Thermal conductivity of roofing material. Comparison of the thermal conductivity of various building materials and the calculation of the wall thickness

The issue of insulation of apartments and houses is very important - the constantly rising cost of energy carriers obliges to take care of heat in the room. But how to choose the right insulation material and calculate its optimal thickness? To do this, you need to know the heat conductivity.

What is heat conduction?

This value characterizes the ability to conduct heat inside the material. Those. determines the ratio of the amount of energy passing through a body of 1 m² and a thickness of 1 m per unit time - λ (W / m * K). Simply put - how much heat will be transferred from one surface of the material to another.

As an example, consider an ordinary brick wall.

As can be seen in the figure, the room temperature is 20 ° C, and on the street - 10 ° C. To comply with this regime in the room, it is necessary that the material from which the wall is made, with a minimum coefficient of thermal conductivity. It is under this condition that we can talk about effective energy saving.

For each material there is a specific indicator of this quantity.

At construction the following division of materials is accepted, which perform a certain function:

• The erection of the main frame of buildings - walls, partitions, etc. For this, concrete, brick, aerated concrete, etc. are used.

Their thermal conductivity values ​​are quite large, which means that to achieve good energy conservation it is necessary to increase the thickness of the external walls. But this is not practical, since it requires additional costs and an increase in the weight of the entire building. Therefore, it is customary to use special additional insulating materials.

• Heaters. These include, polystyrene, expanded polystyrene and any other material with a low coefficient of thermal conductivity.

They provide proper protection of the house from the rapid loss of thermal energy.

In construction, the requirements for the main materials are mechanical strength, reduced hygroscopicity index (moisture resistance), and least of all - their energy characteristics. Therefore, special attention is paid to thermal insulation materials, which must compensate for this "lack".

However, the application of the value of thermal conductivity in practice is difficult, since it does not take into account the thickness of the material. Therefore, the opposite concept is used: the coefficient of heat transfer resistance.

This value is the ratio of the material thickness to its thermal conductivity coefficient.

The value of this parameter for residential buildings is prescribed in SNiP II-3-79 and SNiP 23-02-2003. According to these normative documents, the coefficient of heat transfer resistance in different regions of Russia should not be less than those indicated in the table.

This calculation procedure is necessary not only when planning the construction of a new building, but also for the competent and effective insulation of the walls of the already erected house.

Thermal conductivity of the materials from which the building is built is an important indicator, on the value of which depends on how well the heat in your house will be saved. Especially it is worth paying attention to the heat-insulating properties of products used for the erection of external walls, since they protect the interior of the structure from heat loss in winter. Than this indicator is lower, the longer the heat is stored, and, consequently, the costs for heating the housing are reduced.

  Heat conduction table

Thermal conductivity is the ability of matter to conduct heat and take the temperature of its surrounding objects. The unit of measurement of the coefficient of heat index is the value W / (mK). The table below shows the thermal conductivity of the main wall materials, which are most often used in the construction and insulation of facade walls.

The coefficient of any magnitude can be influenced by the humidity of the air, since its values, although insignificantly, vary with the season and climatic conditions. Where the density of the material is not indicated in the table, the value is not decisive in terms of heat conduction.

The thermal conductivity of a material is determined by its chemical composition, degree and nature of porosity, as well as by the conditions under which heat transfer takes place by humidity and air temperature. Materials having a fibrous and layered structure of the structure can conduct heat differently. For example, wood products with a cross section of fibers have a greater degree of thermal conductivity than with a longitudinal section.

Since air transmits very little heat (0.023W / m-0 C), porous materials with air cells have less thermal insulation properties. But if the product is saturated with moisture, its thermal conductivity increases, because water conducts heat faster than air, 25 times.

  Comparative characteristics

Based on the data in the table, taken from the SNIP from 2003, porous wall materials, such as foam concrete and aerated concrete (see) based on lime and arbolite, have the least thermal conductivity. But the cellular structure has a big drawback: pores are quickly saturated with moisture from the environment, as a result of which their thermal conductivity increases.

In addition, after being absorbed by moisture, after several cycles of freezing and thawing, the porous structures begin to lose their strength, which leads to the destruction of the material. To maintain the frost-resistance of aerated concrete and foam blocks, use a moisture-resistant finish for outdoor work.

The walls of the house made of brick masonry have a greater thermal conductivity, so for better heat saving their thickness should be about 40 or even 50 cm. Such consumption leads to a rise in the cost of the structure, so in recent times, brick is increasingly being used as facing material.

They are lined with walls from light blocks, protecting them from the destructive effects of moisture. In addition, the brick house looks beautiful and does not require additional finishing. If desired, between the masonry and concrete blocks, a heater is attached, which increases the safety of heat in the house.

  Types of heaters

Of insulation with a lower thermal conductivity have expanded polystyrene and extruded polyurethane foam. These are hard, brittle materials, produced in plates, and having a cellular structure. But it must be taken into account that as the density of the material structure increases, its ability to transmit heat also increases.

Mineral heaters in addition to good heat preservation, have excellent sound insulation properties: they extinguish sounds, not allowing them to enter the room.

Minvate is produced in the form of plates or in rolls. Plates are encased walls, roof, floor. The roll insulation is suitable for sheltering water supply and heating pipes.

The construction of a cottage or country house is a complex and time-consuming process. And to ensure that the future structure has stood for several decades, it is necessary to comply with all norms and standards when it is erected. Therefore, each stage of construction requires accurate calculations and the quality performance of the necessary work.

One of the most important indicators in the construction and finishing of the structure is the thermal conductivity of building materials. SNIP (building codes) provides a full range of information on this issue. It is necessary to know that the future building is comfortable for living both in summer and in winter.

Perfect warm home

The comfort and economy of living in it depend on the structural features of the structure and the materials used in its construction. Comfort consists in creating an optimal microclimate inside regardless of external weather conditions and ambient temperature. If the materials are selected correctly, and the boiler equipment and ventilation are installed according to the norms, then in such a house there will be a comfortable cool temperature in summer and warm in winter. In addition, if all materials used in construction have good thermal insulation properties, then energy costs for heating the premises will be minimal.

The concept of heat conduction

Thermal conductivity is the transfer of heat energy between directly contacting bodies or media. In simple words, thermal conductivity is the ability of a material to conduct a temperature. That is, getting into some environment with a different temperature, the material begins to take the temperature of this environment.

This process is of great importance in construction. So, in the house with the help of heating equipment the optimum temperature (20-25 ° C) is maintained. If the temperature in the street is lower, then when the heating is turned off, all the heat from the house after a while will go out and the temperature will drop. In the summer, the opposite situation occurs. To make the temperature in the house lower than the street, you have to use air conditioning.

Coefficient of thermal conductivity

The loss of heat in the house is inevitable. It occurs constantly when the temperature outside is less than in the room. But its intensity is a variable. It depends on many factors, the main among which are:

• Area of ​​surfaces involved in heat exchange (roof, walls, floors, floor).
• The index of thermal conductivity of building materials and individual building elements (windows, doors).
• The difference between the temperatures on the street and inside the house.
• And others.

To quantify the thermal conductivity of building materials use a special coefficient. Using this indicator, you can easily calculate the necessary insulation for all parts of the house (walls, roof, floors, floors). The higher the thermal conductivity of building materials, the greater the loss of heat. Thus, for the construction of a warm house it is better to use materials with a lower value of this value.

The coefficient of thermal conductivity of building materials, as well as of any other substances (liquid, solid or gaseous), is denoted by the Greek letter λ. The unit of its measurement is W / (m * ° C). In this case, the calculation is carried out on one square meter of a wall one meter thick. The temperature difference here is taken to be 1 °. Practically in any construction manual there is a table of thermal conductivity of building materials, in which you can see the value of this coefficient for various blocks, bricks, concrete mixtures, wood species and other materials.

Determination of heat loss

There is always a loss of heat in any building, but depending on the material, they can change their meaning. On average, heat loss occurs through:

• The roof (from 15% to 25%).
• Walls (from 15% to 35%).
• Windows (from 5% to 15%).
• The door (from 5% to 20%).
• Sex (from 10% to 20%).

To determine the heat loss, a special thermal imager is used, which determines the most problematic places. They are highlighted in red. Less heat loss occurs in the yellow zones, then - in green. Zones with the least loss of heat are highlighted in blue. A definition of the thermal conductivity of building materials should be carried out in special laboratories, as evidenced by the quality certificate attached to the products.

Example of heat loss calculation

If we take, for example, a wall made of a material with a coefficient of thermal conductivity of 1, then with a temperature difference on both sides of this wall of 1 °, the heat loss will be 1 W. If wall thickness   take not 1 meter, but 10 cm, then the losses will amount to 10 watts. In the event that the temperature difference is 10 °, then the heat loss will also be 10 W.

Let us now consider, with a concrete example, the calculation of the heat loss of an entire building. The height of it will be 6 meters (8 with a ridge), width - 10 meters, and length - 15 meters. For ease of calculations, we take 10 windows with an area of ​​1 m 2. The temperature inside the room will be considered equal to 25 ° C, and on the street -15 ° C. We calculate the area of ​​all surfaces through which heat loss occurs:

• Windows - 10 m 2.
• The floor is 150 m 2.
• The walls are 300 m 2.
• The roof (with ramps along the long side) is 160 m 2.

The formula for the thermal conductivity of building materials makes it possible to calculate the coefficients for all parts of the building. But it is easier to use already prepared data from the directory. There is a table of thermal conductivity of building materials. We consider each element separately and determine its thermal resistance. It is calculated by the formula R = d / λ, where d is the thickness of the material, and λ is the coefficient of its thermal conductivity.

Floor - 10 cm of concrete (R = 0.058 (m 2 * ° C) / W) and 10 cm of mineral wool (R = 2.8 (m 2 * ° C) / W). Now add these two indicators. Thus, the thermal resistance of the floor is 2.858 (m 2 * ° C) / W.

Similarly, the walls, windows and roof are considered. Material - cellular concrete (aerated concrete), thickness 30 cm. In this case, R = 3.75 (m 2 * ° C) / W. The thermal resistance of the formation window is 0.4 (m 2 * ° C) / W.

The following formula allows us to determine the loss of thermal energy.

Q = S * T / R, where S is the surface area, T is the temperature difference between the outside and inside (40 ° C). Calculate the heat loss for each element:

• For the roof: Q = 160 * 40 / 2.8 = 2.3 kW.
• For walls: Q = 300 * 40 / 3.75 = 3.2 kW.
• For windows: Q = 10 * 40 / 0,4 = 1 kW.
• For the floor: Q = 150 * 40 / 2,858 = 2,1 kW.

Further, all these indicators are summarized. Thus, for this cottage, the heat loss is 8.6 kW. And to maintain the optimum temperature, boiler equipment with a capacity of at least 10 kW will be required.

Materials for external walls

To date, there are many wall building materials. But the most popular in private housing construction is still using building blocks, bricks and wood. The main differences are the density and thermal conductivity of building materials. Comparison makes it possible to choose the golden mean in the density / thermal conductivity relation. The higher the density of the material, the higher its bearing capacity, and consequently, the strength of the structure as a whole. But at the same time, its thermal resistance is lower, and as a result, energy costs are higher. On the other hand, the higher the thermal resistance, the lower the density of the material. Less dense, as a rule, implies the presence of a porous structure.

To weigh the pros and cons, you need to know the density of the material and its thermal conductivity. The following table of the thermal conductivity of building materials for walls gives the value of this coefficient and its density.

Wall insulation for walls

If there is insufficient thermal resistance of external walls, different heaters can be used. Since the values ​​of the thermal conductivity of building materials for insulation can be very low, most often a thickness of 5-10 cm will be enough to create a comfortable temperature and microclimate in the premises. Widely used today are materials such as mineral wool, expanded polystyrene, expanded polystyrene, foam polyurethane and foam glass.

The following table of the thermal conductivity of building materials used for the insulation of external walls gives the value of the coefficient λ.

Features of the use of wall heaters

The use of insulation for exterior walls has some limitations. This is primarily associated with a parameter such as vapor permeability. If the wall is made of a porous material, such as aerated concrete, foam concrete or expanded clay, then it is better to apply mineral wool, since this parameter is almost the same for them. The use of expanded polystyrene, polyurethane foam or foam glass is possible only if there is a special ventilation gap between the wall and the heater. For a tree, this is also critical. But for brick walls, this parameter is not so critical.

Warm roofing

Insulation of the roof allows you to avoid unnecessary overruns when heating the house. For this, all types of insulation, both sheet format and sprayed (foam polyurethane) can be used. In this case, do not forget about the vapor barrier and waterproofing. This is very important, because the wet insulation (mineral wool) loses its properties in terms of thermal resistance. If the roof is not insulated, then it is necessary to thoroughly insulate the floor between the attic and the last floor.

Floor

Warming of the floor is a very important stage. It is also necessary to apply vapor barrier and waterproofing. As a heater used more dense material. It, accordingly, has a higher coefficient of thermal conductivity than roofing. An additional measure for warming the floor can serve as a basement. The presence of air layer allows to increase the thermal protection of the house. And the equipment of the system of a warm floor (water or electric) gives an additional source of heat.

Conclusion

When building and finishing the facade, it is necessary to be guided by accurate calculations for thermal losses and take into account the parameters of the materials used (thermal conductivity, vapor permeability and density).