Domestic private construction rarely uses slab foundations. However, all over the world it is used very extensively for the construction of a wide variety of buildings. The properties of such a foundation make it suitable for a wide variety of climatic zones. Of course, in addition to significant advantages, there are also some disadvantages. But more about everything ...
Content:
- Advantages and disadvantages ↓
- Description ↓
- Scope of application ↓
- Laying technology ↓
- Types of foundation slabs ↓
- Composition ↓
- Layer description ↓
- Reviews ↓
The concept of a slab foundation means a slab of reinforced concrete. It is installed under the entire building area. In this case, the slab can be installed both at ground level and buried in the ground. The purpose of the slab foundation is to distribute the load over a larger area, which prevents deformation of the erected objects during ground movements.
The thickness of a reinforced concrete slab for a slab foundation can vary from 20 to 40 cm. Laying the slabs involves preparing the ground and arranging a "cushion" of sand.
Advantages and disadvantages
The most important advantage of a slab foundation is its large support area, which significantly reduces the pressure exerted on the ground. As a result, uneven settlement of the building and deformation of the walls are excluded.
Other advantages include the following:
- ease of installation;
- safety and long-term guarantees of strength;
- opposition to both ground and ground waters;
- preventing soil movement;
- the likelihood of arranging the basement;
- use of the slab as the basis for the floor of the first floor.
A significant disadvantage of the slab foundation is its cost, which is higher in comparison with other options. However, they are justified due to the guaranteed reliability of the slab foundation in front of negative natural conditions.
Description
There are two types of slab foundations: classic and floating:
- Classic type foundation located below the normal level of soil freezing. This allows you to complement the building ground floor or basement.
- Floating type of slab foundation is laid to a depth of 70-90 cm from the surface of the earth, which excludes the possibility of building in depth.
The following types of slab foundation are also distinguished:
- Usual. Its laying is possible by digging an ordinary foundation pit, which is then compacted and leveled. In this case, the minimum thickness of the "pillow" must be at least 15 cm.
- Solid (monolithic), or insulated. Such a foundation is most often used in cold climates.
- Solid slab foundation. It is mainly used for the construction of large objects.
Scope of application
The use of a slab foundation is considered the best option when building houses from a wide variety of materials, both light and heavy. Its device is allowed on any type of soil, from sandy to peaty. The slab perfectly evens out vertical and horizontal ground movements. Such a foundation is not afraid of groundwater, which has a rather large impact on it.
Due to the high costs of concrete and metal, slab foundations are rarely used for the construction of objects with a large building area. They are most often used in the construction of small buildings. It is effective to use slabs as a foundation on soils subject to excessive activity and heaving, as well as in regions with high soil moisture or high groundwater levels.
In private construction, a slab foundation can be combined with buildings made of any materials. It can be frame houses, timber houses or SIP panels, brick or aerated concrete.
Laying technology
At the initial stage of laying the slab foundation, it is necessary to study the soil at the site of the proposed construction of the object. This procedure is necessary to determine the thickness of the "sand cushion". Only then is the final draft drawn up.
Installation of the slab foundation takes place in the following order:
- The upper soil layer is removed, the foundation pit is dug. Its depth should exceed the depth of soil freezing. The bottom of the pit is leveled and rammed.
- A sandy "pillow" is laid, which is also leveled and compacted.
- Waterproofing and drainage system is being installed.
- Around the entire perimeter of the future building the formwork is exposed.
- Further, also along the perimeter, fittings are installed (even fiberglass), reinforcement is made.
- Concrete pouring begins. In this case, the concrete mass is poured in layers, 15 cm each. If ready-made slabs are used as a foundation, then a concrete screed is made on top of them.
- The hardened concrete is vibrated, which provides additional strength.
Types of foundation slabs
The slab foundation also differs in the types of slabs used:
- for small buildings, a monolithic slab is used, characterized by the simplicity of the pouring technology and a shallow depth of laying;
- for industrial and high-rise buildings a foundation slab with stiffeners is used, assembled from separate plates, firmly fastened to each other, or a completely monolithic structure is used;
- for the construction of super-stable structures, especially in areas with increased seismic activity, is used box-shaped structure, assembled from prefabricated or monolithic concrete boxes, rigidly fastened to each other.
The parameters of the slab foundation are selected based on the construction technology. Basically, the thickness of the slab is 30-40 cm. despite the fact that prefabricated slabs are often used, a monolithic slab is considered more reliable, providing greater rigidity and reliability of the finished foundation.
From ready-made slabs for slab foundations, the following types are used:
- Shallow foundation slabs. They are installed over the entire area of the building and distribute the load on the ground most evenly. It is recommended to use such slabs for houses made of logs, beams and various wall blocks.
- The Finnish slab is not very thick, but it is very strong and has excellent thermal properties. It is used most often for frame houses and buildings with underfloor heating.
- Floating ribbed slabs are great for changing ground. They protect the building from subsidence, destruction and cracking. The only drawback of such plates is their higher price.
- Warm stove, in other words, Scandinavian or insulated Swedish stove, can be installed on any soil, since it does not allow the soil to swell, and the heat-insulating layer prevents the soil from freezing. Suitable for use as a ground floor floor and for arranging underfloor heating.
- Floor slabs are quite often used in construction to equip a slab foundation, this makes it possible to increase the reliability of the finished structure.
- Paving slabs can be used as an alternative to concrete pouring. At the same time, time costs are significantly reduced, since it is not required to completely fill the slab, it is enough to perform a concrete screed.
To increase the strength of the building, it is recommended to make the slab foundation slightly wider than the main building. An extra meter or two will not make a significant difference in costs, and reliability will increase many times over.
Composition
The composition of the slab foundation depends entirely on the characteristics of the future building. If there are material selection errors, it will be impossible to correct them after pouring. Concrete grade is selected depending on the purpose of the building and weather conditions:
- for one-story auxiliary buildings (garage, summer house, outbuildings), concrete of the M50 brand can be used, subject to the subsequent installation of a screed made of more durable concrete;
- if in winter the temperature drops to -20 degrees, then it is better to use frost-resistant concrete grade F-75;
- for permanently operated residential buildings, you should choose durable concrete of the M200 brand with increased water resistance (at least 95%).
If the entire volume of concrete cannot be poured in one day, then work can be continued no later than 12 hours later. Otherwise, it is necessary to wait 1-2 weeks until the poured layer has completely dried and only then continue pouring, this will prevent the formation of cracks due to uneven drying of the concrete.
Layer description
If we describe the slab foundation layer by layer, then it looks like this (from bottom to top):
- Priming. Before laying the foundation, a pit of the required depth is dug, and its bottom is carefully leveled and compacted.
- Sandy "pillow". Sand is poured onto the ground. Moreover, every 10 cm it is spilled with water and compacted.
- Geotextile. A drainage pipe is laid on it.
- Crushed stone. It is necessary to prevent soil from clogging the drainage pipe holes.
- Concrete screed. Prevents damage to waterproofing.
- Waterproofing. Its installation is necessary, since concrete perfectly absorbs moisture and cracks can form when it freezes.
- Extruded polystyrene foam, for example Penoplex. Required for additional insulation of the foundationespecially in cold climates.
- Protective layer made of polyethylene film.
- Reinforced concrete slab.
Reviews
“The slab foundation was the solution to my problem. I inherited a small plot of land and wanted to build a summer house there. However, I was stopped by the fact that the groundwater is located a meter underground. But with the use of slabs, it didn't matter. "
Igor Sabelnikov, Voronezh
“As a former builder, I can say that a slab foundation is the best solution. It does not sag, excellent thermal and waterproofing properties. A building with such a foundation will be super stable. "
Vadim Reshetov, Saratov
"Hello. I used the slab foundation when building a house on the advice of Western relatives, although initially I planned to use the usual tape. Taking the advice, I didn’t regret it, I am sure of the strength of the building, and I used the concrete slab as the basement floor ”.
Grigory Maltsev, Tomsk