Modern materials and design solutions for external walls. Structures of external walls of civil and industrial buildings. Brief classification of external walls
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4.1.
Otweet: Yes(file address Block 3) Your answer is correct, because. walls are load-bearing only when they accept load both from their own weight and from others structural elements building. Go to question 4.2
4
4.1.
Otweet: NO(file address Block 3) Your answer is INCORRECT because... YOU did not take into account that walls that do not accept the load from others building elements, belong to the categories of either self-supporting or non-supporting. Go back to reading the text
Structural wall solutions
The thickness of the external walls is selected according to the largest of the values obtained as a result of static and thermal calculations, and is assigned in accordance with the design and thermal characteristics of the enclosing structure.
In fully prefabricated concrete housing construction, the design thickness outer wall linked to the nearest larger value from the unified series of external wall thicknesses adopted in the centralized production of molding equipment: 250, 300, 350, 400 mm for panel buildings and 300, 400, 500 mm for large-block buildings.
The calculated thickness of stone walls is coordinated with the dimensions of the brick or stone and is taken equal to the nearest greater structural thickness obtained during masonry. With brick sizes of 250×120×65 or 250×120×88 mm (modular brick), the thickness of the solid masonry walls is 1; 1.5; 2; 2.5 and 3 bricks (including 10 mm vertical joints between individual stones) are 250, 380, 510, 640, and 770 mm.
The structural thickness of a wall made of sawn stone or light concrete small blocks, the standardized dimensions of which are 390 × 190 × 188 mm, when laid in one stone is 390 and 1.5 - 490 mm.
The design of walls is based on the comprehensive use of the properties of the materials used and solves the problem of creating the required level of strength, stability, durability, insulation and architectural and decorative qualities.
In accordance with modern requirements for economical use of materials, when designing low-rise residential buildings with stone walls, they try to use the maximum number of local building materials. For example, in areas remote from transport routes, small locally produced stones or monolithic concrete are used to build walls in combination with local insulation and local aggregates, which require only imported cement. In villages located near industrial centers, houses are designed with walls made of large blocks or panels manufactured at enterprises in this region. Currently, stone materials are increasingly used in the construction of houses on garden plots.
When designing low-rise buildings, two structural solutions for external walls are usually used - solid walls made of homogeneous material and lightweight multilayer walls made of materials of different densities. For construction interior walls Only solid masonry is used. When designing external walls using a solid masonry scheme, preference is given to less dense materials. This technique allows you to achieve a minimum wall thickness in terms of thermal conductivity and more fully use the load-bearing capacity of the material. It is advantageous to use high-density building materials in combination with low-density materials (lightweight walls). The principle of constructing lightweight walls is based on the fact that the load-bearing functions are performed by a layer (layers) of high-density materials (γ > 1600 kg/m3), and the heat insulator is a low-density material. For example, instead of a solid outer wall made of clay brick 64 cm thick, you can use a lightweight wall structure made from a layer of the same brick 24 cm thick, with fiberboard insulation 10 cm thick. Such a replacement leads to a reduction in the weight of the wall by 2.3 times.
Artificial and natural small stones are used to make walls of low-rise buildings. Currently, artificial firing stones (solid clay bricks, hollow bricks, porous bricks and ceramic blocks) are used in construction; unfired stones (sand-lime brick, hollow blocks of heavy concrete and solid blocks of light concrete); natural small stones - torn rubble, sawn stones (tuff, pumice, limestone, sandstone, shell rock, etc.).
The size and weight of the stones are designed in accordance with hand-laying technology and taking into account maximum mechanization of work. The walls are laid out from stones with the gap between them filled with mortar. Cement-sand mortars are most often used. For laying internal walls, ordinary sand is used, and for external walls, low-density sand (perlite, etc.). Wall laying is carried out with mandatory compliance suture dressings(4.6) in rows.
As already noted, the width of the wall masonry is always a multiple of the number of brick halves. The rows facing the façade surface of the masonry are called front mile, and those facing the inside – inner mile. The rows of masonry between the inner and front versts are called forgettable. Bricks laid with the long side along the wall form spoon row, and the walls laid across - splice row. Masonry system(4.7) is formed by a certain arrangement of stones in the wall.
The row of masonry is determined by the number of spoon and butt rows. With uniform alternation of spoon and butt rows, a two-row (chain) masonry system is obtained (Fig. 4.5b). A less labor-intensive multi-row masonry system, in which one interlocking row of bricks binds five rows of spoons (Fig. 4.5a). In walls made of small blocks, erected using a multi-row system, one tying row ties two trussed rows of masonry (Fig. 4.5c).
Fig.4.5. Types of hand-made walls: a) – multi-row brickwork; b) – chain brickwork; c) – multi-row masonry; d) – chain masonry
Solid masonry of high-density stones is used only for the construction of internal walls and pillars and external walls of unheated rooms (Fig. 4.6a-g). In some cases, this masonry is used for the construction of external walls using a multi-row system (Fig. 4.6a-c, e). The double-row stone laying system is used only in necessary cases. For example, in ceramic stones, void slots are recommended to be located across the heat flow in order to reduce the thermal conductivity of the wall. This is achieved using a chain laying system.
Lightweight external walls are designed in two types - with insulation between two solid masonry walls or with an air gap (Fig. 4.6i-m) and with insulation lining the solid masonry wall (Fig. 4.6n, o). In the first case, there are three main structural options for walls - walls with horizontal releases anchor stones, walls with vertical diaphragms made of stones (well masonry) and walls with horizontal diaphragms. The first option is used only in cases where lightweight concrete is used as insulation, which embeds anchor stones. The second option is acceptable for insulation in the form of pouring lightweight concrete and laying thermal liners (Fig. 4.6k). The third option is used for insulation made from bulk materials (Fig. 4.6l) or from lightweight concrete stones. Solid masonry walls with an air gap (Fig. 4.6m) also belong to the category of lightweight walls, since they are closed air gap performs the functions of a layer of insulation. It is advisable to take the thickness of the layers equal to 2 cm. Increasing the layer practically does not increase its thermal resistance, and reducing it sharply reduces the effectiveness of such thermal insulation. More often, an air gap is used in combination with insulation boards (Fig. 4.6k, o).
Fig. 4.6, Options for manual masonry of walls of low-rise residential buildings: a), b) - solid external walls made of brick; c) – solid internal brick wall; e), g) – solid external walls made of stones; d), f) – solid internal walls made of stones; i)-m) – lightweight walls with internal insulation; n), o) – lightweight walls with external insulation; 1 – brick; 2 – plaster or sheet cladding; 3 – artificial stone; 4 – slab insulation; 5 – air gap; 6 – vapor barrier; 7 – wooden antiseptic strip; 8 – backfill; 9 – solution diaphragm; 10 – lightweight concrete; 11 – natural frost-resistant stone
To insulate stone walls on the street side, use hard slab insulation from lightweight concrete, foam glass, fiberboard in combination with weather-resistant and durable cladding (asbestos cement sheets, boards, etc.). The option of insulating walls from the outside is effective only if there is no access of cold air to the contact area of the load-bearing layer with the insulation layer. To insulate the external walls on the room side, semi-rigid slab insulation (reed, straw, mineral wool, etc.) is used, located close to the surface of the first or with the formation of an air gap, 16 - 25 mm thick - “at the distance”. The slabs are attached to the wall with metal zigzag brackets or nailed to antiseptic wooden slats. The open surface of the insulation layer is covered with sheets of dry plaster. Between them and the insulation layer, a layer of vapor barrier made of glassine, polyethylene film, metal foil, etc. must be placed.
Study and analyze the above material and answer the proposed question.
Dedyukhova Ekaterina
The resolutions adopted in last years. Resolution N 18-81 dated 08/11/95 of the Ministry of Construction of the Russian Federation introduced changes to SNiP II-3-79 “Building Heat Engineering”, which significantly increased the required heat transfer resistance of building envelopes. Considering the complexity of the task in economic and technically, a two-stage introduction of increased heat transfer requirements during the design and construction of facilities was planned. Decree of the State Construction Committee of the Russian Federation N 18-11 dated 02.02.98 “On the thermal protection of buildings and structures under construction” establishes specific deadlines for the implementation of decisions on energy saving issues. Almost all objects that have begun construction will use measures to increase thermal protection. From January 1, 2000, the construction of facilities must be carried out in full compliance with the requirements for heat transfer resistance of enclosing structures; when designing from the beginning of 1998, change indicators No. 3 and No. 4 to SNiP II-3-79, corresponding to the second stage, should be applied.
The first experience of implementing solutions for thermal protection of buildings raised a number of questions for designers, manufacturers and suppliers of building materials and products. Currently, there are no established, time-tested structural solutions for wall insulation. It is clear that solving thermal protection problems by simply increasing the thickness of the walls is not advisable either from an economic or an aesthetic point of view. Thus, the thickness of a brick wall, if all requirements are met, can reach 180 cm.
Therefore, a solution should be sought in the use of composite wall structures using effective thermal insulation materials. For buildings under construction and being reconstructed, in structural terms, the solution can fundamentally be presented in two versions - the insulation is placed with outside load-bearing wall or from the inside. When the insulation is located indoors, the volume of the room is reduced, and the vapor barrier of the insulation, especially when used modern designs windows with low air permeability leads to an increase in humidity inside the room, cold bridges appear at the junction of internal and external walls.
In practice, signs of thoughtlessness in resolving these issues are foggy windows, damp walls with the frequent appearance of mold, and high humidity in the premises. The room turns into a kind of thermos. There is a need for a device forced ventilation. Thus, monitoring of a residential building at 54 Pushkin Avenue in Minsk after its thermal sanitation allowed us to establish that relative humidity in residential premises increased to 80% or more, that is, 1.5-1.7 times higher than sanitary standards. For this reason, residents are forced to open windows and ventilate living rooms. Thus, the installation of sealed windows in the presence of a supply and exhaust ventilation system significantly worsened the quality of the indoor air environment. In addition, many problems already arise when operating such tasks.
If, with external thermal insulation, heat loss through heat-conducting inclusions decreases with thickening of the insulation layer and in some cases they can be neglected, then with internal thermal insulation, the negative impact of these inclusions increases with increasing thickness of the insulation layer. According to the French research center CSTB, in the case of external thermal insulation, the thickness of the insulation layer can be 25-30% less than in the case of internal thermal insulation. External location insulation is more preferable today, but so far there are no materials and design solutions that would fully provide fire safety
building.
To do warm house from traditional materials- brick, concrete or wood - the thickness of the walls must be more than doubled. This will make the structure not only expensive, but also very heavy. The real solution is the use of effective thermal insulation materials.
As the main way to increase the thermal efficiency of building envelopes for brick walls Today, insulation is offered in the form of external thermal insulation that does not reduce the area interior spaces. In some aspects, it is more effective than the internal one due to the significant excess of the total length of heat-conducting inclusions at the junctions of internal partitions and ceilings with the external walls along the facade of the building over the length of heat-conducting inclusions in its corners. The disadvantage of the external method of thermal insulation is that the technology is labor-intensive and expensive, and the need to install scaffolding outside the building. Subsequent subsidence of the insulation cannot be ruled out.
Internal thermal insulation is more beneficial when it is necessary to reduce heat loss in the corners of a building, but it requires a lot of additional expensive work, for example, installing a special vapor barrier on window slopes
The heat storage capacity of the massive part of the wall with external thermal insulation increases over time. According to the company " Karl Epple GmbH» with external thermal insulation, brick walls cool down when the heat source is turned off 6 times slower than walls with internal thermal insulation with the same insulation thickness. This feature of external thermal insulation can be used to save energy in systems with controlled heat supply, including through its periodic shutdown. especially if it is carried out without eviction of residents, the most acceptable option would be additional external thermal insulation building, whose functions include:
protection of enclosing structures from atmospheric influences;
equalization of temperature fluctuations of the main mass of the wall, i.e. from uneven temperature deformations;
creation of a favorable mode of operation of the wall according to the conditions of its vapor permeability;
formation of more favorable microclimate premises;
architectural design of the facades of reconstructed buildings.
Upon exception negative influence atmospheric influences and condensed moisture on the fencing structure increases the overall durability load-bearing part of the outer wall.
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Before installing external insulation of buildings, it is first necessary to carry out examination the condition of facade surfaces with an assessment of their strength, the presence of cracks, etc., since the order and volume of preparatory work depends on this, the determination of design parameters, for example, the depth of embedding dowels in the thickness of the wall.
Thermal rehabilitation of the facade involves insulating the walls effective insulation materials with a thermal conductivity coefficient equal to 0.04; 0.05; 0.08 W/m´°
C. At the same time facade finishing performed in several options:
— brickwork made of facing bricks;
- plaster on mesh;
- a screen made of thin panels installed with a gap in relation to the insulation (ventilated facade system)
The costs of wall insulation are affected by the design of the wall, the thickness and cost of the insulation. The most economical solution is with mesh plaster. Compared to brick cladding, the cost of 1 m 2 of such a wall is 30-35% lower. The significant increase in cost of the option with facing bricks is due to both the higher cost of exterior finishing and the need to install expensive metal supports and fastenings (15-20 kg of steel per 1 m2 of wall).
The structures with a ventilated facade have the highest cost. The increase in price compared to the brick cladding option is about 60%. This is mainly due to the high cost façade structures, with the help of which the screen is installed, the cost of the screen itself and mounting accessories. Reducing the cost of such structures is possible by improving the system and using cheaper domestic materials.
However, insulation made by URSA boards in outer wall cavities. In this case, the enclosing structure consists of two brick walls and URSA thermal insulation boards reinforced between them. URSA slabs are fixed using anchors embedded in the joints of the brickwork. A vapor barrier is installed between the insulating boards and the wall to prevent condensation of water vapor.
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Insulation of enclosing structures outside during reconstruction can be done using a heat-insulating binder system "Fasolit-T" consisting of URSA boards, glass mesh, construction adhesive and facade plaster. At the same time, URSA slabs are both thermal insulating and bearing element. Using construction adhesive, the slabs are glued to the outer surface of the wall and secured to it mechanical locks. Then a reinforcing layer of construction adhesive is applied to the slabs, over which the glass mesh is laid. A layer of construction adhesive is again applied to it, over which the final layer of facade plaster will go.
Thermal insulation walls outside can be produced using particularly rigid URSA boards fixed to wood or metal frame external wall with mechanical fasteners. Then, with a certain calculation gap, cladding is performed, for example, a brick wall. This design allows you to create ventilated space between the cladding and thermal insulation boards.
Thermal insulation interior walls in the cavity with air gap can be produced by device "three-layer wall" In this case, a wall is first built from ordinary red brick. URSA thermal insulation boards with water-repellent treatment are placed on wire anchors, previously laid in the masonry of the load-bearing wall, and pressed with washers.
With a certain thermotechnical calculation with a gap, a wall is then built, opening, for example, into an entrance, loggia or terrace. It is recommended to make it from facing bricks with jointing, so as not to waste additional funds and efforts to treat external surfaces. When processing, it is advisable to pay attention to good joining of the plates, then cold bridges can be avoided.
With insulation thickness URSA 80 mm It is recommended to apply a two-layer dressing with an offset. Insulation boards must be forced without damage through wire anchors protruding horizontally from the load-bearing upper wall.
Fastenings to URSA mineral wool insulation German concern "PFLEIDERER"
As an example, let’s consider the most affordable option with plastering the façade insulation layer. This method has been fully certified in the Russian Federation , in particular, the Isotech system TU 5762-001-36736917-98. This is a system with flexible fasteners and mineral wool slabs of the Rockwooll type, produced in Nizhny Novgorod.
It should be noted that Rockwool mineral wool, being a fibrous material, can reduce the impact of one of the most irritating factors in our daily environment - noise. As is known, wet insulating material significantly loses its heat and sound insulating properties.
Impregnated Rockwool mineral wool is a water-repellent material, although it has porous structure. Only in heavy rain can a few millimeters of the top layer of material become wet; moisture from the air practically does not penetrate inside.
Unlike isolation rockwool, slabs URSA PL, PS, PT (according to advertising brochures, they also have effective water-repellent properties) are not recommended to be left unprotected during long breaks in work; unfinished brickwork should be covered from rain, since moisture that gets between the front and back shells of the masonry dries very slowly and causes irreparable damage to the structure of the slabs.
Structural diagram of the ISOTECH system:
1. Primer emulsion ISOTECH GE.
2 Glue solution ISOTECH KR.
3. Polymer dowel.
4 Thermal insulation panels.
5 Reinforcing mesh made of glass fiber.
6. Primer layer for plaster ISOTECH GR.
7. Decorative plaster layer ISOTECH DS
.
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Thermal engineering calculation of enclosing structures
Initial data for thermotechnical calculation We will accept according to Appendix 1 of SNiP 2.01.01-82 “Schematic map of climatic zoning of the territory of the USSR for construction.” The construction and climatic zone of Izhevsk is Ib, humidity zone is 3 (dry). Taking into account the humidity regime of the premises and the humidity zone of the territory, we determine the operating conditions of the enclosing structures - group A.
The climatic characteristics required for calculations for the city of Izhevsk from SNiP 2.01.01-82 are presented below in tabular form.
Temperature and water vapor pressure of outside air
| Izhevsk | Average by month | |||||||||||
| I | II | III | IV | V | VI | VII | VIII | IX | X | XI | XII | |
| -14,2 | -13,5 | -7,3 | 2,8 | 11,1 | 16,8 | 18,7 | 16,5 | 10 | 2,3 | -5,6 | -12,3 | |
| Average annual | 2,1 | |||||||||||
| Absolute minimum | -46,0 | |||||||||||
| Absolute maximum | 37,0 | |||||||||||
| Average maximum of the hottest month | 24,3 | |||||||||||
| The coldest day with a probability of 0.92 | -38,0 | |||||||||||
| The coldest five-day period with a security of 0.92 | -34,0 | |||||||||||
| <8
° C, days. average temperature |
223 -6,0 |
|||||||||||
| Length of period with average daily temperature<10
° C, days. average temperature |
240 -5,0 |
|||||||||||
| Average temperature of the coldest period of the year | -19,0 | |||||||||||
| Length of period with average daily temperature£ 0 ° C day. | 164 | |||||||||||
| Water vapor pressure of outdoor air by month, hPa | I | II | III | IV | V | VI | VII | VIII | IX | X | XI | XII | ||||
| 2,2 | 2,2 | 3 | 5,8 | 8,1 | 11,7 | 14,4 | 13,2 | 9,5 | 6,2 | 3,9 | 2,6 | |||||
| Average monthly relative air humidity, % |
Coldest month |
85 | ||||||||||||||
| Hottest month | 53 | |||||||||||||||
| Precipitation amount, mm | In a year | 595 | ||||||||||||||
| Liquid and mixed per year | — | |||||||||||||||
| Daily maximum | 61 | |||||||||||||||
When performing technical calculations of insulation, it is not recommended to determine the total reduced heat transfer resistance of the outer fence as the sum of the reduced heat transfer resistance of the existing wall and additionally installed insulation. This is due to the fact that the influence of existing heat-conducting inclusions changes significantly in comparison with what was initially calculated.
Reduced resistance to heat transfer of enclosing structures R(0)
should be taken in accordance with the design assignment, but not less than the required values determined on the basis of sanitary, hygienic and comfortable conditions adopted at the second stage of energy saving. Let us determine the GSOP indicator (degree-day heating season):
GSOP = (t in – t from.trans.)
´ z from.trans. ,
Where t in
– design temperature of internal air,°
C, accepted according to SNiP 2.08.01-89;
t from.lane, z from.lane
. – average temperature,
°
C and - duration of the period with an average daily air temperature below or equal to 8° From day.
From here GSOP
= (20-(-6))
´ 223 = 5798.
Fragment of table 1b*(K) SNiP II-3-79*
| Buildings and premises |
GSOP* | Reduced heat transfer resistance enclosing structures, not less than R (o)tr, m 2 ´° C/W |
||
| walls | attic floors | windows and balcony doors | ||
| Residential, therapeutic preventive and children's institutions, schools, boarding schools |
2000 4000 6000 8000 |
2,1 2,8 3,5 4,2 |
2,8 3,7 4,6 5,5 |
0,3 0,45 0,6 0,7 |
| * Intermediate values are determined by interpolation. | ||||
Using the interpolation method, we determine the minimum value R(o)tr
,: for walls - 3.44 m 2
´°
C/W; for attic floors - 4.53 m 2
´°
C/W; for windows and balcony doors - 0.58 m 2
´°
WITH
/W
Calculation insulation and thermal characteristics of a brick wall
is made on the basis of preliminary calculations and justification of the accepted thickness insulation.
Thermal characteristics of wall materials
| Layer No. (counting from the inside) |
Item No. according to Appendix 3 SNiP II-3-79* |
Material | Thickness, d m |
Density r, kg/m 3 |
Heat capacity s, kJ/(kg°C) |
Thermal conductivity l , W /(m°C) |
Heat absorption s, W/ (m^C) |
Vapor permeability m mg/(mhPa) |
|
| Fencing – external brick wall | |||||||||
| 1 | 71 |
Cement-sand mortar |
0.02 | 1800 | 0,84 | 0,76 | 9,60 | 0,09 | |
| 2 | 87 | 0,64 | 1800 | 0,88 | 0,76 | 9,77 | 0,11 | ||
| 3 | 133 | Brand P175 | x/span | 175 | 0,84 | 0,043 | 1,02 | 0,54 | |
| 4 | 71 | 0,004 | 1500 | 0,84 | 0,76 | 9,60 | 0,09 | ||
Where X– unknown thickness of the insulation layer.
Let us determine the required heat transfer resistance of enclosing structures:R o tr,
setting:
n — coefficient taken depending on the position of the outer
Surfaces of enclosing structures in relation to outside air;
t in— design temperature of internal air, °C, taken according toGOST 12.1.005-88 and design standards for residential buildings;
t n— estimated winter outside air temperature, °C, equal to the average temperature of the coldest five-day period with a probability of 0.92;
D
t n- standard temperature difference between the internal air temperature
And the temperature of the inner surface of the enclosing structure;
a
V
From here R o tr = = 1.552
Since the selection condition R o tr
is the maximum value from the calculation or table value, we finally accept the table value R o tr = 3.44.
The thermal resistance of a building envelope with successively arranged homogeneous layers should be determined as the sum of the thermal resistances of the individual layers. To determine the thickness of the insulating layer, we use the formula:
R o tr ≤ + S + ,
Where a
V— heat transfer coefficient of the inner surface of enclosing structures;
d
i
- layer thickness, m;
l
i
— calculated thermal conductivity coefficient of the layer material, W/(m °C);
a
n— heat transfer coefficient (for winter conditions) the outer surface of the enclosing structure, W/(m2
´
°C).
Of course, the importance X should be minimal to save money, so the necessary
the value of the insulating layer can be expressed from the previous conditions, resulting in X
³
0.102 m.
We take the thickness of the mineral wool board equal to 100 mm, which is a multiple of the thickness of manufactured products of the P175 brand (50, 100 mm).
Determining the actual value R o f
= 3,38 ,
this is 1.7% less R o tr
= 3.44, i.e. fits into permissible negative deviation
5% .
The above calculation is standard and is described in detail in SNiP II-3-79*. A similar technique was used by the authors of the Izhevsk program for the reconstruction of buildings of the 1-335 series. When insulating a panel building that has a lower initial R o
, they adopted foam glass insulation produced by Gomelsteklo JSC according to TU 21 BSSR 290-87 with a thicknessd
= 200 mm and thermal conductivity coefficientl
= 0.085. The additional heat transfer resistance obtained in this case is expressed as follows:
R add =
= = 2.35, which corresponds to the heat transfer resistance of a 100mm thick insulating layer made of mineral wool insulation R=2.33
accurate to (-0.86%). Taking into account the higher initial characteristics of brickwork with a thickness of 640 mm In comparison with the building wall panel of the 1-335 series, we can conclude that the total heat transfer resistance we obtained is higher and meets the requirements of SNiP.
Numerous recommendations of TsNIIP ZHILISHCHE provide a more complex version of the calculation with dividing the wall into sections with different thermal resistances, for example, in places where floor slabs support, window lintels. For a building of series 1-447, up to 17 sections are introduced on the calculated wall area, limited by the floor height and the repetition distance of the facade elements that affect the heat transfer conditions (6 m). SNiP II-3-79* and other recommendations do not provide such data
In this case, the coefficient of thermal heterogeneity is introduced into the calculations for each section, which takes into account the losses of walls that are not parallel to the heat flow vector in places where window and doorways, as well as the impact on losses of neighboring areas with lower thermal resistance. According to these calculations, for our zone we would have to use a similar mineral wool insulation thickness of at least 120mm. This means that, taking into account the multiple sizes of mineral wool slabs with the required average density r > 145 kg/m 3 (100, 50 mm), according to TU 5762-001-36736917-98, the introduction of an insulating layer consisting of 2 slabs 100 and 50 mm thick will be required. This will not only double the cost of thermal remediation, but will also complicate the technology.
Compensate for possible minimal discrepancies in thermal insulation thickness when complex scheme calculations can be made using minor internal measures to reduce heat losses. These include: rational selection of window filling elements, high-quality sealing of window and door openings, installation of reflective screens with a heat-reflecting layer applied behind the heating radiator, etc. The construction of heated areas in the attic also does not entail an increase in overall (existing before reconstruction) energy consumption, since, according to manufacturers and organizations that carry out insulation of facades, heating costs are even reduced by 1.8 to 2.5 times.
Calculation of thermal inertia of an external wall
start with a definition thermal inertia D
enclosing structure:
D = R 1
´ S 1 + R 2 ´ S 2 + … +R n ´Sn,
Where R
– heat transfer resistance of the i-th layer of the wall
S
- heat absorption W/(m
´°
WITH),
from here D
= 0,026
´ 9.60 + 0.842 ´ 9.77 + 2.32 ´ 1.02 + 0.007 ´ 9,60 = 10,91.
Calculation heat storage capacity of the wall Q carried out in order to prevent too rapid and excessive heating and cooling of interior spaces.
There are internal heat storage capacity Q in
(if there is a temperature difference from inside to outside - in winter) and outside Q n
(if there is a temperature difference from outside to inside - in summer). Internal heat storage capacity characterizes the behavior of a wall during temperature fluctuations on its internal side (heating is turned off), external - on the external side ( solar radiation). The greater the heat-storing capacity of the fences, the better the indoor microclimate. Large internal heat storage capacity means the following: when the heating is turned off (for example, at night or during an accident), the temperature of the internal surface of the structure decreases slowly and for a long time it gives off heat to the cooled air of the room. This is the advantage of a design with a large Q c.
The disadvantage is that when the heating is turned on, this design takes a long time to warm up. The internal heat storage capacity increases with increasing density of the fencing material. Lightweight thermal insulation layers of the structure should be placed closer to the outer surface. Placing thermal insulation from the inside leads to a decrease in Q
V. Fencing with small Q in
They warm up quickly and cool down quickly, so it is advisable to use such structures in rooms with short-term occupancy. Total heat storage capacity Q = Q in + Q n.
When assessing alternative options fencing, preference should be given to structures with b O
greater Q
V.
Calculates heat flux density calculate
q = = 15.98
.
Inner surface temperature:
t in = t in – , t in = 20 – = 18.16 ° WITH.
External surface temperature:
t
n = t n + ,
t
n = -34 + = -33,31
°
WITH.
Temperature between layers i and layer i+1(layers – from inside to outside):
t i+1 = t i — q ´ R i ,
Where R i
– heat transfer resistance i– th layer, R i = .
The internal heat storage capacity will be expressed:
Q in =
S
with i
´r
i
´d
i
´
(
t
iср - tн),
Where with i
– heat capacity of the i-th layer, kJ/(kg
´ °С)
r
i
– layer density according to table 1, kg/m 3
d
i
– layer thickness, m
t
i avg
- average layer temperature,°
WITH
t n
– estimated outside air temperature,°
WITH
Q in
= 0.84 ´ 1800 ´ 0.02 ´ (17.95-(-34)) + 0.88 ´ 1800 ´ 0.64 ´ (11.01-(-34))
0.84 ´ 175 m
l,
°C
t i avg
°C
Brand P-175
According to the calculation results in t-coordinates d The temperature field of the wall is constructed in the temperature range t n -t c.
Vertical scale 1mm = 1°C
Horizontal scale, mm 1/10
Calculation thermal resistance of the wall according to SNiP II-3-79* is carried out for areas with an average monthly temperature of July 21°
C and above. For Izhevsk, this calculation will be unnecessary, since the average temperature in July is 18.7° C.
Check external wall surfaces for moisture condensation performed subject tot
V< t р,
those. in the case where the surface temperature is below the dew point temperature, or when the water vapor pressure calculated from the wall surface temperature is greater than the maximum water vapor pressure determined from the internal air temperature
(e in >E t
). In these cases, moisture may precipitate from the air on the wall surface.
| Estimated air temperature in the room t in according to SNiP 2.08.01-89 | 20°C |  |
| relative humidity room air |
55% | |
| Temperature of the inner surface of the enclosing structure t in |
18.16°C | |
| Dew point temperature t p, determined by id diagram |
9.5°C | |
| Possibility of moisture condensation on the wall surface | No | Dew point temperature t r
determined by i-d diagram. |
Examination Possibility of condensation in outer corners rooms is complicated by the fact that it requires knowing the temperature of the inner surface in the corners. When using multi-layer fencing structures, the exact solution to this problem is very difficult. But with enough high temperature surface of the main wall, it is unlikely that it will decrease in the corners below the dew point, that is, from 18.16 to 9.5
°
WITH.
Due to the difference in partial pressures (water vapor elasticity) in air environments separated by a fence, a diffusion flow of water vapor occurs with an intensity of - g
from an environment with high partial pressure to an environment with lower pressure (for winter conditions: from inside to outside). In the section where warm air suddenly cools on contact with a cold surface to a temperature ≤ t r moisture condensation occurs. Determination of the zone of possibility moisture condensation in the thickness fencing is carried out if the options specified in clause 6.4 of SNiP II-3-79* are not met:
a) Homogeneous (single-layer) external walls of rooms with dry or normal conditions;
b) Two-layer external walls of rooms with dry and normal conditions, if inner layer the wall has a vapor permeation resistance of more than 1.6 Pa´ m 2 ´ h / mg
Vapor permeation resistance is determined by the formula:
R p = R pv + S Rpi
Where R pv
– resistance to vapor permeation of the boundary layer;
Rpi
– layer resistance, determined in accordance with clause 6.3 of SNiP II-3-79*: Rpi = ,
Where
d
i,
m
i- respectively, the thickness and standard resistance to vapor permeation of the i-th layer.
From here
R p
= 0,0233 + + = 6,06
.
The resulting value is 3.8 times higher minimum required that already guarantees against moisture condensation in the thickness of the wall.
 |
 |
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For residential buildings mass series in the former The GDR has developed standard parts and components for both pitched roofs and buildings with roofless roofing, with base part different heights. After replacing the window fillings and plastering the facade, the buildings look much better.
From a thermal engineering point of view, there are three types of external walls based on the number of main layers: single-layer, two-layer and three-layer.
Single-layer walls are made of structural and thermal insulation materials and products that combine load-bearing and heat-protective functions.
In three-layer fences with protective layers on point (flexible, keyed) connections, it is recommended to use insulation made of mineral wool, glass wool or expanded polystyrene with a thickness determined by calculation taking into account heat-conducting inclusions from the connections. In these fences, the ratio of the thicknesses of the outer and inner layers must be at least 1:1.25 at minimum thickness outer layer 50 mm.
In double-layer walls, it is preferable to place the insulation on the outside. Two options for external insulation are used: systems with an outer covering layer without a gap and systems with an air gap between the outer facing layer and the insulation. It is not recommended to use thermal insulation on the inside due to the possible accumulation of moisture in the thermal insulation layer, however, if such use is necessary, the surface on the room side must have a continuous and durable vapor barrier layer.
When designing walls made of brick and other small-piece materials, lightweight structures should be used as much as possible in combination with slabs made of effective thermal insulation materials.
The course project assumes a load-bearing wall of a three-layer structure with a load-bearing layer of solid ceramic brick 380 mm thick, concrete blocks or reinforced concrete (with a layer of internal plaster 20 mm), a layer of thermal insulation and a protective and decorative outer layer of brick 120 mm thick or lime-cement plaster thickness 25 – 30 mm (Fig. 3.1). The coefficient of thermal uniformity without taking into account the slopes of openings and other heat-conducting inclusions is 0.95.
For the protective wall, ceramic face bricks or stones (GOST 7484-78) or selected standard ones (GOST 530-95), preferably semi-dry pressing, as well as sand-lime brick (GOST 379-95) can be used. When facing sand-lime brick the base, belts, parapets and cornice are made of ceramic bricks.
When facing, the brickwork is reinforced with the load-bearing part of the wall with welded reinforcing mesh, placed in height increments of 600 mm.
With a finishing layer of traditional thick-layer plaster 25 - 30 mm thick thermal insulation boards They are attached to the load-bearing layer of the wall using glue and additionally with spacer dowels.
External plaster is made from lime-cement mortar, prepared on site from lime, sand, cement, water and additives, or from ready-made mortar mixtures, and is reinforced with galvanized steel mesh in accordance with GOST 2715-75 with a mesh size of 20 mm and a wire diameter of 1 - 1.6 mm.
The reduced heat transfer resistance, m °C/W, for external walls should be determined in accordance with SNiP 23-02 for the facade of a building or for one intermediate floor, taking into account the slopes of the openings without taking into account their fillings, checking the condition of non-precipitation of condensation in areas in areas of heat-conducting inclusions.
Required thickness The thermal insulation layer should be determined taking into account the coefficient of thermal uniformity.
Thermal uniformity coefficient taking into account the thermal uniformity of window slopes and adjacent internal fences of the designed structure for:
Industrially manufactured panels should, as a rule, be no less than the values established in the table. 6;
For brick walls of residential buildings, as a rule, it should be at least 0.74 with a wall thickness of 510 mm,
0.69 - with a wall thickness of 640 mm and 0.64 - with a wall thickness of 780 mm.
Table 6
Minimum valid values thermal homogeneity coefficient for industrially manufactured structures
Rice. 3.1. Structural solutions for external walls
1 – wall (load-bearing part); 2 – protective and decorative masonry; 3 – straightening gap; 4 – thermal insulation; 5 - interior plaster; 6 – external plaster; 7 – welded galvanized metal grid 20x20 Ø 1.0 – 1.6; 8 – adhesive composition for gluing thermal insulation boards; 9 – leveling plaster; 10 – embedded mesh; 11 - dowel
Example 1.
Perform thermal engineering calculations of the external wall administrative building in St. Petersburg. The design of the outer wall is shown in Fig. 3.2.
Rice. 3.2. Calculation diagram of the outer wall
1 – cement-lime plaster; 2; 4 – brickwork; 3 – mineral wool plate “CAVITI BATTS”
Solution.
1. We determine the necessary initial data for thermal engineering calculations:
- calculated average temperature of the internal air of the building for thermal engineering calculations of enclosing structures - ˚С - the minimum value of the optimal temperature for premises of category 2;
Average outside air temperature during the heating period - °C - table. 1 SNiP 23-01-99;
Duration of the heating period - days - table. 1 SNiP 23-01-99;
Humidity conditions in the building premises – normal – table. 1 SNiP 23-02-2003;
Humidity zone for St. Petersburg - humid - adj. In SNiP 02/23/2003;
Operating conditions of enclosing structures – B – table. 2 SNiP 02/23/2003.
2. The normalized (required) reduced resistance to heat transfer of the fence structure is taken according to table. 7 depending on the number of degree days of the heating period or calculated according to
, m 2 o C/W, (2)
where and are the values determined from the table. 8;
– degree-day of the heating period, o C day, determined by the formula
, about S day, (3)
here is the estimated average temperature of the building’s internal air, ˚С;
The required heat transfer resistance of the wall is a function of the number of degree days of the heating period ( GSOP):
GSOP=D=(t in - t from. Lane) · Z from. lane ;
Where: t in– design temperature of internal air, o C;
t in= 20 o C – for premises of category 3a according to GOST 30494-96;
t from.lane, Z from.lane– average temperature, o C and duration, days. period with an average daily air temperature below or equal to 8 o C according to SNiP 23-01-99* “Building climatology”.
For St. Petersburg:
D= ·220=4796;
R tr =a·D+b=0.0003·4796+1.2=2.639 (m 2 o C)/W.
The thickness of the thermal insulation layer at l B= 0.044 W/(m o C) and the coefficient of thermal uniformity r = 0.92 will be:
We take the insulation layer to be 80 mm, then the actual heat transfer resistance will be:
1. The construction project is a 16-story, single-section, large-panel residential building, built in the city of Kashira, Moscow region. Operating conditions for fences B according to SNiP 23-02.
2. External walls - made of three-layer reinforced concrete panels on flexible connections with polystyrene foam insulation 165 mm thick. The panels have a thickness of 335 mm. Along the perimeter of the panels and their openings, the insulation has protective layer from cement-sand mortar 10 mm thick. To connect reinforced concrete layers, two types of flexible connections made of corrosion-resistant steel with a diameter of 8 mm are used: triangular and point (studs). The calculation of the reduced heat transfer resistance was carried out according to formula (14) and the corresponding example of calculation in Appendix N.
3. To fill the openings, wooden window blocks with triple glazing in separate-paired frames.
4. Mineral wool insulation is used in the joints, sealed on the outside with Vilaterm sealant.
5. For the Moscow region (Kashira), according to SNiP 23-01, the average temperature and duration of the heating period are: . Internal air temperature =20 °C. Then the degree-days of the heating period according to formula (1) are
=(20+3.4) 212=4961 °C day.
Calculation procedure
1. According to Table 4 SNiP 23-02 =4961 °C day corresponds to the normalized heat transfer resistance for the walls of residential buildings.
2. The resistance to heat transfer of panels along the surface, calculated using formula (8), is equal to
3. The number of heat-conducting inclusions and thermal inhomogeneities in the walls of a 16-story building panel house These include flexible connections, window slopes, horizontal and vertical joints of panels, corner joints, junction of panels to the cornice and basement floor.
To calculate the coefficients of thermal uniformity using formula (14) various types panels, the influence coefficients of heat-conducting inclusions and the areas of their influence zones are calculated based on solving problems of stationary thermal conductivity on the computer of the corresponding units and are given in
table K.1.
Table K.1
For the first floor
0.78·0.962=0.75;
For the last floor
0.78·0.97=0.757.
Reduced coefficient of thermal uniformity of the building façade
16/(14/0,78+1/0,75+1/0,757)=0,777.
The reduced resistance to heat transfer of the facade of a 16-story residential building according to formula (23) is equal to
Consequently, the external walls of a 16-story residential building meet the requirements of SNiP 23-02.
The share of wall materials in the price of a country property is 3-10%. At the same time, the influence of wall material on living comfort remains high. Even the colloquial name of a house is determined by the design of its walls.
Comfort in a home depends not only on what the walls are made of. There are a lot of factors influencing comfort. But the choice of wall material determines the basic characteristics of the house, which will remain with it forever and will not go away either when the heating system is replaced or when the roof is repaired. Even the verbal definition of home is based on choice wall material: stone, wooden, frame. The design of the wall seems to be a fundamental characteristic of the building, even at the everyday level.
This article will not say a word about the advantages and disadvantages of various materials from the point of view of environmental friendliness, durability or impact on the indoor microclimate. These issues deserve separate consideration. Our article is devoted to another aspect of choice: the likelihood of hidden defects. We will talk about how realistic it is to achieve those characteristics that are declared by manufacturers and used in calculations by designers, heating engineers and other specialists.
In general, a wall is:
- Structural solution of the wall (load-bearing, heat-insulating, steam-windproof, finishing, etc. layers);
- Constructive solution of its individual components (installation diagram of windows and doors, connection of floors, roofs, partitions, laying of communications and other inhomogeneities);
- Actual implementation of adopted design decisions.
Feasibility of design solutions
There are no formal criteria for reliability and feasibility. We cannot assess resistance to defects based on standards. Therefore, we will determine the feasibility of design solutions based on common sense considerations.
Resistance to defects consists of two components:
- It is fundamentally possible to allow accidental defects during conscientious work;
- Possibility to check quality finished wall without disassembly, without the use of complex equipment and at any time of the year.
Both of these components are equally important when choosing a structural solution for a wall. And depending on whether construction is carried out with your own hands or with the involvement of contractors, the emphasis when choosing a wall structure may shift from the likelihood of an accidental defect to the possibility visual assessment quality of work already completed.
Brief classification of external walls
1. Supporting frame with filling. Example: load-bearing frame - boards or metal profile, cladding and filling (in layers from the inside out) - gypsum fiber board (gypsum plasterboard, OSB), plastic film, insulation, wind protection, cladding.
2. Load-bearing wall with external insulation with separation of load-bearing and heat-insulating functions between layers. Example: a wall made of brick, stones or blocks with external insulation (expanded polystyrene or mineral wool board) and cladding (face brick, plaster, curtain wall with an air gap).
3. Single layer wall made of material that performs both load-bearing and heat-insulating functions. Example: a log wall without finishing or a plastered brick wall.
4. Exotic systems with permanent formwork we will remove from consideration due to its low prevalence.
Let's try to understand at what stages of construction work deviations from design decisions and the occurrence of defects are possible.
Frame structures
When mentioned frame buildings there is no need to give the palm of their invention to Canada. Panel houses appeared here long before the fall " iron curtain" Therefore, it is quite possible for us to evaluate their reliability. Construction: vertical and horizontal load-bearing elements of the frame, braces or sheet cladding that impart rigidity to the structure.
There are no questions about the feasibility of the framework itself - assembled frame allows you to evaluate your quality using the simplest means. Visual evenness and verifiable rigidity when applying horizontal loads are sufficient for acceptance of the frame into operation. Another thing is the layers designed to provide thermal protection.
Insulation. Must tightly fill all cavities formed by power elements. A task that is difficult to implement when the pitch between the frame elements differs from the dimensions of the slab insulation. And it is almost impossible to implement in the presence of diagonal braces in the frame structure (of course, there are both fill-in and fill-in insulation that are free of these disadvantages - here we are talking about the most popular filling options).
Vapor barrier. A layer of film with high resistance to vapor permeation. Must be installed with joints sealed, without weakening by perforation from mechanical elements fastenings, with particularly careful execution around window and door openings, as well as in places where communications exit from the wall, hidden in the thickness of the insulation, electrical and other wiring, etc. In theory, a vapor barrier can be done soundly and carefully. But if you are a customer receiving a finished structure, the quality of the vapor barrier of a wall already sheathed from the inside cannot be checked.
Walls with external insulation
A constructive solution that has spread over the past twenty years, along with the tightening regulatory requirements̆ to thermal protection and rising energy prices. The two most common options are:
- load-bearing stone wall (200–300 mm) + insulation + cladding of 1⁄2 bricks (120 mm);
- load-bearing stone wall (200–300 mm) + insulation glued and secured with dowels + reinforced plaster by insulation or air gap, wind protection and sheet cladding.
There are practically no questions about the load-bearing layer of the wall. If the wall is built fairly evenly (without obvious deviations from the vertical), its load-bearing capacity will almost always be sufficient to fulfill its main – load-bearing – function. (In low-rise construction, the strength characteristics of wall materials are rarely fully used.)
Insulation. Glued to a load-bearing wall, mechanically attached to it, covered with a layer of reinforced plaster, it does not raise any questions. You can make a mistake in choosing glue, dowels, or plaster composition - then after some time the layer of thermal insulation or finishing will begin to lag behind the wall. In general, the quality is checked by means of visual control, and emerging defects are obvious.
The quality of work with a curtain wall with an air gap is no longer so obvious. To check the tightness of the insulation installation, it is necessary to dismantle the cladding; installation of wind protection also requires intermediate acceptance.
When facing the insulation with brick, the quality of its installation cannot be checked even with a thermal imager. And the defect can be eliminated only after dismantling the cladding (read: demolishing the brick wall).
Single-layer walls
A wall made of logs or beams, built using high-quality inter-crown sealant and not sheathed with anything, is verified for compliance with the project by simple inspection. Wood cracking, which reduces the reduced thickness of the log by 40-60%, and shrinkage of 6-8%, we will not consider here.
Hollow stones. These include empty concrete blocks and multi-hollow large-format ceramics. Hollow blocks made of heavy concrete will not provide the required thermal resistance, and therefore can only act as part of the wall from the previous section. A single-layer wall made of large-format ceramics, plastered on both sides, is guaranteed to be protected from blowing. Its thin places: corners other than 90° and masonry seams.
Processing fragile multi-slot blocks to create a non-right angle leads to the formation of an openwork joining surface and a thick vertical mortar joint. But horizontal masonry joints have a much greater influence on the deviation of the wall from the design characteristics. Firstly, in themselves they are already bridges of cold. Secondly, according to the rules, in order to avoid filling the voids with mortar, a fiberglass mesh with a cell of 5x5 mm should be rolled out on top of the stone before laying the mortar. In this case, the mobility of the solution should be carefully controlled to prevent it from flowing through the mesh cells.
Thus, the occurrence of accidental defects is possible even with conscientious work performed. When carrying out work by a contractor, there is no opportunity to assess the quality of the masonry without the use of a thermal imager.
Solid stones. These include wall blocks made of cellular or lightweight concrete and solid brick. The quality of a wall made of solid brick can be assessed from afar with the naked eye, so there is no need to talk about hidden defects in relation to such masonry. The disadvantage of solid brick, as well as stones made of high-density concrete, is its relatively high thermal conductivity. Such walls require additional thermal insulation, which brings us back to the previous section, to walls with external insulation.
What remains are cellular concrete blocks. With a density of more than 500 kg/m3, as well as when using conventional cement-sand mortar with a joint thickness of more than 10 mm, it becomes advisable to additionally insulate the wall, which deprives its structure graceful simplicity. And only cellular concrete with a density of up to 500 kg/m3, with high geometric precision of the blocks, allowing masonry to be carried out using thin-layer mortar, gives us a structure so simple that the occurrence of hidden defects in it is simply impossible.
Single-layer wall made of low-density cellular concrete with adhesive joints 1-3mm thick.
It's not easy to spoil it. For example, the blocks can be stacked dry, without any fastening to each other, just like children's blocks. If such a wall is then plastered on both sides using a grid, it will perform all the tasks assigned to it 100%. The thermal protection of a dry-folded (and plastered on both sides) structure will not decrease, but will even increase somewhat due to the absence of heat-conducting mortar layers. At the same time, the ability to absorb vertical loads, the overall rigidity and stability of such a wall in the presence of a strapping belt at the floor level will not differ from the calculated ones.
Accuracy geometric dimensions, the large format of the blocks and thin-layer adhesive make it fundamentally impossible to lay the masonry with noticeable deviations from the vertical or any irregularities. The masonry automatically turns out smooth even for an inexperienced mason. Angles other than 90 ̊ are made using conventional hand hacksaw. Preparation for finishing is done by simply filling the seams, i.e. just as easy as before finishing a plasterboard surface.
In terms of protection from hidden defects, a single-layer wall has no equal. In terms of protection from defects in general, both hidden and obvious, there is no equal to a single-layer wall made of cellular concrete blocks with a density of up to 500 kg/m3. Only such a wall, made in the material, is guaranteed to correspond to the adopted design decision.
Table 3.2 shows a diagram showing the dependence and variability of design solutions and methods for reconstructing old housing stock. In the practice of reconstruction work, which takes into account the physical wear and tear of non-replaceable structures, several solutions are used: without changing design diagram and with its change; without changing the building volume, with the addition of floors and small extensions.
Table 3.2
The first option involves restoring the building without changing the building volume, but with the replacement of floors, roofing and other structural elements. At the same time, a new layout is created that meets modern requirements and demands. social groups residents. The reconstructed building must preserve the architectural appearance of the facades, and its operational characteristics must be brought up to modern regulatory requirements.
Options with changes in design schemes provide for an increase in the construction volume of buildings by: adding volumes and expanding the building without changing its height; superstructures without changing the plan dimensions; extensions of several floors, extensions of additional volumes with changes in the dimensions of the building in plan. This form of reconstruction is accompanied by redevelopment of premises.
Depending on the location of the building and its role in the development, the following reconstruction options are carried out: with preservation of residential functions; with partial repurposing and complete repurposing of the building's functions.
Reconstruction of residential buildings should be carried out comprehensively, including, along with the reconstruction of the intra-block environment, its landscaping, improvement and restoration of utility networks, etc. During the reconstruction process, the range of built-in premises is revised in accordance with the standards for the provision of primary care institutions to the population.
In the central areas of cities, buildings being reconstructed may house built-in citywide and commercial establishments for periodic and permanent services. The use of built-in spaces transforms residential buildings into multifunctional buildings. Non-residential premises are located on the first floors of houses located along the red building lines.
In Fig. 3.5 shows structural and technological options for the reconstruction of buildings with preservation ( A) and with change ( b,V) design schemes, without changing volumes and with their increase (superstructure, extension and expansion of the planned dimensions of buildings).
Rice. 3.5. Reconstruction options for early residential buildings A- without changing the design scheme and construction volume; b- with the addition of small volumes and the transformation of the attic floor into an attic; V- with the addition of floors and extension of volumes; G- with an extension of the building to the end of the building; d, f- with the construction of buildings; and- with extension of volumes of curvilinear shapes
A special place in the reconstruction of urban centers should be given to the rational development of underground space adjacent to buildings, which can be used as shopping centers, parking lots, small businesses, etc.
The main constructive and technological method for reconstructing buildings without changing the design scheme is to preserve the permanent structures of the external and internal walls, stairwells with the installation of heavy-duty floors. If there is a significant degree of wear and tear on the internal walls as a result of frequent redevelopment with the construction of additional openings, relocation of ventilation ducts, etc. reconstruction is carried out by installing built-in systems while preserving only the external walls as load-bearing and enclosing structures.
Reconstruction with a change in the building volume involves the installation of built-in permanent systems with independent foundations. This circumstance makes it possible to add several floors to buildings. In this case, the structures of external and, in some cases, internal walls are freed from the loads of the overlying floors and turned into self-supporting enclosing elements.
When reconstructing with the widening of a building, constructive and technological options are possible for partially using existing foundations and walls as load-bearing ones with redistribution of loads from the floors being built on to the external elements of buildings.
The principles of reconstruction of buildings built later (1930-40s) are dictated by the simpler configuration of sectional type houses, the presence of floors made of small-piece reinforced concrete slabs or wooden beams, as well as the smaller thickness of external walls. The main methods of reconstruction consist in the addition of elevator shafts and other small volumes in the form of bay windows and inserts, the addition of floors and attics, and the construction of remote low-rise extensions for administrative, commercial or household purposes.
Increasing the comfort of apartments is achieved through complete redevelopment with replacement of floors, and an increase in the volume of the building as a result of the superstructure ensures an increase in the building density of the quarter.
The most typical methods of building reconstruction of this type are the replacement of floors with prefabricated or monolithic structures with a complete redevelopment, as well as an additional superstructure of 1-2 floors. In this case, the superstructure of buildings is carried out in cases where the condition of the foundations and wall fencing ensures the perception of changed loads. As experience has shown, buildings of this period allow for the addition of up to two floors without strengthening the foundations and walls.
In case of increasing the height of the superstructure, built-in building systems of prefabricated, prefabricated and monolithic structures are used.
The use of built-in systems makes it possible to implement the principle of creating large overlapping areas that facilitate the implementation of flexible room layouts.