Cost to turn crawl space into basement

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• Repair or Clean a Crawl Space
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Basement.

Basement construction

The basement is a type of buried foundation. A basement floor is considered to be a floor in which the floor level of the premises is lower than the level of the planning mark of the ground by more than half of their height. The height of the basement is taken equal to 1.9...2.2 m. This is enough to accommodate storage facilities or to install heat generators. If it is planned to arrange a gym or a games room in the basement, then its height is assigned not less than in the living rooms.

In the basement it is convenient to store products, to make preparations. This is due to the property of the soil to maintain an almost constant temperature. At a depth of 1.5 ... 2 m from the surface of the earth, it keeps at a level of 5 ° C - in winter and 10 ° C - in summer.

The basement (semi-basement) floor is buried in the ground no more than half the height of the floor. Quite often, the basement is arranged during construction on difficult terrain. The height of the basement is equated to the height of the living quarters.

Having a basement is a wish of any builder. This is understandable. Useful areas increase without increasing the dimensions of the house. The cost level of housing, if it is supposed to be sold someday, is also rising.

It should be taken into account that the cost of creating a basement is almost 1.5 - 2 times higher than the above-ground floor, if reliable waterproofing from groundwater is required.

At the same time, when the house is located on dry soils, the presence of a basement or basement floor in it is justified and desirable, since the costs for it are 2-4 times less than those required to create an ordinary floor with the same usable area.

Attention!

If you intend to use imported liquefied gas (propane) instead of mains gas as fuel for cooking or heating, it is better to refuse from the basement or basement. This gas is heavier than air. If accidentally leaked, it can accumulate in the lower unventilated cavities of the house and cause an explosion of (Fig. 1).

1

The design of the basement and the foundation under it is determined by the level of groundwater, the degree of heaving of the soil, the type of ceiling and the basement waterproofing scheme.

From the standpoint of the foundation under the house, the basement is made according to two schemes: supported on a slab (Fig. 2, a) and supported on a tape (Fig. 2, b) . Each of them has its applicability and its cost.

Fig. 2

Building a house with a basement with a high groundwater level should be done on a slab. Reinforcement of the slab and its concreting will require a lot of money, but it is much easier to ensure the tightness of the connection between the slab and the basement walls. The thickness of the slab (15 ... 25 cm) depends on the dimensions of the house and the location of the internal load-bearing walls of the basement. The slab reinforcement is a rigid spatial frame laid over its entire area. Reinforcement diameter - 12... 15 mm.

With a high level of groundwater, for those who want to build a house with a basement, you can use a well-known technique. The depth of the pit under the basement is made small, to the level of groundwater. After the construction of the basement, the excavated soil is poured around the future house, which will be on some elevation. The visual image of the house will be more advantageous, and groundwater will not bother you much.

If the groundwater level is low and the builder does not face the problem of ensuring the tightness of the basement, then the basement walls can be supported on the tape. With this design, the basement floor is not power. It does not connect with the foundation tape and with the walls. Tape thickness - 20 . .. 30 cm, width - more than the wall thickness by 4 ... 5 cm.

As for the thickness of the basement walls, it is determined by the building material itself, the heaving of the soil, the depth of the basement into the ground, the length of the walls and the type of floors (Fig. 3) . If the walls are buried in non-rocky soil by more than 1 m, then their thickness is determined taking into account the lateral pressure of the soil (Table 1).

3

Table 1. Minimum basement wall thickness in non-rocky soils

With such wall thicknesses on non-rocky soils, the basement floors do not have to be concrete.

The main task of the builder, who decided to build a basement, is to exclude its moisture from groundwater or flood waters. Capillary moisture should not cause an increase in humidity in the room or dampening the structure of the house itself.

For basement sealing, three layouts of the sealing layer are used:

• external anti-pressure;
• internal anti-pressure;
• waterproofing to protect against capillary moisture.

When performing external anti-pressure waterproofing , it should be taken into account that its upper edge must be at least 0.5 m above the expected groundwater level (Fig. 4, a) . The pressure from the waterproofing layer is transferred to the load-bearing enclosing elements of the floor and walls, which makes it more preferable.

4

A horizontal section of waterproofing is applied over leveled and smooth concrete preparation up to the basement floor. Such a screed with a thickness of 4 ... 5 cm is made from a mixture of sand and cement 6: 1, which is desirable to be reinforced with a mesh. A layer of primer is applied to the prepared surface of the slab, and bituminous mastic is applied to it. After that, sheets of roofing material are laid with an overlap of at least 10 cm. The roofing material should protrude 15 cm beyond the basement walls. In wet soils, insulation is made of two layers of roofing felt or roofing material is used. To protect the insulation from damage, it is covered from the outside with a layer of cement mortar. If roofing is used as a roll material, then tar impregnation is applied to the concrete.

Vertical sections of rolled waterproofing are applied to the walls and protected from the outside with half-brick masonry, concrete slabs or a layer of sprayed concrete. The overlap of the horizontal and vertical sections of the waterproofing is carried out by bending the horizontal waterproofing by at least 15 cm. The vertical waterproofing is removed at least 15 cm above the ground surface.

If the ground waters lie below the basement floor and the soils there are low-moisture, then it is enough to confine oneself to coating waterproofing with the application of hot bituminous mastic in two layers up to 2 mm thick. Before applying the mastic, the walls should be coated with a primer.

The space between the basement walls and the ground is filled with greasy clay, making a clay castle.

Internal anti-pressure waterproofing is arranged, as a rule, in already existing buildings or during repair work related to the elimination of leakage of basement enclosing structures (Fig. 4, b). Since the pressure on individual sections of the walls of the inner caisson can be significant, structural reinforcements are required to perceive it.

Basement waterproofing against capillary moisture does not require high quality work, as was required when creating anti-pressure waterproofing. Of course, this waterproofing scheme is not suitable for protection against pressure water (Fig. 4, c).

Internal anti-pressure waterproofing on plaster mortar has been used relatively recently, with the advent of plaster mortars with a high degree of adhesion and fast setting. With heads up to 2 - 3 meters, which is typical for the basements of residential buildings, the use of such waterproofing plaster compositions and mastics allows you to perform internal waterproofing without creating a caisson, with the transfer of water load to the plaster mortar (Fig. 4, d). As a rule, such a waterproofing option is used during repair and restoration work as an addition to the existing option.

If the sealing layer did not withstand and a leak occurred, then eliminating this shortcoming, even by filling the basement with soil, will not lead to anything good, because it is very difficult for moisture to leave the sealed basement. Therefore, constant dampness in the underground is inevitable, even when the groundwater goes far down. True, one can hope for modern waterproofing coatings, putties. But if floors have already been laid in the basement, finishing work has been completed, then it will not be easy to eliminate such leaks.

Many developers who are just starting their construction path do not take into account the hydrostatic pressure of groundwater. This can lead to the emergence of basements and cellars, inspection pits of garages and sewer cesspools, unfilled pools. All of the above are quite frequent phenomena if the level of groundwater or flood waters is high, and the weight of the structure is small.

From the practice of the river fleet

For a long time, floating landing stages have been used as piers on rivers and lakes - piers, the lower, which is the main part of which is a sealed reinforced concrete hull. On top of it, a light two-story wooden structure of the pier itself is being built .

This is how a house with a basement or cellar should be presented to those who may have ground or flood water levels rising above their floor level.

The tightness of the basement is ensured by the watertightness of the walls and the slab of the house on which it is built.

Fig. 5

From the practice of an individual developer

With a sufficiently high level of flood waters, the developer nevertheless decided to build a basement. The house is small, 6x8 m, you can try. Everything was done almost according to science.

They dug a pit 1.8 m deep, made a backfill of coarse-grained sand, laid waterproofing, and cast a 10 cm thick concrete base on it with reinforcement with mesh (you can’t call such a thin reinforced concrete creation a slab). After that, exactly along the perimeter, the developer laid three rows of FBS foundation blocks and blocked the basement with slabs.

Spring has come. Guard!!! The floor of the basement was strongly raised, water went through the cracks formed (Fig. 5).

What happened?

The hydrostatic pressure acting on the floor from below turned out to be supercritical. When the water level in the soil is 1 m above the basement floor, a pressure of 1 ton acts per unit area of ​​the floor. That is, a force of 48 tons acts from below on the entire area of ​​\u200b\u200bthis basement of 48 m ² . This is the weight of a very heavy tank or a whole wagon. The thin floor couldn't handle it.

How it should have been done. The floor slab must be at least 20 cm thick, and its reinforcement must be correctly performed. Significant strengthening of the basement floor could be provided by the construction of one transverse wall.

If you take a closer look at such a foundation, you will notice that the wall is too close to the edge of the slab on which it rests. Our builder laid the foundation blocks close to the perimeter of the concrete floor. Apparently, he decided to save on the volume of earthworks and concreting. With this design of this unit, the basement floor from the pressure of the soil immediately from the edge begins to be intensively loaded with a bending moment (Fig. 6, a) .

Large bending loads are both significant deformations and breaking stresses in the basement slab. With weak soil compaction under the slab, this manifests itself to a greater extent.

In the variant when the floor slab extends beyond the wall contour by 30 - 40 cm (Fig. 6, b) , the maximum value of the bending moment becomes much lower. The plate could be made thinner without fear of deformation and destruction.

Fig. 6

A similar failure of the floor slab can occur with an unburied slab. A heavy garage can severely deform the slab, especially if its integrity is compromised by an elongated opening for a viewing hole (Fig. 7).

7

When constructing a basement, concrete floors are laid on its walls. This is due to the fact that the lateral pressure of the soil on the walls must be transferred to something. Especially large lateral loading of the walls arises from heaving of the soil, since it tends to expand when it freezes in all directions. Rigid ceilings allow you to close on yourself the loads that fall on the walls of the basement from all sides. This calculation model considers the basement wall as a set of vertically located beams that transfer the load from the soil to the concrete floor and to the concrete floor (Fig. 8).

8

That is why basement walls during construction are loaded with concrete slabs in the same season, without waiting for the heaving soil to tilt the walls inside the basement with its expansion.

This scheme was adopted during the construction of the basement using the TISE technology. Such vertical beams are created in every fourth vertical channel of the wall after they are filled with reinforcement and concrete. This scheme works well regardless of the dimensions of the basement and the breakdown of its internal walls.

This is interesting

With a power scheme representing a wall as a set of vertical beams, the basement walls can be made thinner, the heavier the house is from above (from the conditions of the stress state of the wall, loaded with weight and lateral pressure). Under these conditions, there are no tensile stresses in the concrete mass, from which it could collapse.

When constructing basement walls from ready-made concrete blocks, horizontal reinforcement is performed. In this case, the wall works according to a different design scheme, in which it is considered as a set of horizontal beams that transfer the lateral load from the soil to the external and internal walls of the basement. Due to the large span of such a horizontal beam, the basement wall must have a large thickness or effective horizontal reinforcement (Fig. 9).

9

In reality, the basement wall should be considered as a set of simultaneously working vertical and horizontal beams. Moreover, the heavier the house itself, the more weight the basement walls are loaded with, the closer the design scheme is to the wall with vertically arranged beams.

From construction practice

Basement walls are often erected using large-sized ready-made foundation blocks FBS (Fig. 10). As a rule, when performing corner bonding with these blocks, the overlap of the blocks along the entire length of the wall is the most minimal.

With weak horizontal reinforcement, the narrow area of ​​the vertical joints of the FBS turns into a hinged joint. In the absence of a basement floor and a sufficiently large soil pressure subject to heaving phenomena, part of the wall may go inward.

10

Correcting the situation and stopping the process of destruction of the basement walls is possible only with the erection of reinforcing walls in the basement. This is quite an expensive pleasure, and the basement will lose all its attractiveness.

The basement wall can collapse from the pressure of the soil even without heaving phenomena, during the installation of floor slabs. The truck crane supports, installed in close proximity to the basement walls, create a sufficiently high level of stress in the soil. The load on the retractable support and the lateral soil pressure on the basement walls are especially high when the installation of distant slabs, the furthest from the truck crane, is in progress (Fig. 11).

11

To prevent such destruction, the distance from the wall to the edge of the truck crane support platform must be at least 0. 8 m.

Construction of a basement begins with digging a foundation pit. When planning this stage of work, the developer should not forget that in winter the freezing boundary in the pit area will drop. A soil with a dense structure, when saturated with water and freezing, can reduce its density and rise by 10 ... 15 cm (Fig. 12, a). If the developer managed to build a basement, but did not provide for its insulation, then heaving phenomena can raise the basement by 10 ... 15 cm, causing destruction or unacceptable displacements. To prevent this from happening, the basement should be insulated according to one of two schemes that provide for insulation along the floor or along the basement floor (Fig. 12, b, c). The last option is more successful, since in the absence of overlapping, the walls of the basement can lean inward from the pressure of heaving soil. Snow cover here can be considered basement insulation.

12

When planning the insulation and waterproofing of basement walls from the outside, we pay attention to the quality of their installation.

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