Choosing a foundation for a country house
This question has to be solved by everyone who decided to build their own country house or cottage. From all sides, you are immediately surrounded by "experts" and are loaded with a huge amount of unnecessary and useless information. They especially stress on such a characteristic as frost penetration depth, while none of the advisers can clearly and clearly explain why it is necessary to do so and not otherwise, using only the stories of friends and acquaintances as an argument. Although in reality everything turns out to be much simpler - just look at the construction from the point of view of physical and chemical processes and everything instantly falls into place.
I passed this stage 3 years ago when I took up the construction of a country house with my own hands. Fortunately, then I managed to figure out the whole stream of useless information about how to build and I chose an almost perfect solution for building a country house. Now I want to share my own experience and talk about what could have been done even better.
Let's figure it out!
So.Low-rise individual construction. The first thing you need to decide - the mass of the house. Houses are heavy and light. For heavy homes are all houses with walls of "stone" materials, where cement is used as a binder. Heavy houses firstly have a high specific pressure on the ground, and secondly they do not allow serious deformations of the supporting structures (concrete does not know how to stretch). With light houses, for the construction of which materials from wood are used, everything is much simpler. They have a low specific pressure on the ground and they calmly tolerate the deformations and movements of the supporting structures (not forgetting such a thing as the natural shrinkage of a wooden house when the wood dries out).
This is the first characteristic that determines how much ground pressure your house will exert. If the bearing capacity of the foundation is insufficient, the foundation together with the house will shrink.The larger the bearing area, the lower the specific pressure that the structure will exert on the base.
Thus, the pile foundation will exert the greatest pressure on the foundation, and the monolithic foundation slab will provide the least pressure.Therefore, the pile foundation can be used exclusively for light houses (or for heavy ones if construction is carried out in the permafrost zone - but about this separately).
With the mass of the house decided.The next characteristic is the depth of freezing.What is it and what is it for? Everything is as simple as two and two. As we know from the course of high school physics, when freezing water expands and increases in volume. The soil is soaked with water in the autumn when freezing will expand and push your foundation along with the house up. Even if it is a heavy stone house. Then in the spring the soil will thaw and this part of the foundation will hang in the air. Our ancestors invented a simple way to combat this phenomenon - by deepening the foundation base to the depth of frost penetration (for a specific region of construction). This technique is not effective and leads to a huge waste of resources and building materials.
In order to eliminate frost heaving of the soil, it is necessary either to remove moisture from the soil under the foundation, or to insulate the soil, in order to rule out its freezing.So our task is simplified. Instead of digging into the ground, we need to warm the ground and prevent it from freezing, because even schoolchildren know that cold beats the ground from above, and from below it is heated by the core of the earth.
The reverse approach is required for construction in the permafrost zone, which is a frozen swamp in the tundra. If you allow the thawing of the soil in the summer, then its carrying capacity will decrease and the house built will simply sink. That is why during construction in the permafrost zone, pile foundations are used. The carrying capacity of frozen soil is comparable to rock, but it is necessary to raise the house above the ground in order to prevent the soil from thawing with heat from the house itself.
For light frame structures, you can use a simple pile foundation, because the mass of the building is insignificant, and its design allows for deformation.
If you are building a heavy house, then immediately forget about the strip foundations. This is a useless waste of materials and labor. The only argument in favor of the strip foundation can be a device of a full basement floor or basement over the entire area of the foundation. In all other cases, in low-rise construction it is necessary to use a slab foundation.
As for the foundation under the foundation.Once and for all, forget about such building material as crushed stone.This is a relic of the past, which was previously used as a separating layer to eliminate the capillary suction of moisture (on the basis that there is no moisture - there is no freezing). One of the most serious mistakes is the creation of a rubble cushion under the foundation.
Do a simple experiment. Put a few small stones on the ground or sand and step on them with your foot. What will happen? That's right, the stones are pressed into the ground. The greater the specific pressure, the stronger the stones will go into the ground. This is exactly what will happen whether you have a natural soil at the base or a sand cushion.
To level the base and raise the ground level use only sand. This building material is very easily compacted, and also has excellent drainage capacity. And do not forget that drainage is being laid along the perimeter of the foundation. This prevents the presence of moisture in the soil near and under the foundation. And as you know, there is no water => no freezing => no frost heaving.
The second protection against frost heaving is a device of a heated blind area.After all, slab foundation itself closes the ground from the cold, but its perimeter remains vulnerable.That is why it is imperative to install a warmed blind area, the width of which should be comparable to the depth of freezing in the construction region.
The slab foundation is of two kinds. The first is a classic base plate. Formwork is created, fittings are laid, concrete is poured. After that, the foundation must be warmed around the perimeter and on top. Since the bottom of the stove is not insulated and if you use it as a base of the floor, then in fact you will heat the soil under your house.
The most high-tech type of foundation - insulated Swedish stove (abbreviated USP). It became possible due to the appearance of such an insulating material such as extruded polystyrene foam. Its distinguishing feature is the ability to withstand heavy loads and the inability to absorb moisture. The foundation of UWB is arranged on the contrary - a heater is laid on the base (sand pad), and concrete is poured in from above, in which liquid heating pipes are immediately laid. The advantage is obvious. The foundation is thermally insulated from the ground, which means you don’t heat the ground under the house, you also save concrete and reinforcement, becausethey need 2-2.5 times less than the classic base plate. And immediately get a rough floor in the house, plus a finished heating system.
Here, take a look at this incredible video showing the whole process of building a warmed Swedish plate in Germany:
This is the most correct type of foundation for any heavy houses.Forget all other types of foundations.The same foundation can be made for a light frame house, if you want a solid and reliable base with underfloor heating. The slab foundation can be erected on any basis, without conducting geological surveys, since The average specific pressure on the base of a huge stone house will be lower than the pressure from a single adult.
But do not forget that we are in Russia. And such a wide range of components that are shown in the video, in our country simply can not be found. In addition, construction companies break up space prices for building a foundation using UWB technology. Therefore, the only way out is to do it yourself. Moreover, there is nothing complicated about it.
For those who want more information with links to regulatory documents,I recommend reading: Design and construction of shallow-buried slab foundations of the type “Insulated Swedish stove” (PDF)
In the next part we will consider the choice of wall building materials. To be continued.
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