to firmly connect the foundation of the extension to the foundation of the house?

Attaching the foundation of the extension to the foundation of the house in a rigid way is permissible only on non-porous soils, if the house has completely settled down and shrinkage has stopped. It is advisable for the construction of large, massive extensions from small-format or large-format masonry materials. The main "indication" for a rigid ligament is the uneasy construction of an extension, and a major reconstruction of the house, as a result of which both the house and the annex will be under the same roof. Both tapes and slabs, poured close to each other, must be of the same thickness as the main ones; the bundle is made through reinforcement. For a rigid connection, the slab is poured with a thickness of at least 40 cm when there is a protrusion of the main slab from 30 cm.

Is it possible to insure against deformation with a rigid coupling?

In order to reduce possible negative consequences when connecting the foundations of the house and the extension in a rigid way, a number of measures are performed.

Moisture drainage is organized - the more moisture in the soil, the stronger the swelling, a foundation drainage system is laid to drain water from the soil. To drain precipitation and melt water, storm sewers will be organized based on the drainage system. In no case should the drains from the drainage system be run into the drains, they must be discharged through sealed pipes.
They insulate the foundation and the blind area - the insulation is not able to "warm" the earth, but it contributes to the displacement of the depth of freezing into the preparation layer (sand cushion).

Dry soil and insulated foundations significantly increase the chances of successful operation of a house with an extension without permanent sealing of cracks.

Did you connect the foundation of the house with the foundation of the extension? Write in the comments!

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