Comparison of different types of insulation. Vapor permeability of thermal insulation. Should insulation “breathe”? Which vapor permeability is better for insulation?
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 that can pass both air and steam are vapor permeable.
A clear 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.
Indoor steam sources
Human breathing, cooking, water vapor from the bathroom and many other sources of steam in the absence of an exhaust device create high levels of humidity indoors. You can often observe the formation of perspiration on window glass in winter time, or on cold water pipes. These are examples of water vapor forming inside a home.
What is vapor permeability
The design and construction rules give the following definition of the term: vapor permeability of materials is the ability to pass through droplets of moisture contained in the air due to different values of partial vapor pressures with 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 containing the coefficient of vapor permeability, compiled for building materials, is of a conditional nature, since the specified calculated values of humidity and atmospheric conditions do not always correspond to real conditions. The dew point can be calculated based on approximate data.
Wall design taking into account vapor permeability
Even if the walls are built from a material that has high vapor permeability, this cannot be a guarantee that it will not turn into water within the thickness of the wall. To prevent this from happening, you need 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 penoplex and vapor-proof films or membranes that prevent steam from penetrating into the insulation.
The walls are insulated so that closer to the outer edge there is a layer of insulation that is unable to form moisture condensation and pushes back the dew point (water formation). In parallel with the protective layers in the roofing pie, it is necessary to ensure the correct ventilation gap.
Destructive effects 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 moisture from accumulating 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, and connect a powerful ventilation system. By observing the above conditions, you can protect the walls from cracking and increase the service life of the entire house. The constant passage of moisture through building materials accelerates their destruction.
Use of conductive qualities
Taking into account the peculiarities of building operation, the following insulation principle is applied: the most vapor-conducting insulating materials are located outside. Thanks to this arrangement of layers, the likelihood of water accumulating when the outside temperature drops is reduced. To prevent the walls from getting wet from the inside, the inner layer is insulated with a material that has low vapor permeability, for example, thick layer extruded polystyrene foam.
The opposite method of using the vapor-conducting effects of building materials has been successfully used. It consists of covering a brick wall 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 moisture in the rooms, creating a pleasant indoor climate thanks to a reliable vapor barrier.
Compliance with the basic principle when constructing walls
The walls must have a minimum ability to conduct steam and heat, but at the same time be heat-intensive and heat-resistant. When using one type of material, the required effects cannot be achieved. The outer wall part must retain cold masses and prevent their impact on internal heat-intensive materials that maintain a comfortable thermal regime inside the room.
Ideal for inner layer reinforced concrete, its heat capacity, density and strength have maximum indicators. Concrete successfully smoothes out the difference between night and day temperature changes.
When conducting construction work make up wall pies 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 characteristics of multi-layer building structures, the rule is applied: on the side with a higher temperature, materials with increased resistance to steam penetration with increased thermal conductivity are placed. Layers located on the outside must have high vapor conductivity. For normal functioning The enclosing structure requires that the coefficient of the outer layer is five times higher than that of the layer located inside.
If this rule is followed, it will not be difficult for water vapor trapped in the warm layer of the wall to quickly escape through more porous materials.
If this condition is not met, the inner layers of building materials harden and become more thermally conductive.
Introduction to the table of vapor permeability of materials
When designing a house, the characteristics of building materials are taken into account. The Code of Rules contains a table with information about what coefficient of vapor permeability building materials have under normal conditions. atmospheric pressure and average air temperature.
| Material | Vapor permeability coefficient mg/(m h Pa) |
| extruded polystyrene foam | |
| polyurethane foam | |
| mineral wool | |
| reinforced concrete, concrete | |
| pine or spruce | |
| expanded clay | |
| foam concrete, aerated concrete | |
| granite, marble | |
| drywall | |
| chipboard, osp, fibreboard | |
| foam glass | |
| roofing felt | |
| polyethylene | |
| linoleum |
The importance of the table of vapor permeability of materials
The vapor permeability coefficient is an important parameter that is used to calculate the layer thickness insulation materials. The quality of insulation of the entire structure depends on the correctness of the results obtained.
Sergey Novozhilov - expert on roofing materials with 9 years experience practical work in area engineering solutions in construction.
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Movement of water vapor
- foam concrete;
- aerated concrete;
- perlite concrete;
- expanded clay concrete.
Aerated concrete
The right finish
Expanded clay concrete
Structure of expanded clay concrete
Polystyrene concrete
rusbetonplus.ru
Vapor permeability of concrete: features of the properties of aerated concrete, expanded clay concrete, polystyrene concrete
Often in construction articles there is an expression - vapor permeability concrete walls. It means the material’s ability to pass water vapor, or, in popular parlance, “breathe.” This parameter has great importance, since waste products are constantly formed in the living room, which must be constantly removed outside.
The photo shows moisture condensation on building materials
General information
If you do not create normal ventilation in the room, dampness will be created in it, which will lead to the appearance of fungus and mold. Their secretions can be harmful to our health.
Movement of water vapor
On the other hand, vapor permeability affects the ability of a material to accumulate moisture. This is also a bad indicator, since the more it can retain it, the higher the likelihood of fungus, putrefactive manifestations, and damage due to freezing.
Improper removal of moisture from the room
Vapor permeability is denoted by the Latin letter μ and measured in mg/(m*h*Pa). The value indicates the amount of water vapor that can pass through wall material on an area of 1 m2 and with a thickness of 1 m in 1 hour, as well as the difference in external and internal pressure 1 Pa.
High ability to conduct water vapor in:
- foam concrete;
- aerated concrete;
- perlite concrete;
- expanded clay concrete.
Heavy concrete closes the table.
Advice: if you need to make a technological channel in the foundation, this will help you diamond drilling holes in concrete.
Aerated concrete
- Using the material as an enclosing structure makes it possible to avoid the accumulation of unnecessary moisture inside the walls and preserve its heat-saving properties, which will prevent possible destruction.
- Any aerated concrete and foam concrete block contains ≈ 60% air, due to which the vapor permeability of aerated concrete is recognized as good, the walls in this case can “breathe”.
- Water vapor seeps freely through the material, but does not condense in it.
The vapor permeability of aerated concrete, as well as foam concrete, is significantly superior to heavy concrete - for the first it is 0.18-0.23, for the second - (0.11-0.26), for the third - 0.03 mg/m*h* Pa.
The right finish
I would especially like to emphasize that the structure of the material provides it with effective removal of moisture from environment, so that even when the material freezes, it does not collapse - it is forced out through open pores. Therefore, preparing the finish aerated concrete walls, you should take this feature into account and select the appropriate plasters, putties and paints.
The instructions strictly regulate that their vapor permeability parameters are not lower than aerated concrete blocks used for construction.
Textured facade vapor-permeable paint for aerated concrete
Tip: do not forget that vapor permeability parameters depend on the density of aerated concrete and may differ by half.
For example, if you use concrete blocks with density D400 - their coefficient is 0.23 mg/m h Pa, and for D500 it is already lower - 0.20 mg/m h Pa. In the first case, the numbers indicate that the walls will have a higher “breathing” ability. So when selecting finishing materials for walls made of D400 aerated concrete, make sure that their vapor permeability coefficient is the same or higher.
Otherwise, this will lead to poor drainage of moisture from the walls, which will affect the level of living comfort in the house. You should also take into account that if you used vapor-permeable paint for aerated concrete for the exterior, and non-vapor-permeable materials for the interior, the steam will simply accumulate inside the room, making it damp.
Expanded clay concrete
The vapor permeability of expanded clay concrete blocks depends on the amount of filler in its composition, namely expanded clay - foamed baked clay. In Europe, such products are called eco- or bioblocks.
Advice: if you cannot cut the expanded clay block with a regular circle and grinder, use a diamond one. For example, cutting reinforced concrete with diamond wheels makes it possible to quickly solve the problem.
Structure of expanded clay concrete
Polystyrene concrete
The material is another representative cellular concrete. The vapor permeability of polystyrene concrete is usually equal to that of wood. You can make it yourself.
What does the structure of polystyrene concrete look like?
Today, more attention is beginning to be paid not only to thermal properties wall structures, and also the comfort of living in the building. In terms of thermal inertness and vapor permeability, polystyrene concrete resembles wooden materials, and heat transfer resistance can be achieved by changing its thickness. Therefore, poured monolithic polystyrene concrete is usually used, which is cheaper than ready-made slabs.
Conclusion
From the article you learned that building materials have such a parameter as vapor permeability. It makes it possible to remove moisture outside the walls of the building, improving their strength and characteristics. Vapor permeability of foam concrete and aerated concrete, as well as heavy concrete differs in its performance, which must be taken into account when choosing finishing materials. The video in this article will help you find additional information on this topic.
Page 2
During operation, a variety of defects may occur. iron concrete structures. At the same time, it is very important to identify problem areas in a timely manner, localize and eliminate damage, since a significant part of them is prone to expansion and aggravation of the situation.
Below we will look at the classification of main defects concrete covering, and also provide a number of tips for repairing it.
During the operation of reinforced concrete products, various damages appear on them.
Factors that influence strength
Before analyzing common defects in concrete structures, it is necessary to understand what may be causing them.
The key factor here will be the strength of the hardened concrete solution, which is determined by the following parameters:
The closer the solution composition is to the optimal one, the less problems will be in operation of the structure
- Composition of concrete. The higher the grade of cement included in the solution, and the stronger the gravel that was used as filler, the more durable the coating or monolithic design. Naturally, when using high-quality concrete, the price of the material increases, so in any case we need to look for a compromise between economy and reliability.
Note! Excessively strong compositions are very difficult to process: for example, to perform the simplest operations, expensive cutting of reinforced concrete with diamond wheels may be required.
That's why you shouldn't overdo it with the selection of materials!
- Reinforcement quality. Along with high mechanical strength Concrete is characterized by low elasticity, therefore, when exposed to certain loads (bending, compression), it can crack. To avoid this, steel reinforcement is placed inside the structure. How stable the entire system will be depends on its configuration and diameter.
For sufficiently strong compositions, diamond drilling of holes in concrete is required: regular drill"Won't take it"!
- Surface permeability. If the material is characterized by a large number of pores, then sooner or later moisture will penetrate into them, which is one of the most destructive factors. Temperature changes at which the liquid freezes, destroying the pores due to an increase in volume, have a particularly detrimental effect on the condition of the concrete coating.
In principle, it is the listed factors that are decisive for ensuring the strength of cement. However, even in an ideal situation, sooner or later the coating is damaged, and we have to restore it. What can happen in this case and how we need to act will be discussed below.
Mechanical damage
Chips and cracks
Detection of deep damage using a flaw detector
The most common defects are mechanical damage. They can arise due to various factors, and are conventionally divided into external and internal. And if a special device is used to determine internal ones - a concrete flaw detector, then problems on the surface can be seen independently.
The main thing here is to determine the reason why the malfunction occurred and promptly eliminate it. For ease of analysis, we have structured examples of the most common damage in the form of a table:
| Defect | |
| Potholes on the surface | Most often they occur due to shock loads. It is also possible for potholes to form in areas of prolonged exposure to significant mass. |
| Chips | They are formed by mechanical influence on areas under which zones of low density are located. They are almost identical in configuration to potholes, but usually have less depth. |
| Peeling | Represents the separation of the surface layer of the material from the main mass. Most often it occurs due to poor drying of the material and finishing before the solution is completely hydrated. |
| Mechanical cracks | They occur with prolonged and intense exposure to a large area. Over time, they expand and connect with each other, which can lead to the formation of large potholes. |
| Bloating | Formed if surface layer compacted until air is completely removed from the solution mass. Also, the surface swells when treated with paint or impregnations (sealings) of undried cement. |
Photo of a deep crack
As can be seen from the analysis of the causes, the occurrence of some of the listed defects could have been avoided. But mechanical cracks, chips and potholes are formed due to the use of the coating, so they simply need to be repaired periodically. Instructions for prevention and repair are given in the next section.
Prevention and repair of defects
To minimize the risk of mechanical damage, first of all you need to follow the technology for arranging concrete structures.
Of course, this question has many nuances, so we will give only the most important rules:
- Firstly, the class of concrete must correspond to the design loads. Otherwise, saving on materials will lead to the fact that the service life will be reduced significantly, and you will have to spend effort and money on repairs much more often.
- Secondly, you need to follow the pouring and drying technology. The solution requires high-quality compaction of concrete, and when hydrated, the cement should not lack moisture.
- It is also worth paying attention to the timing: without the use of special modifiers, surfaces cannot be finished earlier than 28-30 days after pouring.
- Thirdly, the coating should be protected from excessively intense impacts. Of course, loads will affect the condition of concrete, but we can reduce the damage from them.
Vibration compaction increases strength significantly
Note! Even simply limiting the speed of traffic in problem areas leads to the fact that defects in the asphalt concrete pavement occur much less frequently.
Another important factor is the timeliness of repairs and compliance with its methodology.
Here you need to follow a single algorithm:
- We clean the damaged area from fragments of the solution that have broken off from the main mass. For small defects you can use brushes, but large chips and cracks are usually cleaned compressed air or sandblaster.
- Using a concrete saw or hammer drill, we open up the damage, deepening it to a durable layer. If we are talking about a crack, then it must not only be deepened, but also widened to facilitate filling with the repair compound.
- We prepare a mixture for restoration using either a polyurethane-based polymer complex or non-shrinking cement. When eliminating large defects, so-called thixotropic compounds are used, and small cracks are best sealed with a casting agent.
Filling open cracks with thixotropic sealants
- We apply the repair mixture to the damage, then level the surface and protect it from loads until the product has completely polymerized.
In principle, these works are easy to do with your own hands, so we can save on hiring craftsmen.
Operational damage
Drawdowns, dust and other malfunctions
Cracks on a subsiding screed
Experts classify so-called operational defects into a separate group. These include the following:
| Defect | Characteristics and possible cause |
| Screed deformation | It is expressed in a change in the level of the poured concrete floor (most often the coating sinks in the center and rises at the edges). Can be caused by several factors: · Uneven density of the base due to insufficient compaction. · Defects in the compaction of the mortar. · Difference in moisture content of the top and bottom layers of cement. · Insufficient reinforcement thickness. |
| Cracking | In most cases, cracks do not arise from mechanical stress, but from deformation of the structure as a whole. It can be triggered by both excessive loads exceeding the design ones and thermal expansion. |
| Peeling | Peeling of small scales on the surface usually begins with the appearance of a network of microscopic cracks. In this case, the cause of peeling is most often the accelerated evaporation of moisture from the outer layer of the solution, which leads to insufficient hydration of the cement. |
| Surface dusting | It is expressed in the constant formation of fine cement dust on concrete. May be caused by: · Lack of cement in the solution. · Excess moisture during pouring. · Water entering the surface during grouting. · Insufficiently high-quality cleaning of gravel from the dust fraction. · Excessive abrasive effect on concrete. |
Peeling of the surface
All of the above disadvantages arise either due to a violation of technology or due to improper operation of the concrete structure. However, eliminating them is somewhat more difficult than mechanical defects.
- Firstly, the solution must be poured and processed according to all the rules, preventing it from stratifying and peeling when dried.
- Secondly, the base needs to be prepared equally well. The more densely we compact the soil under a concrete structure, the less likely it will be to subsidence, deformation and cracking.
- To prevent poured concrete from cracking, a damper tape is usually installed around the perimeter of the room to compensate for deformations. For the same purpose on screeds large area seams with polymer filling are installed.
- You can also avoid the appearance of surface damage by applying polymer-based strengthening impregnations to the surface of the material or “ironizing” the concrete with a flowing solution.
Surface treated with a protective compound
Chemical and climatic effects
A separate group of damages consists of defects that arise as a result of climatic exposure or a reaction to chemicals.
This may include:
- The appearance of streaks and light spots on the surface - so-called efflorescence. Typically, the cause of the formation of salt deposits is a violation of the humidity regime, as well as the ingress of alkalis and calcium chlorides into the solution.
Efflorescence formed due to excess moisture and calcium
Note! It is for this reason that in areas with highly carbonate soils, experts recommend using imported water to prepare the solution.
Otherwise, a whitish coating will appear within a few months after pouring.
- Destruction of the surface under the influence of low temperatures. When moisture enters porous concrete, the microscopic channels in the immediate vicinity of the surface gradually expand as water expands in volume by about 10-15% when it freezes. The more often freezing/thawing occurs, the more intense the solution will degrade.
- To combat this, special anti-frost impregnations are used, and the surface is also coated with compounds that reduce porosity.
Before repairs, the fittings must be cleaned and treated
- Finally, corrosion of reinforcement can also be included in this group of defects. Metal embeds begin to rust where they are exposed, which leads to a decrease in the strength of the material. To stop this process, before filling the damage with a repair compound, the reinforcing bars must be cleaned of oxides and then treated with an anti-corrosion compound.
Conclusion
The defects in concrete and reinforced concrete structures described above can manifest themselves in a variety of forms. Despite the fact that many of them look quite harmless, when the first signs of damage are detected, it is worth taking appropriate measures, otherwise the situation may worsen dramatically over time.
Well and in the best possible way To avoid such situations is to strictly adhere to the technology for arranging concrete structures. The information presented in the video in this article is another confirmation of this thesis.
masterabetona.ru
Vapor permeability of materials table
To create favorable microclimate indoors, it is necessary to take into account the properties of building materials. Today we will analyze one property - the 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.
Tables that cover almost all materials used for construction will help you understand the issue. After studying this material, you will know how to build a warm and reliable home.
Equipment
If we are talking about Prof. construction, it uses special equipment to determine vapor permeability. This is how the table that appears in this article appeared.
The following equipment is used today:
- Scales with minimal error - analytical type model.
- Vessels or bowls for conducting experiments.
- Tools with high level accuracy for determining the thickness of layers of building materials.
Understanding the property
There is an opinion that “breathing walls” are beneficial for the house and its inhabitants. But all builders think about this concept. “Breathable” is a material that, in addition to air, also allows steam to pass through - this is the water permeability of building materials. Foam concrete and 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.
This graph shows the resistance to permeation. The brick wall practically does not allow moisture to pass through or let in. Steam is released when taking a hot shower or cooking. Because of this, increased humidity is created in the house - a hood can correct the situation. You can find out that the vapors are not escaping anywhere by looking at the condensation on the pipes and sometimes on the windows. Some builders believe that if a house is built of brick or concrete, then it is “hard” to breathe in the house.
In fact, the situation is better - in modern home about 95% of the steam escapes through the vent and hood. And if the walls are made of “breathing” 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 allow moisture to pass through due to vinyl wallpaper. “Breathing” walls also have a significant drawback - in windy weather, heat leaves the home.
The table will help you compare materials and find out their vapor permeability indicator:
The higher the vapor permeability index, the more moisture the wall can absorb, which means that the material has low frost resistance. If you are going to build walls from foam concrete or aerated block, 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 high thermal conductivity, but if the gas block gets wet, the indicator will increase 5 times. But we are interested in another parameter: the liquid tends to expand when it freezes, and as a result, the walls collapse.
Vapor permeability in multilayer construction
The sequence of layers and the type of insulation are what primarily affect vapor permeability. In the diagram below you can see that if the insulation material is located on the facade side, then the indicator of pressure on moisture saturation is lower.
The figure demonstrates in detail the effect of pressure and the penetration of steam into the material. If the insulation is located with inside at home, then between load-bearing structure and this construction will cause condensation. It negatively affects the entire microclimate in the house, while the destruction of building materials occurs much faster.
Let's understand the coefficient
The table becomes clear if you look at the coefficient. The coefficient in this indicator determines the amount of vapor, measured in grams, that passes through materials 1 meter thick and a layer of 1 m² within one hour. The ability to transmit or retain moisture characterizes the resistance to vapor permeability, which is indicated in the table by the symbol “µ”.
In simple words, coefficient is the resistance of building materials, comparable to the permeability of air. Let's look at a simple example: mineral wool has the following vapor permeability coefficient: µ=1. This means that the material allows moisture to pass through as well as air. And if you 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 the house is built. For example, “cotton wool” perfectly allows moisture to pass through, but in the end, due to excess steam on windows and pipes, cold water Condensation may form, as indicated in the table. Because of this, the insulation loses its quality. Professionals recommend installing a vapor barrier layer on the outside of the house. After this, the insulation will not allow steam to pass through.
Vapor permeation resistance If the material has a low vapor permeability rate, then this is only a plus, because the owners do not have to spend money on insulating layers. And get rid of the steam generated from cooking and hot water, a hood and a window will help - this is enough to maintain a normal microclimate in the house. When a house is built from wood, it is impossible to do without additional insulation, and wood materials require a special varnish.
The table, graph and diagram will help you understand the principle of operation of this property, after which you can already make your choice suitable material. Also, do not forget about climatic conditions outside the window, because if you live in an area with high humidity, then you should completely forget about materials with a high vapor permeability rate.
To create a favorable indoor microclimate, it is necessary to take into account the properties of building materials. Today we will look at 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.
Tables that cover almost all materials used for construction will help you understand the issue. After studying this material, you will know how to build a warm and reliable home.
Equipment
If we are talking about Prof. construction, it uses special equipment to determine vapor permeability. This is how the table that appears in this article appeared.
The following equipment is used today:
- Scales with minimal error - analytical type model.
- Vessels or bowls for conducting experiments.
- Instruments with a high level of accuracy for determining the thickness of layers of building materials.
Understanding the property
There is an opinion that “breathing walls” are beneficial for the house and its inhabitants. But all builders think about this concept. “Breathable” is a material that, in addition to air, also allows steam to pass through - this is the water permeability of building materials. Foam concrete and 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 - a hood can correct the situation. You can find out that the vapors are not escaping anywhere by looking at the condensation on the pipes and sometimes on the windows. Some builders believe that if a house is built of brick or concrete, then it is “hard” to breathe in the house.
In reality, the situation is better - in a modern home, about 95% of the steam escapes through the window and hood. And if the walls are made of “breathing” building materials, then 5% of the steam escapes through them. So residents of houses made of concrete or brick do not suffer much from this parameter. Also, the walls, regardless of the material, will not allow moisture to pass through due to vinyl wallpaper. “Breathing” walls also have a significant drawback - in windy weather, heat leaves the home.
The table will help you compare materials and find out their vapor permeability indicator:
The higher the vapor permeability index, the more moisture the wall can absorb, which means that the material has low frost resistance. If you are going to build walls from foam concrete or aerated block, 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 high thermal conductivity, but if the gas block gets wet, the indicator will increase 5 times. But we are interested in another parameter: the liquid tends to expand when it freezes, and as a result, the walls collapse.
Vapor permeability in multilayer construction
The sequence of layers and the type of insulation are what primarily affect vapor permeability. In the diagram below you can see that if the insulation material is located on the facade side, then the indicator of 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 structure. It negatively affects the entire microclimate in the house, while the destruction of building materials occurs much faster.
Let's understand the coefficient
The coefficient in this indicator determines the amount of vapor, measured in grams, that passes through materials 1 meter thick and a layer of 1 m² within one hour. The ability to transmit 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 look at a simple example: mineral wool has the following vapor permeability coefficient: µ=1. This means that the material allows moisture to pass through as well as air. And if you 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 the house is built. For example, “cotton wool” perfectly allows moisture to pass through, but as a result, due to excess steam, condensation can form on windows and pipes with cold water, as the table shows. Because of this, the insulation loses its quality. Professionals recommend installing a vapor barrier layer on the outside of the house. After this, the insulation will not allow steam to pass through. 
If the material has a low vapor permeability rate, then this is only a plus, because the owners do not have to spend money on insulating layers. And a hood and a window will help get rid of the steam generated from cooking and hot water - this is enough to maintain a normal microclimate in the house. When a house is built from wood, it is impossible to do without additional insulation, and wood materials require a special varnish.
The table, graph and diagram will help you understand the principle of operation 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 an area with high humidity, then you should completely forget about materials with a high vapor permeability rate.
First, let’s refute the misconception - it is not the fabric that “breathes,” but our body. More precisely, the surface of the skin. Man is one of those animals whose body strives to maintain a constant body temperature, regardless of conditions. external environment. One of the most important mechanisms of our thermoregulation is the sweat glands hidden in the skin. They are also part of the body's excretory system. The sweat they produce, evaporating from the surface of the skin, carries with it some of the excess heat. Therefore, when we are hot, we sweat to avoid overheating.
However, this mechanism has one serious drawback. Moisture, quickly evaporating from the surface of the skin, can cause hypothermia, which leads to colds. Of course, in Central Africa, where man has evolved as a species, such a situation is rather rare. But in regions with changeable and predominantly cool weather, a person constantly had and still has to supplement his natural thermoregulation mechanisms with various clothes.
The ability of clothing to “breathe” implies its minimal resistance to the removal of vapors from the surface of the skin and the “ability” to transport them to the front side of the material, where the moisture released by a person can evaporate without “stealing” the excess amount of heat. Thus, the “breathable” material from which the clothing is made helps the human body maintain optimal temperature body, avoiding overheating or hypothermia.
The “breathable” properties of modern fabrics are usually described in terms of two parameters - “vapor permeability” and “air permeability”. What is the difference between them and how does this affect their use in clothing for sports and active rest?
What is vapor permeability?
Vapor permeability is the ability of a material to transmit or retain water vapor. In the outdoor apparel and equipment industry, a material's high ability to water vapor transport. The higher it is, the better, because... This allows the user to avoid overheating and still remain dry.
All fabrics and insulation materials used today have a certain vapor permeability. However, in numerical terms it is presented only to describe the properties of membranes used in the production of clothing, and for a very small number not waterproof textile materials. Most often, vapor permeability is measured in g/m²/24 hours, i.e. the amount of water vapor that passes through a square meter of material per day.
This parameter is indicated by the abbreviation MVTR (“moisture vapor transmission rate” or “speed of passage of water vapor”).
The higher the value, the greater the vapor permeability of the material.
How is vapor permeability measured?
MVTR numbers are obtained from laboratory tests based on various techniques. Due to big amount variables affecting the operation of the membrane - individual metabolism, air pressure and humidity, area of material suitable for moisture transport, wind speed, etc.; there is no single standardized research method for determining vapor permeability. Therefore, in order to be able to compare samples of fabrics and membranes with each other, manufacturers of materials and finished clothing use whole line techniques. Each of them separately describes the vapor permeability of a fabric or membrane in a certain range of conditions. Today, the following test methods are most often used:
"Japanese" "upright cup" test (JIS L 1099 A-1)
The test sample is stretched and sealed on top of a cup, inside of which a strong desiccant - calcium chloride (CaCl2) - is placed. The cup is placed for a certain time in a thermohydrostat, in which the air temperature is maintained at 40°C and humidity at 90%.
Depending on how the weight of the desiccant changes during the control time, MVTR is determined. The technique is well suited for determining vapor permeability not waterproof fabrics, because the test sample is not in direct contact with water.
"Japanese" inverted cup test (JIS L 1099 B-1)
The test sample is stretched and hermetically fixed over a vessel with water. Afterwards it is turned over and placed over a cup with a dry desiccant - calcium chloride. After the control time, the desiccant is weighed, resulting in the calculation of MVTR.
Test B-1 is the most popular, as it demonstrates the highest numbers among all methods that determine the rate of passage of water vapor. Most often, it is its results that are published on labels. The most “breathable” membranes have an MVTR value according to the B1 test greater than or equal to 20,000 g/m²/24h according to test B1. Fabrics with values of 10-15,000 can be classified as noticeably vapor permeable, at least under not very intense loads. Finally, for clothing that requires little movement, a vapor permeability of 5-10,000 g/m²/24h is often sufficient.
The JIS L 1099 B-1 test method fairly accurately illustrates the performance of the membrane under ideal conditions (when there is condensation on its surface and moisture is transported to a drier environment with a lower temperature).
Sweating plate test or RET (ISO - 11092)
Unlike tests that determine the rate of water vapor transport through a membrane, the RET technique examines how much the test sample resists passage of water vapor.
A sample of fabric or membrane is placed on top of a flat porous metal plate, under which a heating element is connected. The plate temperature is maintained at the surface temperature of human skin (about 35°C). Water evaporating from heating element, passes through the plate and the test sample. This leads to heat loss on the surface of the plate, the temperature of which must be maintained constant. Accordingly, the higher the level of energy consumption to maintain a constant plate temperature, the lower the resistance of the tested material to the passage of water vapor through it. This parameter is designated as RET (Resistance of Evaporation of a Textile - “material resistance to evaporation”). The lower the RET value, the higher the breathability of the membrane or other material being tested.
- RET 0-6 - extremely breathable;
RET 6-13 - highly breathable; RET 13-20 - breathable; RET over 20 - non-breathable.
Equipment for carrying out the ISO-11092 test. On the right is a chamber with a “sweating plate”. A computer is required to obtain and process results and control the test procedure © thermetrics.com
In the laboratory of the Hohenstein Institute, with which Gore-Tex collaborates, this technique is complemented by testing real clothing samples by people on a treadmill. In this case, the results of the sweat plate tests are adjusted according to the testers' comments.
Testing Gore-Tex clothing on the treadmill © goretex.com
The RET test clearly illustrates the performance of the membrane in real conditions, but is also the most expensive and time-consuming on the list. For this reason, not all active clothing manufacturing companies can afford it. At the same time, RET is today the main method for assessing the vapor permeability of membranes from the Gore-Tex company.
The RET technique generally correlates well with the results of the B-1 test. In other words, a membrane that shows good breathability in the RET test will show good breathability in the inverted cup test.
Unfortunately, none of the test methods can replace the others. Moreover, their results do not always correlate with each other. We saw that the process of determining the vapor permeability of materials in various methods has many differences, simulating different conditions work.
In addition, different membrane materials operate on different principles. For example, porous laminates provide relatively free passage of water vapor through the microscopic pores present in their thickness, and non-porous membranes transport moisture to the front surface like a blotter - with the help of hydrophilic polymer chains in their structure. It is quite natural that one test can simulate the advantageous conditions for the operation of a pore-free membrane film, for example, when moisture adheres closely to its surface, and the other for microporous.
Taken together, all this means that there is practically no point in comparing materials with each other based on data obtained from different test methods. It also makes no sense to compare the vapor permeability of different membranes if the test method for at least one of them is unknown.
What is breathability?
Breathability- the ability of a material to pass air through itself under the influence of its pressure difference. When describing the properties of clothing, a synonym for this term is often used - “breathability”, i.e. how windproof the material is.
In contrast to methods for assessing vapor permeability, relative uniformity reigns in this area. To assess air permeability, the so-called Fraser test is used, which determines how much air will pass through the material during a control time. The test air flow rate is typically 30 mph, but may vary.
The unit of measurement is the cubic foot of air passing through the material in one minute. Denoted by the abbreviation CFM (cubic feet per minute).
The higher the value, the higher the air permeability (“blowability”) of the material. Thus, poreless membranes demonstrate absolute “windproofness” - 0 CFM. Test methods most often determined by ASTM D737 or ISO 9237 standards, which, however, give identical results.
Exact numbers CFMs are published relatively rarely by textile and ready-to-wear manufacturers. Most often, this parameter is used to characterize windproof properties in descriptions various materials, developed and used within the production of SoftShell clothing.
Recently, manufacturers have begun to “remember” air permeability much more often. The fact is that, along with the air flow, much more moisture evaporates from the surface of our skin, which reduces the risk of overheating and condensation accumulation under clothes. Thus, the Polartec Neoshell membrane has slightly greater air permeability than traditional pore membranes (0.5 CFM versus 0.1). Thanks to this, Polartec was able to achieve significant better work of its material in conditions of windy weather and rapid user movement. The higher the air pressure outside, the better Neoshell removes water vapor from the body due to greater air exchange. At the same time, the membrane continues to protect the user from wind cooling, blocking about 99% of the air flow. This turns out to be enough to withstand even stormy winds, and therefore Neoshell has even found itself in the production of single-layer assault tents (a striking example is the BASK Neoshell and Big Agnes Shield 2 tents).
But progress does not stand still. Today there are many offers of well-insulated mid-layers with partial breathability, which can also be used as an independent product. They use either fundamentally new insulation - like Polartec Alpha, or use synthetic volumetric insulation with a very low degree of fiber migration, which allows the use of less dense “breathable” fabrics. Thus, Sivera Gamayun jackets use ClimaShield Apex, Patagonia NanoAir uses insulation under the FullRange™ trademark, which is produced by the Japanese company Toray under the original name 3DeFX+. Identical insulation is used in Mountain Force ski jackets and trousers as part of the “12 way stretch” technology and Kjus ski clothing. The relatively high breathability of the fabrics in which these insulations are enclosed makes it possible to create an insulating layer of clothing that will not interfere with the removal of evaporated moisture from the surface of the skin, helping the user to avoid both getting wet and overheating.
SoftShell clothing. Subsequently, other manufacturers created an impressive number of their analogues, which led to the widespread use of thin, relatively durable, “breathable” nylon in clothing and equipment for sports and outdoor activities.
To create a climate favorable for living in your home, you need 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 vapors. Thanks to knowledge about vapor permeability, you can choose the right materials to create a home.
Equipment for determining the degree of permeability
Professional builders have specialized equipment, which allows you to accurately determine the vapor permeability of a certain building material. To calculate the described parameter, the following equipment is used:
- scales whose error is minimal;
- vessels and bowls necessary for conducting experiments;
- tools that allow you to accurately determine the thickness of layers of building materials.
Thanks to such tools, the described characteristic is accurately determined. But the data on the results of the experiments are entered into tables, so when creating a house project it is not necessary to determine the vapor permeability of materials.
What you need to know
Many people are familiar with the opinion that “breathable” walls are beneficial for those living in the house. The following materials have high vapor permeability rates:
- tree;
- expanded clay;
- cellular concrete.
It is worth noting that walls made of brick or concrete also have vapor permeability, but this indicator is lower. When steam accumulates in the house, it is released not only through the hood and windows, but also through the walls. This is why many people believe that it is “hard to breathe” in buildings made of concrete and brick.
But it is worth noting that in modern houses Most of the steam escapes through the windows and 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 escapes faster from a building made of breathable building materials. That is why, during the construction of a house, other factors affecting the preservation of the indoor microclimate should be taken into account.
It is worth remembering that the higher the vapor permeability coefficient, the more wall contain moisture. The frost resistance of building materials with a high degree of permeability is low. When different building materials get wet, the vapor permeability rate can increase up to 5 times. That is why it is necessary to correctly secure vapor barrier materials.
The influence of vapor permeability on other characteristics
It is worth noting that if insulation was not installed during construction, in severe frost and windy weather the heat will leave the rooms quite quickly. That is why it is necessary to properly insulate walls.
At the same time, the durability of walls with high permeability is lower. This is due to the fact that when steam enters a building material, the 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 thermal insulation layer. To find out the vapor permeability of materials, you should use a table that shows all the values.
Vapor permeability and wall insulation
When insulating a house, it is necessary to follow the rule that the vapor transparency of the layers should increase towards the outside. Thanks to this, in winter there will be no accumulation of water in the layers if condensation 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 explained by the fact that steam penetrates from the room and when insulating the walls 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 building material is low.
Another method of insulation is to separate the layers using a vapor barrier. You can also use a material that does not allow steam to pass through. An example is the insulation of walls with foam glass. Despite the fact that 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 humidity levels, will become a regulator of the internal climate of the premises.
It is worth remembering that if you insulate the walls incorrectly, 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 home owners use mineral wool for insulation. This material has a high degree of permeability. By international standards vapor permeability resistance is 1. This means that mineral wool in this respect is practically no different from air.
This is what many mineral wool manufacturers mention quite often. You can often find mention that when insulating a brick wall with mineral wool, its permeability will not decrease. This is true. But it is worth noting that not a single material from which 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 finishing materials that are used to decorate walls in rooms can completely isolate the space without allowing steam to escape. Because of this, the vapor permeability of the wall is significantly reduced. This is why mineral wool has little effect on steam exchange.
First of all, it must be said that I will not talk about vapor-permeable (breathable) and vapor-impermeable (non-breathable) walls in terms of good/bad, but will consider them as two alternative options. Each of these options is completely correct if fulfilled with all the required requirements. That is, I do not answer the question “are vapor-permeable walls necessary,” but consider both options.
So, vapor-permeable walls breathe and allow air (steam) to pass through them, but vapor-impermeable walls do not breathe and do not allow air (steam) to pass through them. Vapor-permeable walls are made only from vapor-permeable materials. Vapor-impermeable walls contain in their design at least one layer of vapor-impermeable material (this is enough for the entire wall to become vapor-impermeable). All materials are divided into vapor-permeable and non-vapor-permeable, this is not good, not bad - this is such a given :-).
Now let's see what all this means when these walls are included in real house(apartment). We do not consider the constructive capabilities of vapor-permeable and vapor-impermeable walls in this matter. Both such and such a wall can be made strong, rigid, etc. The main differences arise in these two questions:
Heat loss. Naturally, additional heat loss occurs through vapor-permeable walls (heat also leaves along with the air). It must be said that these heat losses are very small (5-7% of the total). Their size affects the thickness of the thermal insulation and heating power. When calculating the thickness (of the wall, if it is without insulation, or the insulation itself), the vapor permeability coefficient is taken into account. When calculating heat loss for heating selection, heat loss due to the vapor permeability of the walls is also taken into account. That is, these losses are not lost anywhere, they are taken into account when calculating what they affect. And, moreover, we have already made enough such calculations (based on the thickness of the insulation and heat loss to calculate the heating power), and this is what can be seen: there is a difference in the numbers, but it is so small that it really cannot affect either the thickness of the insulation or the power heating device. Let me explain: if for a vapor-permeable wall you need, for example, 43 mm of insulation, and for a non-vapor-permeable wall, 42 mm, then it is still 50 mm, in both versions. The same is with the boiler power, if based on the overall heat loss, it is clear that a 24 kW boiler is needed, for example, then just because of the vapor permeability of the walls, the next most powerful boiler will not work.
Ventilation. Vapor-permeable walls participate in air exchange in the room, but vapor-permeable walls do not. The room must have inflow and exhaust, they must correspond to the norm and be approximately equal. In order to understand how much supply and exhaust there should be in a house/apartment (in m3 per hour), a ventilation calculation is made. It takes into account all the possibilities of supply and exhaust, considers the norm for this house/apartment, compares the realities and the norm, and recommends methods for bringing the power of supply and exhaust to the norm. So this is what comes out as a result of these calculations (we have already done a lot of them): as a rule, in modern houses there is not enough inflow. This happens because modern windows are steam-tight. Previously, no one considered this ventilation for private housing, since the influx was normally provided by old wooden windows, leaky doors, walls with cracks, etc. And now, if we take new construction, almost all houses with plastic windows, and at least half with vapor-impermeable walls. And there is practically no (constant) air flow in such houses. Here you can see examples of ventilation calculations in the topics:
It is clear from these houses that the inflow through the walls (if they are vapor-permeable) will be only about 1/5 of the required inflow. That is, ventilation must be designed (calculated) normally no matter what the walls and windows are. Only vapor-permeable walls, and everything - necessary the influx is still not provided.
Sometimes the issue of vapor permeability of walls becomes relevant in such a situation. In an old house/apartment that lived normally with vapor-permeable walls, old wooden windows, and one exhaust duct in the kitchen, they begin to replace the windows (with plastic ones), then, for example, the walls are insulated with foam plastic (from the outside, as expected). Wet walls, mold, etc. begin. The ventilation stopped working. There is no inflow, without inflow the hood does not work. From here, it seems to me, arose the myth about the “terrible polystyrene foam”, which as soon as you insulate a wall, mold will immediately begin to grow. And the point here is a set of issues regarding ventilation and insulation, and not the “horror” of this or that material.
Regarding what you write, “it is impossible to make airtight walls.” This is not entirely true. It is quite possible to make them (with a certain approximation to tightness), and they are made. We are currently preparing an article about such houses, where windows/walls/doors are completely sealed, all air is supplied through a recovery system, etc. This is the principle of so-called “passive” houses, we will talk about this soon.
Thus, here is the conclusion: you can choose either a vapor-permeable wall or a non-vapor-permeable one. The main thing is to competently resolve all related issues: proper thermal insulation and compensation for heat loss, and ventilation.
