How to determine the dew point. Dew point in the wall - calculation and determination. The term "dew point" in construction

When building a residential building, bathhouse or other building, any developer must take into account such important parameter, like the dew point - an indicator of the concentration of water vapor in the air. An increase in humidity entails an increase in the point, which can be the main reason for the formation of condensation and the development of mold. For competent organization thermal insulation protection buildings, it is important to understand how to correctly calculate given parameter and where it might be located.

What is dew point?

This is a parameter that determines the condensation of moisture from surrounding air masses. In this case, the temperature and humidity conditions in the premises may exceed the heating temperature of the walls, which leads to inevitable condensation of moisture on various surfaces.

The dew point is influenced by:

• Humidity level and temperature regime inside the building.
• Heating temperature of walls and ceilings.

If the interior is warm and humid enough, then excess moisture will condense on colder substrates – window frames, walls and ceilings.

During the construction of a house, windows, doors and walls work as special enclosing structures that protect the premises inside any building from adverse effects external factors. Therefore, the temperature of such structures will always differ from the indoor air temperature, which can be the main reason for the appearance of condensation.

The dew point value can vary according to the thickness of the ceiling, taking into account temperature fluctuations outside and inside the building. When maintaining a constant microclimate in the building and a sharp change in temperature outside, a shift of the problem area to the inside of the ceiling is noted.

When the thickness of the ceiling is small and it is sufficiently cooled, condensation appears on the internal surfaces. This can lead to deformation of the cladding and the formation of mold.

Factors influencing dew point

Its location is influenced by the following factors:

• Climatic conditions of the region.
• Temporary or permanent mode of operation of premises.
• Materials for the construction and insulation of walls.
• Floor thickness, thermal insulation layer.
• Air temperature and humidity level indoors and outdoors.
• What is located behind the insulated ceiling (room, street).
• Functionality of the ventilation system.
• Efficiency of the heating system.
• Thermal insulation of other structural elements of the building.

An important role is played by ventilation and heating systems, which are designed to maintain optimal microclimate indoors. Thus, an increase in air humidity inevitably leads to an increase in the dew point value.

Being in the wall

For more understanding this process Let's consider several options for how the dew point in the wall can be located.

1. The building is not insulated. If brick, block and wooden walls do not have additional thermal insulation, the desired location will depend on climatic conditions. In the absence of sudden changes in temperature, it will be located near the outer surface of the ceiling, while the interior will be comfortable and warm. With significant cooling, the problem area will be shifted to inner surface walls, which will lead to constant wetting of surfaces and the appearance of condensation.
2. The building is insulated from the outside. If the house has facade insulation, then the location of the condensation section will depend on the thickness of the thermal insulation. If the external insulation technology is followed, it will be located inside the insulating layer. Otherwise, reduce heat losses indoors will be quite difficult.
3. The building is insulated inside. With internal insulation, the area will be located between the insulating material and the middle of the floor. It's not the best suitable option, since a significant decrease in the temperature outside will lead to the formation of condensation at the junction of the insulator and the wall. This can cause destruction of the insulation right up to the surface of the ceiling. Internal insulation is possible only if there is an effective heating system, which will ensure the maintenance optimal temperature heating the air in all rooms.

Important! To stabilize the dew point in the wall, in most cases it is recommended to carry out external insulation of buildings.

Calculation methods

To avoid possible troubles caused by high humidity in the premises, it is necessary to correctly calculate the temperature value in the ceilings. It is important to understand that this parameter is individual, so calculations should be carried out for each individual building.

• According to the table.
• According to the formula.

Table calculations

Calculation of the dew point for thermal insulation of a building is carried out on the basis of a special table prepared based on the results of data from research and design organizations.

It indicates the values ​​of temperature conditions and relative humidity in rooms at which condensation may form on surfaces.

Calculations using the formula

To determine the dew point value, a simple formula is used:

Tp – point value,

a, b – constant values,

ƛ (T, Rh) – coefficient that can be calculated using the formula:

T – internal temperature,

Rh – internal humidity level,

Ln – natural logarithm.

Let's try to determine the value for the following conditions: air temperature – 23 °C, relative humidity level – 60%.

First you need to find the coefficient:

ƛ (T, Rh) = (17.27×23) / (237.7+23) + Ln (60/100) = 1.52362 + (-0.51083) = 1.01279.

Parameter Definition:

Tp = (237.7×1.01279) / (17.27×1.01279) = 240.74 / 17.490 = 13.76 °C.

In this case, cooling the wall surface to 13.7 degrees will lead to the formation of condensation.

Necessary measurements for calculations

To obtain the point value, it is necessary to carry out basic measurements of temperature and humidity conditions indoors. To do this you will need the following equipment:

• Hygrometer.
• Regular and non-contact thermometer.

Measurements are carried out according to the following scheme:

1. In the room where it is necessary to determine the problem area, a distance of 55 cm is measured from the floor. At this height, the air temperature is measured.
2. At the same level, humidity is measured.
3. In the table below, the obtained values ​​are selected to determine the point. For convenience, you can create a simple graph of values ​​for all rooms.
4. Next, the feasibility of conducting internal repair work. To do this, using a non-contact thermometer, the temperature of various surfaces, for example, walls, partitions, window frames, is measured.
5. Finally, a comparison of the results obtained is carried out. If the surface temperature exceeds the air temperature by more than 5 degrees, this indicates increased humidity and the presence of a problem area. In this case, thermal insulation work requires a competent selection of insulation and determination of the appropriate thickness of the protective layer.

How to change the location of a point

If errors in calculations were made during the construction of a new house, this can lead to the constant formation of mold on surfaces with low temperatures and further destruction of the entire structure.

The problem in a house that has been in use for a long time can be solved by changing the main influencing factors. The following activities are provided for this:

1. Arrangement reliable system ventilation. If a finished building (guest house, bathhouse or cottage) is used temporarily, for example, in the summer, an increase in humidity levels in all rooms may be observed. Most correct solution– organization of a ventilation system for good air exchange at any time of the year.
2. Additional heating. If floor surfaces are constantly condensing, it means that heating the premises is not enough to reduce humidity levels. The best decision– additional use of mobile phones heating devices or household dehumidifiers.
3. Thermal insulation of the building. You can move the point towards the street using façade insulation of surfaces. Why is it beneficial to insulate walls from the outside? In this case, the condensation point will be located between the insulator and the wall, so even with a significant change in climatic conditions, wetting of the surfaces can be prevented.

When determining the location of a point in the wall, it is necessary to take into account many factors: climatic conditions, wind strength, impact angle sun rays, temperature, humidity conditions indoors, the thickness of the floors and the materials from which they are made.

The minimum level of humidity is typical for any type of material; the main thing is to prevent its significant increase. In addition, any homeowner can independently determine the temperature regime of surface condensation. And if the thermal insulation technology is followed, we can safely talk about reliable protection and durability of walls.

In this article I will tell you what dew point is, how it is determined and how important it is to understand the influence of this factor during the construction and insulation of the building envelope.

The meaning of dew point

What it is?

Dew point is the ratio of air temperature and humidity at which water vapor in the air begins to condense into liquid water. This may look like fog, water droplets on various surfaces, glass fogging, etc.

"Crying glass" is a sign that its temperature has reached or become lower than the dew point.

To be precise from a physics point of view, you will have to take into account a number of other factors, such as pressure, wind speed, etc. But we will assume that the change in temperature and humidity occurs isobarically, that is, with constant pressure.

The humidity in the room is also approximately the same. In GOST 30494-96 it is prescribed as 30 - 60%, but according to doctors it should be higher. The same Komarovsky O.E. advises no less than 60%, and for patients with ARVI - no less than 70%. The maximum is 80%, so we will take middle option air humidity – 70%.

In our case, the dew point (DP) is the temperature at which water vapor in air humidified to 70% begins to condense and fall out in the form of dew (fog, drops, etc.).

The influence of dew point on building structures

Let me remind you that we assumed the humidity was constant and equal to 70%. We neglect the influence of pressure difference and other factors. The main parameter that has an impact is temperature.

Let me give you a simple example: the temperature in the room is +20 °C, the relative humidity is 70%. I will not give a formula for calculating the dew point temperature; it is easier to use a table where the calculations have already been performed:

In the table we find that the dew point temperature is 14.4 °C. Now take a bottle of water and cool it in the refrigerator to a temperature below 14.4 °C. Moreover, the colder the water, the faster and more noticeable the effect will be.

We bring a chilled bottle of water into the room and after a while we see that its walls “fog up”, that is, they become covered with tiny drops of water. This is the phenomenon of water vapor on a surface whose temperature is equal to or below the dew point.

That is, we clearly saw that upon reaching certain temperature and further cooling, the water vapor in the air turns into liquid state:

• if the air reaches the temperature TP, then fog falls or steam comes out of the mouth;
• if these are objects, then water settles on their surface.

Now let’s imagine a situation where the wall has absorbed a certain amount of steam (the so-called breathing of the walls), and at that moment the air temperature outside has dropped sharply. The closer to outer surface walls, the lower the temperature of the material. In a certain place this temperature reaches 14.4 °C and further, as you approach the street, it becomes lower.

The steam that the wall has absorbed along with the air will turn into water, since the TR has been passed since 14.4 ° C. As a result, the wall will get wet. If the temperature outside drops further, at some point the water will freeze.

As you know, the service life of building envelopes is measured by the number of freeze / thaw cycles. Therefore, every time a liquid forms inside the wall and then freezes, the structure loses its durability.

For water to freeze, it is necessary either low temperature on the street, or absence. These are very rare conditions, in addition, today there are a lot of heaters for walls. But here, too, not everything is simple.

Let's look at the process step by step:

1. The temperature in the room is +20 °С, outside +10 °С, the walls are dry and there are no problems.
2. After some time, it gets cold outside to -20 °C, but the heating is on in the apartment, moreover, the walls are insulated with polystyrene foam, for example.
3. The following situation arises: the temperature on the inner surface of the wall is about +20 °C, and on the outer surface of the insulation – about -20 °C.

1. As we remember, TP corresponds to a temperature of 14.4 °C, and this value is between +20 and – 20 degrees. That is, inside the wall.
2. If this point is located close to or on the inner surface, the wall will get wet from the inside, the finish will deteriorate, and fungus will grow under the wallpaper. But if the wall is insulated with foam plastic, such a position of the dew point is hardly possible.

1. If the dew point is located close to the outer surface of the wall or right on it, this will not clearly affect the inner surface of the structure, and everything will appear to be in order.
2. However, we must not forget that polystyrene foam is a vapor-opaque substance, and moisture formed in the wall will not be able to escape outside. It will accumulate until it saturates the entire wall.
3. If it turns out that the dew point is in the foam, then there will be no problems, since there is simply no steam there, and if there is, then its amount can be neglected.

1. If the wall is not insulated, then the position of the TP near its outer surface is not dangerous, since the water will evaporate into the street. However, if the liquid in the wall freezes, the material will still deteriorate.

You can shift the dew point by changing the thickness of the insulation. The thicker it is, the closer to the outer surface of the wall is the TR. The goal of calculating the insulation parameters is to achieve a shift in the dew point beyond the outer surface of the wall so that it always remains dry.

But how to choose the thickness of the thermal insulation layer to move the dew point beyond the wall? To do this, it is necessary to calculate the thermal resistance of the wall for a given region.

If this figure turns out to be insufficient, then we will have to increase it using insulation, the thickness of which will have to be calculated.

According to tradition, we take the value of heat transfer resistance from the table:

Let's say that we bought an apartment in St. Petersburg with reinforced concrete walls 500 mm thick. For St. Petersburg, minimum heat transfer resistance external wall should be R = 4.6 m²*°C/W.

To determine the real value of R for our wall, it is necessary to divide the resistance index by the thermal conductivity of reinforced concrete. It is also easy to determine:

So, we know the thickness of the wall B = 0.5 m, the thermal conductivity of reinforced concrete t = 2.04 W/m*°C and the value of the required heat transfer resistance of the wall for our region (St. Petersburg) R = 4.6 m²*°C/W.

To find out the R value for a specific wall, you need to divide its thickness by the thermal conductivity coefficient:

R1 = 0.5/2.04 = 0.25 m²*°C/W.

As you can see, our wall is significantly inferior to the required value of heat transfer resistance. This means it needs to be insulated. Let's determine what resistance the insulation should have (let's call it R2):

R2 = R (St. Petersburg) – R1 = 4.6 – 0.25 = 4.35 m²*°C/W.

Let's assume that to insulate the wall we will use polystyrene foam, the thermal conductivity of which is 0.05 W/m*°C. Knowing all these parameters, we can calculate the thickness of the foam layer P:

P = t*R2 = 0.05*4.35 = 0.22 m.

Taking into account the layer of glue and plaster, this figure can be rounded to 0.2 m or 20 cm. This is the typical thickness of PSB-S-25 foam for wall insulation in regions with a similar climate.

After such a calculation, the dew point will shift into the thickness of the foam, and your walls will always be dry. This means they will not only be warm, but will also last much longer.

You will save on heating due to thermal insulation and extend the life of your home - that’s how important the dew point is in construction.

Inside or outside

It would seem, why not insulate the apartment indoors? Especially if you live on the 10th floor? The idea is tempting, but absolutely absurd.

Of course, working at home with your own hands without any climbing or ladders is much more pleasant and convenient, but there are a number of significant obstacles:

1. A layer of insulation will cut off the walls from the heating system, and in winter they will freeze. This will cause them to wear out quickly.
2. The dew point position will be inside the wall at best, but most likely it will be located immediately under the insulation layer.
3. The volume of the living space will be significantly reduced due to the thickness of the thermal insulation layer.
4. The walls will stop absorbing moisture, the humidity in the room will increase, which will feel uncomfortable. In some cases, a strong increase in humidity leads to asthma.
5. Wet walls will become an excellent habitat for mold and bacteria..

If my warnings do not convince you, then read the provisions dictated by the SNiP and GOST instructions.

Internal insulation can be justified only in cases where external installation of thermal insulation is impossible for some reason. The slightest mistake in calculations or performance of work can lead to disastrous consequences.

Conclusion

I talked about all the nuances of such a thing as dew point. Now you know how important it is to understand the impact of this phenomenon on building construction and prevent the dew point in the wall from ruining your interior and even your exterior walls.

Be sure to watch the video in this article and ask questions in the comments.

When describing the work of installing thermal insulation of buildings, unknown phrases are encountered. For example, you should know what “dew point” means. This is easy to explain using an everyday example.

The higher the relative humidity, the higher the dew point and the closer to the actual air temperature

Air is a mixture of nitrogen, oxygen, other gases and steam. The temperature at which steam condenses occurs has acquired the concept of dew point. This phenomenon occurs when a kettle boils and the vapor forms water droplets on cold surfaces.

Formula for calculation

This formula can be used to calculate relative humidity from a known dew point

Here Tr means the temperature of the point itself, b and a show equal (constant) values, ln is the natural logarithm, T is the indoor temperature, Rh is the relative humidity value.

As can be seen from the formula, the value directly depends on the values ​​of two parameters:

• humidity indicator;
• actual temperature readings.

At high relative humidity, the parameter becomes higher and closer to the actual temperature level. To count this variable value, there is a table with a small step of parameters. You can find it required value by measuring relative humidity and actual temperature.

​From the table we calculate that at a temperature of, for example, 19 degrees and a humidity of 50%, the condensation parameter will be 8.3 degrees.

From this video it becomes clear how thick the insulation should be for the most comfortable conditions:

The term "dew point" in construction

The constantly growing and developing construction products market represents wide choose materials for thermal insulation. The choice of thermal insulation for industrial and residential premises must be approached properly and during construction, pay attention to the indicator in question.

Experts consider the boundary of transition from low temperatures outside the walls to higher temperatures inside heated structures with the possible formation of condensation to be the dew point. Drops of water will appear on any surface in the room whose temperature is close to the dew point parameter or reaches a value lower. The simplest example: in the middle of some rooms in cold weather window glass condensation drains.

The main factors influencing the determination of the value are:

• climatic factors (temperature and air humidity outside);
• temperature values ​​inside;
• indoor humidity indicator;
• wall thickness;
• vapor permeability of thermal insulation used in construction;
• availability of heating and ventilation systems;
• purpose of structures.

Only if the indicator is measured correctly can the building be used comfortably in the future and will reduce maintenance costs in the future.

Precise definition

Water vapor most often condenses on the walls themselves or inside their structure if they are not insulated or built properly. Without insulation, the value will be close to the temperature of the inside of the wall, and in some cases, the wall in the middle of the house. When the temperature inside the enclosing structures is below the value, then during a cold snap negative temperature Condensation will form outside.

There are several places where the indicator may be located on non-insulated structures:

• inside the structure, close to its outer part, the wall will remain dry;
• inside the wall, but close to the inside, the wall becomes wet with temperature changes;
• the side of the wall that is located in the building will constantly be covered with condensation.

Experts do not recommend insulating rooms from the inside, explaining that when using this method of thermal insulation, the parameter will be located under the heat-insulating layer in the middle of the room . As a result, a large accumulation of moisture will occur.

• condensation can accumulate in the center of the wall and, during cold weather, move towards the placement of heat-insulating components;
• the place where moisture accumulates can be the boundary of the enclosing structure and the insulating layer, which becomes damp and forms mold in the middle of the rooms;
• in the middle of the heat-insulating layer itself (it will gradually become saturated with moisture and begin to mold and rot from the inside).

Polystyrene foam, mineral wool or other type of insulation must be placed with outside building, which will allow you to place the value in the insulating layer (with this arrangement, the walls inside will remain dry). For a clearer understanding of the parameter, there are graphs for its placement on the walls of houses with insulation, as well as on buildings that do not have an insulating layer. To make this calculation yourself, you can determine the dew point in the wall with a calculator.

Wrong definition of value

The result of errors made during the calculation of parameters will be a constant accumulation of condensate, high humidity, the development of fungal plaque and mold. Industrial, administrative or residential premises will not last long: negative processes will accelerate destruction. Additional costs will be required for routine maintenance and major repairs.

Insulating your home allows you not only to live in comfort, but also to pay less for heating. The insulation process begins with the choice of thermal insulation method and selection of thermal insulation materials. At first glance, everything seems simple: add a layer of good thermal insulation material to the thickness of the wall and enjoy the warmth and comfort!

In reality, everything turns out to be much more complicated. There are many videos on the Internet with stories about mold on the walls and the destruction of buildings, the cause of which was simply improper insulation structure, or more precisely, the position of the dew point inside the house or in the wall mass, which led to the accumulation of moisture on the surface of the walls.

Correct determination of the dew point in the wall is the main condition for carrying out high-quality, reliable and effective insulation Houses.

In physics, the dew point is the temperature of a gas at which the water vapor present in it, at constant pressure, changes from a gaseous state to a liquid state. At the same time, condensation forms in the air, or, as is often said, dew falls.

The dew point is inextricably linked to the concentration of water vapor in the air: the higher it is, the higher the dew point temperature. A simple example, in a bathhouse, in a steam room, condensation forms even at a temperature close to 100 C. To form drops of water in a steam room, it is enough to come into contact with any surface whose heating is at least slightly lower than its temperature.

The level of concentration of water vapor in the air is called humidity. A hygrometer is used to determine humidity. In a living room at an air temperature of 20-25 C, a humidity of 40-60% is considered normal.

You can determine the dew point for a living space using thermal tables.

For an average living space, its value is in the range from 6 to 12 C. This means that condensation will necessarily form on any surface that has a temperature equal to or below the dew point temperature (12 C and below) placed in a living room. This is exactly the phenomenon that can be observed on the surface of bad windows during the cold season.

What do the walls have to do with it?

You ask, because their inner surface in a heated apartment or house is always warm and has the ambient temperature, and in places where radiators are installed, it exceeds it.

Indeed, condensation does not form on the inner surface of the walls... until you decide to insulate them from the inside, using any thermal insulation material you like. It doesn't matter if you take it vapor permeable insulation based stone wool or give preference to polystyrene - the effect will be approximately the same. Over time, moisture forms on the inner surface of the walls under the insulation layer, the accumulation of which can lead to mold. This is due to the dew point on the inner surface of the walls.

Where is it, the dew point?

The temperature of the inner surface of the wall of the house is equal to the temperature of the room, and the temperature of the outer surface of the wall of the house is equal to the temperature environment. During the cold season, there may be a temperature difference between inside and outside of 30 degrees or more.

Heat loss through the wall surface can be represented graphically by connecting the temperature mark inside and outside the house with a straight line. The temperature drop in the thickness of the wall is gradual and the more intense, the smaller the thickness of the wall or the higher the thermal conductivity of the materials from which it is made, but in any case, with a homogeneous composition of the wall (for example, only made of brick), the dew point temperature (12 C and below) will be inside the wall.

It is here, inside the wall, that condensation forms, which leads to freezing of the walls and their destruction during repeated cycles of freezing and thawing. For this reason, it is recommended to heat the house constantly, maintaining the temperature of the walls at the same level, trying to eliminate periods of thawing of the building and new freezing.

It should be noted that no matter what material the house is built from, its walls are always vapor-permeable to one degree or another. There is always some amount of moisture present inside the wall.

If the walls are insulated from the inside

When the thermal insulation material is located on the inner surface of the walls (Fig. 1), the main temperature drop will occur through the thickness of the thermal insulation. As a result, the temperature of its surface inside the house will be equal to the temperature of the room, and the temperature of the external surface, depending on the thickness of the insulating material and its quality, will be below the dew point temperature. In this case, the temperature of the wall behind the thermal insulation layer will be even lower by 1-3 C, which will invariably lead to condensation.

It turns out that the water vapor in the house, trying to escape outside, passes through the heat-insulating material, cools down and condenses on interior walls, without getting into their thickness, even if a building material with good vapor permeability is used for the walls.

There can be only one conclusion: you cannot insulate a house from the inside!

How to bring the dew point out?

When thermal insulation material is located outside the walls, the ambient temperature will be not the wall, but outer layer thermal insulation. The temperature drop graph in this case will be flatter, and the dew point temperature on it, depending on the difference in temperatures outside and inside the house, will be located outside the wall in the thickness of the thermal insulation material or in the wall, but in close proximity to its outer surface.

It turns out that the thicker the layer of thermal insulation, the more likely it is that the dew point will be located outside the wall, which means that the walls of the house that are well insulated from the outside will always be dry, which will increase the service life of the building.

How to calculate dew point?

To calculate the dew point in a wall, the methodology for designing thermal protection of buildings is used, described in detail in the Code of Rules for Design and Construction SP 23-101-2004. An approximate primitive calculation is unlikely to help with this.

You can get reliable results by using the services of the appropriate online calculators, which are easy to find on the Internet.

Which thermal insulation material should you prefer?

The concept of dew point in a wall allows you to better understand and imagine the physical processes associated with heat loss through the plane of the wall and correctly select the thermal insulation material, while determining the methods of its installation.

As a rule, you have to choose between mineral wool and expanded polystyrene.

Thermal insulation materials based on mineral wool They are characterized by vapor permeability and, when the dew point is in their array, do not interfere with the movement of steam and its release out into the atmosphere. Of course, we are talking only about part of the water vapor. The remaining part will turn into water and flow down the insulation layer. By the way, everyone thermal insulation materials made of basalt and fiberglass, they are resistant to moisture, not susceptible to mold and can withstand repeated cycles of thawing and freezing. So the position of the dew point in the thermal insulation layer will not harm it.

Expanded polystyrene is not vapor permeable. Therefore, moisture will accumulate on its inner surface. To remove it between the wall and the thermal insulation layer, you need to leave a groove, making guides in them. Only in this case can we talk about the safety of the walls and high quality their insulation.

In order to understand what consequences the lack of a ventilated gap in walls made of two or more layers will lead to different materials, and whether gaps in walls are always needed, it is necessary to recall the physical processes occurring in the outer wall in the event of a temperature difference on its inner and outer surfaces.

As you know, the air always contains water vapor. The partial pressure of vapor depends on the air temperature. As temperature increases, the partial pressure of water vapor increases.

During the cold season, the partial vapor pressure indoors is significantly higher than outside. Under the influence of pressure differences, water vapor tends to enter an area of ​​lower pressure from inside the house, i.e. on the side of the material layer with a lower temperature - on the outer surface of the wall.

It is also known that when air is cooled, the water vapor contained in it reaches extreme saturation, after which it condenses into dew.

Dew point- this is the temperature to which the air must cool so that the vapor it contains reaches a state of saturation and begins to condense into dew.

The diagram below, Fig. 1, shows the maximum possible content of water vapor in the air depending on temperature.

The ratio of the mass fraction of water vapor in air to the maximum possible fraction at a given temperature is called relative humidity, measured as a percentage.

For example, if the air temperature is 20 °C, and the humidity is 50%, which means that the air contains 50% of the maximum amount of water that can be found there.

As is known Construction Materials have different abilities pass water vapor contained in the air, under the influence of their difference partial pressures. This property of materials is called vapor permeation resistance, measured in m2*hour*Pa/mg.

To briefly summarize the above, in winter period air masses, which include water vapor, will pass through the vapor-permeable structure of the external wall from the inside to the outside.

The temperature of the air mass will decrease as it approaches the outer surface of the wall.

In a dry wall there is a vapor barrier and a ventilated gap

The dew point in a properly designed wall without insulation will be in the thickness of the wall, closer to the outer surface, where steam will condense and moisten the wall.

In winter, as a result of the transformation of steam into water at the condensation boundary, the outer surface of the wall will accumulate moisture.

IN warm time this year accumulated moisture must be able to evaporate.

It is necessary to ensure a shift in the balance between the amount of vapor entering the wall from inside the room and the evaporation of accumulated moisture from the wall towards evaporation.

The balance of moisture accumulation in the wall can be shifted towards moisture removal in two ways:

1. Reduce the vapor permeability of the inner layers of the wall, thereby reducing the amount of vapor in the wall.
2. And (or) increase the evaporation capacity of the outer surface at the condensation boundary.

They have the same resistance to vapor permeation throughout the entire thickness, as well as a uniform temperature change across the thickness of the wall. The boundary of water vapor condensation in a properly designed wall without insulation is located in the thickness of the wall, closer to the outer surface. This provides such walls with a positive balance of moisture removal from the wall thickness in all cases, except for rooms with high humidity.

In multi-layer walls materials with different vapor permeability resistance are used with insulation. In addition, the temperature distribution throughout the multilayer wall is not uniform. At the boundary of layers in the thickness of the wall we have sudden changes temperature.

To ensure the required balance of moisture movement in a multilayer wall, it is necessary that the resistance to vapor permeation of the material in the wall decreases in the direction from the inner surface to the outer.

Otherwise, if the outer layer has greater resistance to vapor permeation, the balance of moisture movement will shift towards the accumulation of moisture in the wall.

For example.

The resistance to vapor permeation of aerated concrete is significantly less than that of ceramics. At facade finishing In houses made of aerated concrete and ceramic bricks, a ventilated gap between the layers is required. If there is no gap the blocks will accumulate moisture.

Ventilated gap between face masonry from ceramic bricks And load-bearing wall made of expanded clay concrete blocks is not needed, because The vapor permeability resistance of brick cladding is less than that of a wall made of expanded clay concrete blocks.

If the wall is constructed incorrectly, moisture will gradually accumulate in the insulation.

Already in the second, or maximum third-fifth heating period, it will be possible to feel a significant increase in heating costs. This is naturally due to the fact that the humidity of the heat-insulating layer and the entire structure as a whole has increased, and accordingly the indicator has significantly decreased thermal resistance walls.

Moisture from the insulation will be transferred to adjacent layers of the wall. Fungus and mold can form on the inner surface of external walls.

In addition to moisture accumulation, Another process occurs in the wall insulation - freezing of condensed moisture. It is known that periodic freezing and thawing of a large amount of water in the thickness of the material destroys it.

Wall materials vary in their ability to resist condensation freezing. Therefore, depending on the vapor permeability and frost resistance of the insulation, it is necessary to limit the total amount of condensate accumulating in the insulation during the winter period.

For example, mineral wool insulation has high vapor permeability and very low frost resistance. In structures with mineral wool insulation (walls, attic and basement floors, mansard roofs) To reduce the entry of steam into the structure, a vapor-proof film is always laid from the room side.

Without the film, the wall would have too little resistance to vapor permeation and, as a result, it would be released and frozen in the thickness of the insulation. a large number of water. The insulation in such a wall would turn into dust and crumble after 5-7 years of operation of the building.

The thickness of the thermal insulation must be sufficient to maintain the dew point in the thickness of the insulation, Fig. 2a.

If the insulation thickness is small, the dew point temperature will be on the inner surface of the wall and vapors will condense on the inner surface outer wall, Fig. 2b.

It is clear that the amount of moisture condensed in the insulation will increase with increasing air humidity in the room and with increasing severity of the winter climate at the construction site.

The amount of moisture evaporated from the wall in summer time also depends on climatic factors - temperature and humidity in the construction area.

As you can see, the process of moisture movement in the thickness of the wall depends on many factors. The humidity regime of walls and other fences of the house can be calculated, Fig. 3.

Based on the calculation results, the need to reduce the vapor permeability of the inner layers of the wall or the need for a ventilated gap at the condensation boundary is determined.

Results of calculations of humidity conditions various options insulated walls (brick, cellular concrete, expanded clay concrete, wood) show that in structures with a ventilated gap at the condensation boundary, moisture accumulation in the fences of residential buildings does not occur in all climatic zones Russia.

Multilayer walls without ventilated gap must be applied based on the calculation of moisture accumulation. To make a decision, you should seek advice from local specialists professionally involved in the design and construction of residential buildings. The results of calculating the moisture accumulation of typical wall structures at the construction site have long been known to local builders.

— this is an article about the features of moisture accumulation and insulation of walls made of brick or stone blocks.

Features of moisture accumulation in walls with facade insulation with foam plastic, expanded polystyrene

Insulation materials made from foamed polymers - polystyrene foam, polystyrene foam, polyurethane foam - have very low vapor permeability. A layer of insulation boards made of these materials on the facade serves as a barrier to steam. Steam condensation can only occur at the boundary of the insulation and the wall. A layer of insulation prevents condensation from drying out in the wall.

To prevent moisture accumulation in a wall with polymer insulation it is necessary to exclude steam condensation at the boundary of the wall and insulation. How to do it? To do this, it is necessary to ensure that the temperature at the boundary of the wall and the insulation is always, in any frost, above the dew point temperature.

The above condition for temperature distribution in a wall is usually easily met if the heat transfer resistance of the insulation layer is noticeably greater than that of the insulated wall. For example, “cold” insulation brick wall houses with polystyrene foam thickness 100 mm. V climatic conditions middle zone Russia usually does not lead to moisture accumulation in the wall.

It’s a completely different matter if a wall made of “warm” timber, logs, aerated concrete or porous ceramics is insulated with polystyrene foam. And also, if you choose a very thin polymer insulation for a brick wall. In these cases, the temperature at the boundary of the layers can easily be below the dew point and, to ensure that there is no moisture accumulation, it is better to perform the appropriate calculation.

The figure above shows a graph of temperature distribution in an insulated wall for the case when the heat transfer resistance of the wall is greater than that of the insulation layer. For example, if a wall is made of aerated concrete with a masonry thickness of 400 mm. insulate with foam plastic 50 thick mm., then the temperature at the border with the insulation in winter will be negative. As a result, steam condensation will occur and moisture will accumulate in the wall.

The thickness of the polymer insulation is selected in two stages:

1. They are chosen based on the need to provide the required resistance to heat transfer of the outer wall.
2. Then they check for the absence of steam condensation in the thickness of the wall.

If the check according to clause 2. shows the opposite, then it is necessary to increase the thickness of the insulation. The thicker the polymer insulation, the lower the risk of steam condensation and moisture accumulation in the wall material. But this leads to increased construction costs.

A particularly large difference in the thickness of the insulation, selected according to the above two conditions, occurs when insulating walls with high vapor permeability and low thermal conductivity. The thickness of the insulation to ensure energy saving is relatively small for such walls, and To avoid condensation, the thickness of the slabs must be unreasonably large.

Therefore, for wall insulation made of materials with high vapor permeability and low thermal conductivity more profitable to use mineral wool insulation . This applies primarily to walls made of wood, aerated concrete, gas silicate, large-pore expanded clay concrete.

A vapor barrier from the inside is mandatory for walls made of materials with high vapor permeability for any type of insulation and facade cladding.

For the vapor barrier device, they are made of materials with high resistance to vapor permeability - a primer is applied to the wall deep penetration in several layers, cement plaster, vinyl wallpapers or use a vapor-proof film. Published