Resistance to vapor permeability of materials and thin layers of vapor barrier. Vapor permeability - typical misconceptions Vapor permeability coefficient of the material of the building envelope layer
One of the most important indicators is vapor permeability. It characterizes the ability of cellular stones to retain or pass water vapor. GOST 12852.0-7 contains general requirements for the method for determining the vapor permeability coefficient of gas blocks.
What is vapor permeability
Temperatures are always different inside and outside buildings. Accordingly, the pressure is not the same. As a result, the moist air masses that exist both on the other side of the walls tend to move to a zone of lower pressure.
But since indoors, as a rule, is drier than outside, moisture from the street penetrates into the micro-crevices of building materials. Thus, wall structures are filled with water, which can not only worsen the microclimate in the premises, but also adversely affect the enclosing walls - they will begin to collapse over time.
The occurrence and accumulation of moisture in any walls is an extremely dangerous factor for health. So, as a result of such a process, not only does the thermal protection of the structure decrease, but fungi, mold and other biological microorganisms also appear.
Russian standards regulate that the vapor permeability index is determined by the ability of the material to resist the penetration of water vapor into it. The vapor permeability coefficient is calculated in mg / (m.h.Pa) and shows how much water will pass within 1 hour through 1m2 of a surface 1 m thick, with a pressure difference from one and the other part of the wall - 1 Pa.
Vapor permeability of aerated concrete
Cellular concretes consist of closed air pockets (up to 85% of the total volume). This significantly reduces the material's ability to absorb water molecules. Even penetrating inside, water vapor quickly evaporates, which has a positive effect on vapor permeability.
Thus, it can be stated that this indicator directly depends on aerated concrete density - the lower the density, the higher the vapor permeability, and vice versa. Accordingly, the higher the brand of porous concrete, the lower its density, and hence this figure is higher.
Therefore, to reduce vapor permeability in the production of cellular artificial stones:
Such preventive measures lead to the fact that the performance of aerated concrete of various grades has different vapor permeability values, as shown in the table below:
Vapor permeability and interior finish
On the other hand, the moisture in the room must also be removed. For this for use special materials that absorb water vapor inside buildings: plaster, paper wallpaper, wood, etc.
This does not mean that it is not necessary to ennoble the walls with tiles burned in ovens, plastic or vinyl wallpaper. And reliable sealing of window and door openings is a prerequisite for high-quality construction.
When performing interior finishing work, it should be remembered that the vapor permeability of each finishing layer (putty, plaster, paint, wallpaper, etc.) must be higher than the same indicator of cellular wall material.
The most powerful barrier to the penetration of moisture into the inside of the building is the application of a primer layer on the inside of the main walls.
But do not forget that in any case, in residential and industrial buildings there must be an effective ventilation system. Only in this case can we talk about normal humidity in the room.
Aerated concrete is an excellent building material. In addition to the fact that buildings built from it perfectly accumulate and retain heat, they are not too wet or dry in them. And all thanks to good vapor permeability, which every developer should know about.
To create a favorable microclimate in the room, it is necessary to take into account the properties of building materials. Today we will analyze one property - vapor permeability of materials.
Vapor permeability is the ability of a material to pass vapors contained in the air. Water vapor penetrates the material due to pressure.
They will help to understand the issue of the table, which cover almost all the materials used for construction. After studying this material, you will know how to build a warm and reliable home.
Equipment
When it comes to Prof. construction, then it uses specially equipped equipment to determine vapor permeability. Thus, the table that is in this article appeared.
Today the following equipment is used:
- Scales with a minimum error - an analytical type model.
- Vessels or bowls for experiments.
- Instruments with a high level of accuracy for determining the thickness of layers of building materials.
Dealing with property
There is an opinion that "breathing walls" are useful for the house and its inhabitants. But all builders think about this concept. “Breathable” is the material that, in addition to air, also allows steam to pass through - this is the water permeability of building materials. Foam concrete, expanded clay wood have a high rate of vapor permeability. Walls made of brick or concrete also have this property, but the indicator is much less than that of expanded clay or wood materials. 
Steam is released when taking a hot shower or cooking. Because of this, increased humidity is created in the house - an extractor hood can correct the situation. You can find out that the vapors do not go anywhere by the condensate on the pipes, and sometimes on the windows. Some builders believe that if the house is built of brick or concrete, then the house is "hard" to breathe.
In fact, the situation is better - in a modern home, about 95% of the steam leaves through the window and the hood. And if the walls are made of breathable building materials, then 5% of the steam escapes through them. So residents of houses made of concrete or brick do not particularly suffer from this parameter. Also, the walls, regardless of the material, will not let moisture through due to vinyl wallpaper. The "breathing" walls also have a significant drawback - in windy weather, heat leaves the dwelling.
The table will help you compare materials and find out their vapor permeability index:
The higher the vapor permeability index, the more moisture the wall can contain, which means that the material has low frost resistance. If you are going to build walls from foam concrete or aerated concrete, then you should know that manufacturers are often cunning in the description where vapor permeability is indicated. The property is indicated for dry material - in this state it really has a high thermal conductivity, but if the gas block gets wet, the indicator will increase by 5 times. But we are interested in another parameter: the liquid tends to expand when it freezes, as a result, the walls collapse.
Vapor permeability in a multi-layer construction
The sequence of layers and the type of insulation - this is what primarily affects the vapor permeability. In the diagram below, you can see that if the insulation material is located on the front side, then the pressure on moisture saturation is lower. 
If the insulation is located on the inside of the house, then condensation will appear between the supporting structure and this building. It negatively affects the entire microclimate in the house, while the destruction of building materials occurs much faster.
Dealing with the ratio
The coefficient in this indicator determines the amount of vapor, measured in grams, that pass through materials with a thickness of 1 meter and a layer of 1 m² within one hour. The ability to pass or retain moisture characterizes the resistance to vapor permeability, which is indicated in the table by the symbol "µ".
In simple words, the coefficient is the resistance of building materials, comparable to the permeability of air. Let's take a simple example, mineral wool has the following vapor permeability coefficient: µ=1. This means that the material passes moisture as well as air. And if we take aerated concrete, then its µ will be equal to 10, that is, its vapor conductivity is ten times worse than that of air.
Peculiarities
On the one hand, vapor permeability has a good effect on the microclimate, and on the other hand, it destroys the materials from which houses are built. For example, “cotton wool” perfectly passes moisture, but in the end, due to excess steam, condensation can form on windows and pipes with cold water, as the table also says. Because of this, the insulation loses its qualities. Professionals recommend installing a vapor barrier layer on the outside of the house. After that, the insulation will not let steam through. 
If the material has a low vapor permeability, then this is only a plus, because the owners do not have to spend money on insulating layers. And to get rid of the steam generated from cooking and hot water, the hood and the window will help - this is enough to maintain a normal microclimate in the house. In the case when the house is built of wood, it is impossible to do without additional insulation, while wood materials require a special varnish.
The table, graph and diagram will help you understand the principle of this property, after which you can already decide on the choice of a suitable material. Also, do not forget about the climatic conditions outside the window, because if you live in a zone with high humidity, then you should forget about materials with a high vapor permeability.
The concept of "breathing walls" is considered a positive characteristic of the materials from which they are made. But few people think about the reasons that allow this breathing. Materials capable of passing both air and steam are vapor-permeable.
A good example of building materials with high vapor permeability:
- wood;
- expanded clay slabs;
- foam concrete.
Concrete or brick walls are less permeable to steam than wood or expanded clay.
Sources of steam indoors
Human breathing, cooking, water vapor from the bathroom and many other sources of steam in the absence of an exhaust device create a high level of humidity indoors. You can often observe the formation of perspiration on window panes in winter, or on cold water pipes. These are examples of the formation of water vapor inside the house.
What is vapor permeability
The design and construction rules give the following definition of the term: the vapor permeability of materials is the ability to pass through moisture droplets contained in the air due to different partial vapor pressures from opposite sides at the same air pressure values. It is also defined as the density of the steam flow passing through a certain thickness of the material.
The table, which has a vapor permeability coefficient, compiled for building materials, is conditional, since the specified calculated values \u200b\u200bof humidity and atmospheric conditions do not always correspond to real conditions. The dew point can be calculated based on approximate data.
Wall construction taking into account vapor permeability
Even if the walls are built from a material with high vapor permeability, this cannot be a guarantee that it will not turn into water in the thickness of the wall. To prevent this from happening, it is necessary to protect the material from the difference in partial vapor pressure from inside and outside. Protection against the formation of steam condensate is carried out using OSB boards, insulating materials such as foam and vapor-tight films or membranes that prevent steam from penetrating into the insulation.
The walls are insulated in such a way that a layer of insulation is located closer to the outer edge, incapable of forming moisture condensation, pushing the dew point (water formation) away. In parallel with the protective layers in the roofing cake, it is necessary to ensure the correct ventilation gap.
The destructive action of steam
If the wall cake has a weak ability to absorb steam, it is not in danger of destruction due to the expansion of moisture from frost. The main condition is to prevent the accumulation of moisture in the thickness of the wall, but to ensure its free passage and weathering. It is equally important to arrange a forced extraction of excess moisture and steam from the room, to connect a powerful ventilation system. By observing the above conditions, you can protect the walls from cracking, and increase the life of the whole house. The constant passage of moisture through building materials accelerates their destruction.
Use of conductive qualities
Taking into account the peculiarities of the operation of buildings, the following principle of insulation is applied: the most steam-conducting insulation materials are located outside. Due to this arrangement of layers, the likelihood of water accumulation when the temperature drops outside is reduced. To prevent the walls from getting wet from the inside, the inner layer is insulated with a material having low vapor permeability, for example, a thick layer of extruded polystyrene foam.
The opposite method of using the steam-conducting effects of building materials is successfully applied. It consists in the fact that a brick wall is covered with a vapor barrier layer of foam glass, which interrupts the moving flow of steam from the house to the street during low temperatures. The brick begins to accumulate humidity in the rooms, creating a pleasant indoor climate thanks to a reliable vapor barrier.
Compliance with the basic principle when building walls
Walls should be characterized by a minimum ability to conduct steam and heat, but at the same time be heat-retaining and heat-resistant. When using one type of material, the desired effects cannot be achieved. The outer wall part is obliged to retain cold masses and prevent their impact on internal heat-intensive materials that maintain a comfortable thermal regime inside the room.
Reinforced concrete is ideal for the inner layer, its heat capacity, density and strength have maximum performance. Concrete successfully smooths out the difference between night and day temperature changes.
When carrying out construction work, wall cakes are made taking into account the basic principle: the vapor permeability of each layer should increase in the direction from the inner layers to the outer ones.
Rules for the location of vapor barrier layers
To ensure better performance of multilayer structures of buildings, the rule applies: on the side with a higher temperature, materials with increased resistance to steam penetration with increased thermal conductivity are placed. The layers located outside must have a high vapor conductivity. For the normal functioning of the building envelope, it is necessary that the coefficient of the outer layer is five times higher than the indicator of the layer located inside. 
When this rule is followed, it will not be difficult for water vapor that has entered the warm layer of the wall to quickly escape through more porous materials.
If this condition is not observed, the inner layers of building materials lock up and become more heat-conducting.
Familiarity with the table of vapor permeability of materials
When designing a house, the characteristics of building materials are taken into account. The Code of Practice contains a table with information on what vapor permeability coefficient building materials have under conditions of normal atmospheric pressure and average air temperature.
Material | Vapor permeability coefficient |
extruded polystyrene foam | |
polyurethane foam | |
mineral wool | |
reinforced concrete, concrete | |
pine or spruce | |
expanded clay | |
foam concrete, aerated concrete | |
granite, marble | |
drywall | |
chipboard, OSB, fiberboard | |
foam glass | |
ruberoid | |
polyethylene | |
linoleum |
The importance of the material vapor permeability table
The vapor permeability coefficient is an important parameter that is used to calculate the thickness of the layer of insulation materials. The quality of the insulation of the entire structure depends on the correctness of the results obtained.
Sergey Novozhilov is an expert in roofing materials with 9 years of practical experience in the field of engineering solutions in construction.
To create a climate favorable for living in a house, it is necessary to take into account the properties of the materials used. Particular attention should be paid to vapor permeability. This term refers to the ability of materials to pass vapor. Thanks to knowledge of vapor permeability, you can choose the right materials to create a house.
Equipment for determining the degree of permeability
Professional builders have specialized equipment that allows you to accurately determine the vapor permeability of a particular building material. The following equipment is used to calculate the described parameter:
- scales, the error of which is minimal;
- vessels and bowls necessary for conducting experiments;
- tools that allow you to accurately determine the thickness of the layers of building materials.
Thanks to such tools, the described characteristic is precisely determined. But the data on the results of the experiments are listed in the tables, so when creating a project at home, it is not necessary to determine the vapor permeability of materials.
What you need to know
Many are familiar with the opinion that "breathing" walls are beneficial for those living in the house. The following materials have high rates of vapor permeability:
- wood;
- expanded clay;
- cellular concrete.
It is worth noting that walls made of brick or concrete also have vapor permeability, but this figure is lower. During the accumulation of steam in the house, it is removed not only through the hood and windows, but also through the walls. That is why many believe that it is “hard” to breathe in buildings made of concrete and brick.
But it is worth noting that in modern homes, most of the steam leaves through the windows and the hood. At the same time, only about 5 percent of the steam escapes through the walls. It is important to know that in windy weather, heat leaves the building made of breathable building materials faster. That is why during the construction of a house, other factors that affect the preservation of the microclimate in the room should be taken into account.
It is worth remembering that the higher the vapor permeability coefficient, the more moisture the walls contain. The frost resistance of a building material with a high degree of permeability is low. When different building materials get wet, the vapor permeability index can increase up to 5 times. That is why it is necessary to competently fix the vapor barrier materials.
Influence of vapor permeability on other characteristics
It is worth noting that if no insulation was installed during construction, in severe frost in windy weather, heat from the rooms will leave quickly enough. That is why it is necessary to properly insulate the walls.
At the same time, the durability of walls with high permeability is lower. This is due to the fact that when steam enters the building material, moisture begins to solidify under the influence of low temperature. This leads to the gradual destruction of the walls. That is why, when choosing a building material with a high degree of permeability, it is necessary to correctly install a vapor barrier and heat-insulating layer. To find out the vapor permeability of materials, it is worth using a table in which all values \u200b\u200bare indicated.
Vapor permeability and wall insulation
During the insulation of the house, it is necessary to follow the rule according to which the vapor transparency of the layers should increase outward. Thanks to this, in winter there will be no accumulation of water in the layers if condensate begins to accumulate at the dew point.
It is worth insulating from the inside, although many builders recommend fixing heat and vapor barrier from the outside. This is due to the fact that steam penetrates from the room and when the walls are insulated from the inside, moisture will not enter the building material. Extruded polystyrene foam is often used for internal insulation of a house. The vapor permeability coefficient of such a building material is low.
Another way to insulate is to separate the layers with a vapor barrier. You can also use a material that does not let steam through. An example is the insulation of walls with foam glass. Despite the fact that the brick is able to absorb moisture, foam glass prevents the penetration of steam. In this case, the brick wall will serve as a moisture accumulator and, during fluctuations in the level of humidity, will become a regulator of the internal climate of the premises.
It is worth remembering that if the walls are not properly insulated, building materials may lose their properties after a short period of time. That is why it is important to know not only about the qualities of the components used, but also about the technology for fixing them on the walls of the house.
What determines the choice of insulation
Often homeowners use mineral wool for insulation. This material has a high degree of permeability. According to international standards, the vapor permeability resistance is 1. This means that mineral wool practically does not differ from air in this respect.
This is what many manufacturers of mineral wool mention quite often. You can often find a mention that when a brick wall is insulated with mineral wool, its permeability will not decrease. It really is. But it is worth noting that not a single material from which the walls are made is capable of removing such an amount of steam so that a normal level of humidity is maintained in the premises. It is also important to consider that many of the finishing materials that are used in the design of the walls in the rooms can completely isolate the space, without letting the steam out. Because of this, the vapor permeability of the wall is significantly reduced. That is why mineral wool has little effect on steam exchange.
The term "vapor permeability" itself indicates the property of materials to pass or retain water vapor in its thickness. The table of vapor permeability of materials is conditional, since the calculated values of the level of humidity and atmospheric action do not always correspond to reality. The dew point can be calculated according to the average value.
Each material has its own percentage of vapor permeability
Determining the level of steam permeability
In the arsenal of professional builders there are special technical tools that allow diagnosing the vapor permeability of a particular building material with high accuracy. To calculate the parameter, the following tools are used:
- devices that make it possible to accurately determine the thickness of the layer of building material;
- laboratory glassware for research;
- scales with the most accurate readings.
In this video you will learn about vapor permeability:
With the help of such tools, it is possible to correctly determine the desired characteristic. Since the experimental data are recorded in the tables of the vapor permeability of building materials, it is not necessary to establish the vapor permeability of building materials during the preparation of a dwelling plan.
Creation of comfortable conditions
To create a favorable microclimate in a dwelling, it is necessary to take into account the characteristics of the building materials used. Particular emphasis should be placed on vapor permeability. With knowledge of this ability of the material, it is possible to correctly select the raw materials necessary for housing construction. Data is taken from building codes and regulations, for example:
- vapor permeability of concrete: 0.03 mg/(m*h*Pa);
- vapor permeability of fiberboard, chipboard: 0.12-0.24 mg / (m * h * Pa);
- vapor permeability of plywood: 0.02 mg/(m*h*Pa);
- ceramic brick: 0.14-0.17 mg / (m * h * Pa);
- silicate brick: 0.11 mg / (m * h * Pa);
- roofing material: 0-0.001 mg / (m * h * Pa).
Steam generation in a residential building can be caused by human and animal breathing, food preparation, temperature differences in the bathroom, and other factors. No exhaust ventilation also creates a high degree of humidity in the room. In winter, it is often possible to notice the occurrence of condensate on windows and on cold pipelines. This is a clear example of the appearance of steam in residential buildings.
Protection of materials in the construction of walls
Building materials with high permeability steam cannot fully guarantee the absence of condensation inside the walls. In order to prevent the accumulation of water in the depths of the walls, the pressure difference of one of the components of the mixture of gaseous elements of water vapor on both sides of the building material should be avoided.
Provide protection from the appearance of liquid actually using oriented strand board (OSB), insulating materials such as foam and vapor barrier film or membrane that prevents steam from seeping into the thermal insulation. Simultaneously with the protective layer, it is required to organize the correct air gap for ventilation.
If the wall cake does not have sufficient capacity to absorb steam, it does not risk being destroyed as a result of the expansion of condensate from low temperatures. The main requirement is to prevent the accumulation of moisture inside the walls and provide its unhindered movement and weathering.
An important condition is the installation of a ventilation system with forced exhaust, which will not allow excess liquid and steam to accumulate in the room. By fulfilling the requirements, you can protect the walls from cracking and increase the durability of the home as a whole.
Location of thermal insulation layers
To ensure the best performance of the multi-layer structure of the structure, the following rule is used: the side with a higher temperature is provided with materials with increased resistance to steam infiltration with a high coefficient of thermal conductivity.
The outer layer must have high vapor conductivity. For the normal operation of the enclosing structure, it is necessary that the index of the outer layer is five times higher than the values of the inner layer. Subject to this rule, water vapor that has entered the warm layer of the wall will leave it without much effort through more cellular building materials. Neglecting these conditions, the inner layer of building materials becomes damp, and its thermal conductivity becomes higher.
The selection of finishes also plays an important role in the final stages of construction work. Properly selected composition of the material guarantees effective removal of liquid into the external environment, therefore, even at sub-zero temperatures, the material will not collapse.
The vapor permeability index is a key indicator when calculating the size of the cross section of the insulation layer. The reliability of the calculations made will depend on how high-quality the insulation of the entire building will turn out.