Often in construction articles there is an expression - vapor permeability concrete walls. It means the ability of the material to pass water vapor, in a popular way - "breathe". This setting has great importance, since waste products are constantly formed in the living room, which must be constantly brought out.
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.
On the other hand, vapor permeability affects the ability of the material to accumulate moisture in itself. This is also a bad indicator, since the more it can hold in itself, the higher the likelihood of fungus, putrefactive manifestations, and destruction during freezing.
Vapor permeability is denoted by the Latin letter μ and is measured in mg / (m * h * Pa). The value indicates the amount of water vapor that can pass through wall material on an area of \u200b\u200b1 m 2 and with a thickness of 1 m in 1 hour, as well as the difference in external and internal pressure 1 Pa.
High capacity for conducting water vapor in:
- foam concrete;
- aerated concrete;
- perlite concrete;
- expanded clay concrete.
Closes the table - heavy concrete.
Tip: if you need to make a technological channel in the foundation, it will help you diamond drilling holes in concrete.
aerated concrete
- The use of the material as a building envelope 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 foam concrete block has in its composition ≈ 60% of air, due to which the vapor permeability of aerated concrete is recognized at a good level, the walls in this case can "breathe".
- Water vapor freely seeps through the material, but does not condense in it.
The vapor permeability of aerated concrete, as well as foam concrete, significantly exceeds heavy concrete - for the first 0.18-0.23, for the second - (0.11-0.26), for the third - 0.03 mg / m * h * Pa.
I would especially like to emphasize that the structure of the material provides it with effective removal moisture in environment, so that even when the material freezes, it does not collapse - it is forced out through open pores. Therefore, when preparing, one should take into account this feature and select the appropriate plasters, putties and paints.
The instruction strictly regulates that their vapor permeability parameters are not lower than aerated concrete blocks used for construction.
Tip: do not forget that the vapor permeability parameters depend on the density of aerated concrete and may differ by half.
For example, if you use D400, they have a coefficient of 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 choosing finishing materials for D400 aerated concrete walls, make sure that their vapor permeability coefficient is the same or higher.
Otherwise, this will lead to a deterioration in the removal of moisture from the walls, which will affect the decrease in the comfort level of living in the house. It should also be noted that if you have been applied for exterior finish vapor-permeable paint for aerated concrete, and for interior - non-vapor-permeable materials, steam will simply accumulate inside the room, making it wet.
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.
Tip: if you can’t cut the expanded clay block with a regular circle and a grinder, use a diamond one.
For example, cutting reinforced concrete diamond circles makes it possible to quickly solve the problem.
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 with your own hands.
Today, more attention is being paid not only to the thermal properties of wall structures, but also to 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 finished 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. The 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 more information on this topic.
The concept of "breathing walls" is considered positive characteristic 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.
illustrative example 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 exhaust device create high level indoor humidity. You can often observe the formation of perspiration on window panes in winter time, 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 various sizes partial vapor pressures opposite sides at the same values air pressure. 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. Parallel to protective layers in 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. Equally important is to arrange forced exhaust excess moisture and steam from the room, 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 the period 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 external 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.
Perfect for the inner layer reinforced concrete, its heat capacity, density and strength have maximum performance. Concrete successfully smooths out the difference between night and day temperature changes.
When conducting construction works constitute 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.
Rules for the location of vapor barrier layers
To ensure the best performance of multi-layer structures of structures, the rule applies: from the side with more high temperature, have materials with increased resistance to steam penetration with increased thermal conductivity. The layers located outside must have a high vapor conductivity. For normal functioning The enclosing structure requires that the coefficient of the outer layer is five times higher than the coefficient of the layer located inside. 
When this rule is followed, water vapor that has fallen into warm layer walls, it will not be difficult to get out with acceleration 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 layer thickness insulation materials. The quality of the insulation of the entire structure depends on the correctness of the results obtained.
Sergey Novozhilov - expert in roofing materials with 9 years of experience practical work in the field of engineering solutions in construction.
To begin with, 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 excretory system of the body. The sweat emitted by them, evaporating from the surface of the skin, takes with it part 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 provoke 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 mostly cool weather, a person constantly had 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" an excess amount of heat. Thus, the "breathable" material from which clothing is made helps the human body maintain optimal body temperature, preventing overheating or hypothermia.
The "breathing" 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- this is the ability of the material to pass or retain water vapor. In the outdoor clothing and equipment industry importance It has high ability material to water vapor transport. The higher it is, the better, because. this allows the user to avoid overheating and still stay dry.
All fabrics and insulation used today have a certain vapor permeability. However, in numerical terms, it is presented only to describe the properties of membranes used in the manufacture of clothing, and for a very small amount 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 square meter material per day.
This parameter is denoted by the abbreviation MVTR ("moisture vapor transmission rate" or "water vapor transmission rate").
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 methods. Due to the large number of variables that affect the operation of the membrane - individual metabolism, air pressure and humidity, the area of \u200b\u200bthe 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 ready-made garments use a number of techniques. Each of them individually describes the vapor permeability of a fabric or membrane in a certain range of conditions. The following test methods are most commonly used today:
"Japanese" test with "upright cup" (JIS L 1099 A-1)
The test sample is stretched and hermetically fixed over a cup, inside of which is placed a strong desiccant - calcium chloride (CaCl2). The cup is placed on certain time into a thermohydrostat, which maintains an air temperature of 40 ° C and a humidity of 90%.
Depending on how the weight of the desiccant changes during the control time, the 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 of water. After it is turned over and placed over a cup with a dry desiccant - calcium chloride. After the control time, the desiccant is weighed and the MVTR is calculated.
The B-1 test is the most popular, as it shows the highest numbers among all methods that determine the rate of passage of water vapor. Most often, it is his 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 perceptibly vapor-permeable, at least within the framework of not very intensive loads. Finally, for garments with little movement, a vapor permeability of 5-10,000 g/m²/24h is often sufficient.
The JIS L 1099 B-1 test method quite accurately illustrates the performance of a membrane in ideal conditions(when there is condensation on its surface and moisture is transported to a drier environment with a lower temperature).
Sweat plate test or RET (ISO - 11092)
Unlike tests that determine the rate of transport of water vapor through a membrane, the RET technique examines how the test sample resists passage of water vapor.
A tissue or membrane sample is placed on top of a flat porous metal plate, under which a heating element is connected. The temperature of the plate 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 the temperature of the plate constant, the lower the resistance of the test 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 "breathing" properties of the tested sample of the membrane or other material.
- RET 0-6 - extremely breathable;
RET 6-13 - highly breathable; RET 13-20 - breathable; RET more than 20 - not breathing.
Equipment for conducting the ISO-11092 test. On the right is a camera with a "sweating plate". A computer is required to receive and process the 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 "sweating plate" tests are corrected in accordance with the comments of the testers.
Testing clothes with Gore-Tex on a 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 in the list. For this reason, not all outdoor clothing companies can afford it. At the same time, RET is today the main method for assessing the vapor permeability of Gore-Tex membranes.
The RET technique usually correlates well with B-1 test results. 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 have seen that the process of determining the vapor permeability of materials in various methods has many differences, simulating different conditions work.
In addition, various membrane materials work to different principle. So, for example, porous laminates provide a relatively free passage of water vapor through the microscopic pores in their thickness, and pore-free membranes transport moisture to the front surface like a blotter - using hydrophilic polymer chains in their structure. It is quite natural that one test can imitate the winning conditions for the operation of a non-porous membrane film, for example, when moisture is closely adjacent to its surface, and the other for a microporous one.
Taken together, all this means that there is practically no point in comparing materials 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 the 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 - “blowing”, i.e. how much the material is "windproof".
In contrast to the methods for assessing vapor permeability, relative monotony reigns in this area. To evaluate breathability, the so-called Fraser test is used, which determines how much air will pass through the material during the control time. The airflow rate under test conditions is typically 30 mph, but may vary.
The unit of measurement is the cubic foot of air passing through the material in one minute. Abbreviated CFM (cubic feet per minute).
The higher the value, the higher the breathability ("blowing") of the material. Thus, pore-free membranes demonstrate an absolute "non-permeability" - 0 CFM. Test methods are most often defined by ASTM D737 or ISO 9237, which, however, give identical results.
Exact numbers CFMs are published relatively infrequently by fabric and ready-to-wear manufacturers. Most often, this parameter is used to characterize the windproof properties in descriptions. various materials, developed and used in the production of SoftShell clothing.
Recently, manufacturers have begun to “remember” much more often about breathability. 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 accumulation of condensate under clothing. Thus, the Polartec Neoshell membrane has a slightly higher air permeability than traditional porous membranes (0.5 CFM versus 0.1). As a result, Polartec has achieved significant better work of your material in windy conditions and fast 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 chill, blocking about 99% of the air flow. This is enough to withstand even stormy winds, and therefore Neoshell has found itself even in the production of single-layer assault tents (a vivid 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 middle layers with partial breathability, which can also be used as independent product. They use either brand new insulation - like Polartec Alpha - or use synthetic bulk insulation with a very low degree of fiber migration, which allows the use of less dense "breathable" fabrics. For example, Sivera Gamayun jackets use ClimaShield Apex, Patagonia NanoAir uses FullRange™ insulation, which is produced by the Japanese company Toray under the original name 3DeFX+. The same insulation is used in Mountain Force 12 way stretch ski jackets and trousers and Kjus ski clothing. The relatively high breathability of the fabrics in which these heaters are enclosed allows you to create an insulating layer of clothing that will not interfere with the removal of evaporated moisture from the skin surface, helping the user to avoid both getting wet and overheating.
SoftShell-clothing. Subsequently, other manufacturers created an impressive number of their counterparts, which led to the ubiquity of thin, relatively durable, breathable nylon in clothing and equipment for sports and outdoor activities.
There is a legend about the "breathing wall", and legends about the "healthy breathing of the cinder block, which creates a unique atmosphere in the house." In fact, the vapor permeability of the wall is not large, the amount of steam passing through it is insignificant, and much less than the amount of steam carried by air when it is exchanged in the room.
Vapor permeability is one of the most important parameters used in the calculation of insulation. We can say that the vapor permeability of materials determines the entire design of insulation.
What is vapor permeability
The movement of steam through the wall occurs at a difference in partial pressure on the sides of the wall ( different humidity). In this case, there may not be a difference in atmospheric pressure.
Vapor permeability - the ability of a material to pass steam through itself. According to the domestic classification, it is determined by the vapor permeability coefficient m, mg / (m * h * Pa).
The resistance of a layer of material will depend on its thickness.
It is determined by dividing the thickness by the vapor permeability coefficient. It is measured in (m sq. * hour * Pa) / mg.
For example, the vapor permeability coefficient brickwork taken as 0.11 mg/(m*h*Pa). With a brick wall thickness of 0.36 m, its resistance to steam movement will be 0.36 / 0.11 = 3.3 (m sq. * h * Pa) / mg.
What is the vapor permeability of building materials
Below are the values of the coefficient of vapor permeability for several building materials (according to normative document), which are most widely used, mg/(m*h*Pa).
Bitumen 0.008
Heavy concrete 0.03
Autoclaved aerated concrete 0.12
Expanded clay concrete 0.075 - 0.09
Slag concrete 0.075 - 0.14
Burnt clay (brick) 0.11 - 0.15 (in the form of masonry on cement mortar)
Lime mortar 0.12
Drywall, gypsum 0.075
Cement-sand plaster 0.09
Limestone (depending on density) 0.06 - 0.11
Metals 0
Chipboard 0.12 0.24
Linoleum 0.002
Polyfoam 0.05-0.23
Polyurethane hard, polyurethane foam
0,05
Mineral wool 0.3-0.6
Foam glass 0.02 -0.03
Vermiculite 0.23 - 0.3
Expanded clay 0.21-0.26
Wood across the fibers 0.06
Wood along the fibers 0.32
brickwork from silicate brick on cement mortar 0.11
Data on the vapor permeability of the layers must be taken into account when designing any insulation.
How to design insulation - according to vapor barrier qualities
The basic rule of insulation is that the vapor transparency of the layers should increase outward. Then in the cold season, with a greater probability, there will be no accumulation of water in the layers, when condensation occurs at the dew point.
The basic principle helps to decide in any cases. Even when everything is "turned upside down" - they insulate from the inside, despite the insistent recommendations to make insulation only from the outside.
In order to avoid a catastrophe with wetting the walls, it is enough to remember that the inner layer should most stubbornly resist steam, and based on this, for internal insulation apply extruded polystyrene foam in a thick layer - a material with very low vapor permeability.
Or do not forget to use even more “airy” mineral wool for a very “breathing” aerated concrete from the outside.
Separation of layers with a vapor barrier
Another option for applying the principle of vapor transparency of materials in a multilayer structure is the separation of the most significant layers by a vapor barrier. Or the use of a significant layer, which is an absolute vapor barrier.
For example, - insulation of a brick wall with foam glass. It would seem that this contradicts the above principle, because it is possible to accumulate moisture in a brick?
But this does not happen, due to the fact that the directional movement of steam is completely interrupted (at sub-zero temperatures from the room to the outside). After all, foam glass is a complete vapor barrier or close to it.
Therefore, in this case, the brick will enter an equilibrium state with inner atmosphere at home, and will serve as an accumulator of humidity during its sharp jumps indoors, making the indoor climate more pleasant.
The principle of separation of layers is also used when using mineral wool - a heater that is especially dangerous for moisture accumulation. For example, in a three-layer construction, when mineral wool is inside a wall without ventilation, it is recommended to put a vapor barrier under the wool, and thus leave it in the outside atmosphere.
International classification of vapor barrier qualities of materials
The international classification of materials for vapor barrier properties differs from the domestic one.
According to the international standard ISO/FDIS 10456:2007(E), materials are characterized by a coefficient of resistance to steam movement. This coefficient indicates how many times more the material resists the movement of steam compared to air. Those. for air, the coefficient of resistance to steam movement is 1, and for extruded polystyrene foam it is already 150, i.e. Styrofoam is 150 times less vapor permeable than air.
Also in international standards it is customary to determine the vapor permeability for dry and moist materials. The boundary between the concepts of “dry” and “moistened” is the internal moisture content of the material of 70%.
Below are the values of the coefficient of resistance to steam movement for various materials according to international standards.
Steam resistance factor
First, data are given for dry material, and separated by commas for moist (more than 70% moisture).
Air 1, 1
Bitumen 50,000, 50,000
Plastics, rubber, silicone — >5,000, >5,000
Heavy concrete 130, 80
Medium density concrete 100, 60
Polystyrene concrete 120, 60
Autoclaved aerated concrete 10, 6
Lightweight concrete 15, 10
Fake diamond 150, 120
Expanded clay concrete 6-8, 4
Slag concrete 30, 20
Burnt clay (brick) 16, 10
Lime mortar 20, 10
Drywall, plaster 10, 4
Gypsum plaster 10, 6
Cement-sand plaster 10, 6
Clay, sand, gravel 50, 50
Sandstone 40, 30
Limestone (depending on density) 30-250, 20-200
Ceramic tile?, ?
Metals?
OSB-2 (DIN 52612) 50, 30
OSB-3 (DIN 52612) 107, 64
OSB-4 (DIN 52612) 300, 135
Chipboard 50, 10-20
Linoleum 1000, 800
Substrate for plastic laminate 10 000, 10 000
Substrate for laminate cork 20, 10
Polyfoam 60, 60
EPPS 150, 150
Polyurethane hard, polyurethane foam 50, 50
Mineral wool 1, 1
Foam glass?, ?
Perlite panels 5, 5
Perlite 2, 2
Vermiculite 3, 2
Ecowool 2, 2
Expanded clay 2, 2
Wood across grain 50-200, 20-50
It should be noted that the data on the resistance to the movement of steam here and "there" are very different. For example, foam glass is standardized in our country, and the international standard says that it is an absolute vapor barrier.
Where did the legend of the breathing wall come from?
A lot of companies produce mineral wool. This is the most vapor-permeable insulation. According to international standards, its vapor permeability resistance coefficient (not to be confused with the domestic vapor permeability coefficient) is 1.0. Those. in fact, mineral wool does not differ in this respect from air.
Indeed, it is a "breathing" insulation. In order to sell mineral wool as much as possible, you need beautiful fairy tale. For example, that if you insulate a brick wall from the outside mineral wool, then she will not lose anything in terms of vapor permeability. And this is absolutely true!
The insidious lie is hidden in the fact that through brick walls 36 centimeters thick, with a humidity difference of 20% (outside 50%, in the house - 70%), about a liter of water will come out of the house per day. While with air exchange, about 10 times more should come out so that the humidity in the house does not increase.
And if the wall is insulated from the outside or from the inside, for example with a layer of paint, vinyl wallpaper, dense cement plaster, (which, in general, is “the most common thing”), then the vapor permeability of the wall will decrease several times, and with complete insulation - tens and hundreds of times.
Therefore, always brick wall and households will be absolutely the same whether the house is covered with mineral wool with “raging breath”, or “dull-sniffling” foam plastic.
When making decisions on the insulation of houses and apartments, it is worth proceeding from the basic principle - the outer layer should be more vapor-permeable, preferably at times.
If for some reason it is not possible to withstand this, then it is possible to separate the layers with a continuous vapor barrier (use a completely vapor-tight layer) and stop the movement of steam in the structure, which will lead to a state of dynamic equilibrium of the layers with the environment in which they will be located.
Vapor permeability of walls - get rid of fiction.
In this article, we will try to answer the following FAQ: what is vapor permeability and is vapor barrier needed when building house walls from foam blocks or bricks. Here are just a few typical questions our clients ask:
« Among the many different answers on the forums, I read about the possibility of filling the gap between porous ceramic masonry and facing ceramic bricks with ordinary masonry mortar. Does this not contradict the rule of reducing the vapor permeability of the layers from the inner to the outer, because the vapor permeability cement-sand mortar more than 1.5 times lower than ceramics? »
Or here's another: Hello. There is a house made of aerated concrete blocks, I would like, if not to veneer the whole house, then at least decorate the house with clinker tiles, but some sources write that it is impossible directly on the wall - it must breathe, what to do ??? And then some give a diagram of what is possible ... Question: How is ceramic facade clinker tile attached to foam blocks ?»
For correct answers to such questions, we need to understand the concepts of "vapor permeability" and "resistance to vapor transfer".
So, the vapor permeability of a layer of material is the ability to pass or retain water vapor as a result of the difference in the partial pressure of water vapor at the same atmospheric pressure on both sides of the layer of material, characterized by the value of the coefficient of vapor permeability or permeability resistance when exposed to water vapor. unit of measurementµ - design coefficient of vapor permeability of the material of the layer of the building envelope mg / (m h Pa). The coefficients for various materials can be found in the table in SNIP II-3-79.
The coefficient of resistance to diffusion of water vapor is a dimensionless value showing how many times fresh air more permeable to vapor than any other material. Diffusion resistance is defined as the product of the diffusion coefficient of a material and its thickness in meters and has a dimension in meters. The resistance to vapor permeability of a multilayer building envelope is determined by the sum of the resistances to vapor permeability of its constituent layers. But in paragraph 6.4. SNIP II-3-79 states: “It is not required to determine the vapor permeability resistance of the following enclosing structures: a) homogeneous (single-layer) external walls of rooms with dry or normal conditions; b) two-layer outer walls of rooms with dry or normal conditions, if the inner layer of the wall has a vapor permeability of more than 1.6 m2 h Pa / mg. In addition, in the same SNIP it says:
"Resistance to vapor permeability air gaps in enclosing structures should be taken equal to zero, regardless of the location and thickness of these layers.
So what happens in the case of multilayer structures? To prevent the accumulation of moisture in a multilayer wall when steam moves from inside the room to the outside, each subsequent layer must have a greater absolute vapor permeability than the previous one. It is absolute, i.e. total, calculated taking into account the thickness of a certain layer. Therefore, it is impossible to say unequivocally that aerated concrete cannot, for example, be lined with clinker tiles. In this case, the thickness of each layer matters. wall structure. The greater the thickness, the lower the absolute vapor permeability. The higher the value of the product µ * d, the less vapor permeable the corresponding layer of material. In other words, to ensure the vapor permeability of the wall structure, the product µ * d must increase from the outer (outer) layers of the wall to the inner ones.
For example, cover gas silicate blocks 200 mm thick clinker tiles 14 mm thick cannot be used. With this ratio of materials and their thicknesses, the ability to pass vapors from finishing material will be 70% less than blocks. If the thickness bearing wall will be 400 mm, and the tiles are still 14 mm, then the situation will be the opposite and the ability to pass pairs of tiles will be 15% more than that of blocks.
For a competent assessment of the correctness of the wall structure, you will need the values of the diffusion resistance coefficients µ, which are presented in the following table:
Material name | Density, kg/m3 | Thermal conductivity, W/m*K | Diffusion resistance coefficient |
Clinker brick solid | 2000 | 1,05 | |
Hollow clinker brick (with vertical voids) | 1800 | 0,79 | |
Solid, hollow and porous ceramic bricks and blocks gas silicate. | 0,18 | ||
0,38 | |||
0,41 | |||
1000 | 0,47 | ||
1200 | 0,52 |
If for facade decoration ceramic tiles are used, then there will be no problem with vapor permeability for any reasonable combination of the thicknesses of each layer of the wall. The diffusion resistance coefficient µ for ceramic tiles will be in the range of 9-12, which is an order of magnitude less than that of clinker tiles. For a problem with the vapor permeability of a lined wall ceramic tiles 20 mm thick, the thickness of the bearing wall made of gas silicate blocks with a density of D500 should be less than 60 mm, which contradicts SNiP 3.03.01-87 "Bearing and enclosing structures" clause 7.11, table No. 28, which establishes a minimum thickness of the bearing wall of 250 mm.
The issue of filling gaps between different layers of masonry materials is solved in a similar way. To do this, it is enough to consider this wall structure in order to determine the vapor transfer resistance of each layer, including the filled gap. Indeed, in a multilayer wall structure, each subsequent layer in the direction from the room to the street should be more vapor permeable than the previous one. Calculate the water vapor diffusion resistance value for each layer of the wall. This value is determined by the formula: the product of the layer thickness d and the diffusion resistance coefficient µ. For example, the 1st layer - ceramic block. For it, we choose the value of the diffusion resistance coefficient 5, using the table above. The product d x µ \u003d 0.38 x 5 \u003d 1.9. 2nd layer - normal masonry mortar- has a diffusion resistance coefficient µ = 100. The product d x µ =0.01 x 100 = 1. Thus, the second layer - an ordinary masonry mortar - has a diffusion resistance value less than the first one, and is not a vapor barrier.
Given the above, let's look at the proposed wall design options:
1. Load-bearing wall in KERAKAM Superthermo with FELDHAUS KLINKER hollow brick cladding.
To simplify the calculations, we assume that the product of the diffusion resistance coefficient µ and the thickness of the material layer d is equal to the value M. Then, M superthermo = 0.38 * 6 = 2.28 meters, and M clinker (hollow, NF format) = 0.115 * 70 = 8.05 meters. Therefore, when applying clinker brick ventilation gap required:
