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Vapor permeability of walls - we get rid of fiction.

In this article we will try to answer the following FAQ: what is vapor permeability and is vapor barrier necessary when building walls of a house made of foam blocks or bricks. Here are just a few typical questions our clients ask:

« Among many different answers on the forums, I read about the possibility of filling the gap between porous ceramic masonry and facing ceramic bricks ordinary masonry mortar. Doesn’t this contradict the rule of reducing the vapor permeability of layers from internal to external, because vapor permeability cement-sand mortar more than 1.5 times lower than ceramics? »

Or here’s another: “ Hello. I have a house made of aerated concrete blocks, I would like, if not to tile the whole thing, then at least to decorate the house with clinker tiles, but some sources write that you can’t put it directly on the wall - it has to breathe, what should I do??? And then some give a diagram of what is possible... Question: How are ceramic facade clinker tiles attached to foam blocks ?»

To correctly answer such questions, we need to understand the concepts of “vapor permeability” and “resistance to vapor transfer”.

So, the vapor permeability of a material layer is the ability to transmit 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 material layer, characterized by the value of the vapor permeability coefficient or permeability resistance when exposed to water vapor. Unitµ - calculated coefficient of vapor permeability of the material of the layer of the enclosing structure mg / (m hour Pa). Odds for various materials can be viewed in the table in SNIP II-3-79.

The coefficient of resistance to water vapor diffusion is a dimensionless quantity that shows 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 vapor permeability resistance of a multilayer enclosing structure is determined by the sum of the vapor permeability resistances 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 external walls of rooms with dry or normal conditions, if inner layer the wall has a vapor permeation resistance of more than 1.6 m2 h Pa/mg.” In addition, the same SNIP says:

"Resistance to vapor permeation 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 moisture accumulation in multilayer wall when steam moves from inside the room to the outside, each subsequent layer must have greater absolute vapor permeability than the previous one. Precisely 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 faced with clinker tiles. In this case, the thickness of each layer of the wall structure is important. 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 is. In other words, to ensure 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, veneer 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 transmit vapors of the finishing material will be 70% less than that of the blocks. If the thickness load-bearing wall will be 400 mm, and the tiles are still 14 mm, then the situation will be the opposite and the ability of the tiles to pass vapors will be 15% greater than that of the blocks.

To correctly assess the correctness of the wall structure, you will need the values ​​of the diffusion resistance coefficients µ, which are presented in the table below:

If for facade finishing ceramic tiles are used, then there will be no problem with vapor permeability with any reasonable combination of thicknesses of each layer of the wall. The diffusion resistance coefficient µ of ceramic tiles will be in the range of 9-12, which is an order of magnitude less than that of clinker tiles. For problems with vapor permeability of a lined wall ceramic tiles 20 mm thick, the thickness of the load-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 "Load-bearing and enclosing structures" clause 7.11 table No. 28, which establishes minimum thickness load-bearing wall 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 design walls to determine the vapor transfer resistance of each layer, including the filled gap. Indeed, in a multi-layer wall structure, each subsequent layer in the direction from the room to the street should be more vapor permeable than the previous one. Let's calculate the value of resistance to water vapor diffusion 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, 1st layer - ceramic block. For it we select the value of the diffusion resistance coefficient 5, using the table above. Product d x µ = 0.38 x 5 = 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 - ordinary masonry mortar - has a diffusion resistance value less than the first, and is not a vapor barrier.

Considering the above, let's look at the proposed wall design options:

1. Load-bearing wall made of KERAKAM Superthermo clad with FELDHAUS KLINKER hollow clinker bricks.

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 using clinker bricks, a ventilation gap is necessary:

During the construction process, any material must first of all be assessed according to its operational and technical characteristics. When solving the problem of building a “breathing” house, which is most typical of buildings made of brick or wood, or vice versa, achieving maximum resistance to vapor permeability, you need to know and be able to operate tabular constants to obtain calculated vapor permeability indicators building materials.

What is vapor permeability of materials

Vapor permeability of materials- the ability to transmit or retain water vapor as a result of the difference in the partial pressure of water vapor on both sides of the material at the same atmospheric pressure. Vapor permeability is characterized by a vapor permeability coefficient or vapor permeability resistance and is standardized by SNiP II-3-79 (1998) " Construction heating engineering", namely Chapter 6 "Resistance to vapor permeation of enclosing structures"

Table of vapor permeability of building materials

The vapor permeability table is presented in SNiP II-3-79 (1998) “Building Heat Engineering”, Appendix 3 “Thermal Indicators of Construction Materials”. The vapor permeability and thermal conductivity indicators of the most common materials used for construction and insulation of buildings are presented in the table below.

Table of vapor permeability of building materials

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.

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 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.

Vapor permeability means Latin letterμ 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 a difference in external and internal pressure of 1 Pa.

High ability to conduct water vapor in:

• foam concrete;
• aerated concrete;
• perlite concrete;
• expanded clay concrete.

Rounding out the table is heavy concrete.

Advice: if you need to make a technological channel in the foundation, diamond drilling of holes in concrete will help you.

Aerated concrete

1. 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.
2. Any aerated concrete and foam concrete block contains ≈ 60% air, due to which the vapor permeability of aerated concrete is recognized to be at a good level, the walls in this case can “breathe”.
3. Water vapor seeps freely 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 it is 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, you should consider this feature and select appropriate plasters, putties and paints.

The instructions strictly regulate that their vapor permeability parameters are not lower than aerated concrete blocks used for construction.

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 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 aerated concrete D400, 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. Please also note that if you have used it for exterior finishing vapor-permeable paint for aerated concrete, and for the interior - non-vapor-permeable materials, 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 can’t cut the expanded clay block with a regular circle and grinder, use a diamond one.
For example, cutting reinforced concrete diamond wheels 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 yourself.

Today more attention begins to pay attention not only to the thermal properties of wall structures, but also to the comfort of living in the structure. 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. The vapor permeability of foam concrete and aerated concrete, as well as heavy concrete, differs in its characteristics, which must be taken into account when choosing finishing materials. The video in this article will help you find additional information on this topic.

There is a legend about a “breathing wall”, and tales about the “healthy breathing of a 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 calculating insulation. We can say that the vapor permeability of materials determines the entire insulation design.

What is vapor permeability

The movement of steam through the wall occurs when there is a difference in partial pressure on the sides of the wall (different humidity). At the same time, the differences atmospheric pressure there may not be.

Vapor permeability is 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*hour*Pa).

The resistance of a layer of material will depend on its thickness.
Determined by dividing the thickness by the vapor permeability coefficient. Measured in (m sq.*hour*Pa)/mg.

For example, the vapor permeability coefficient brickwork accepted as 0.11 mg/(m*hour*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.*hour*Pa)/mg.

What is the vapor permeability of building materials?

Below are the values ​​of the vapor permeability coefficient for several building materials (according to normative document), which are most widely used, mg/(m*hour*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
Foam plastic 0.05-0.23
Polyurethane solid, 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 grain 0.06
Wood along the grain 0.32
Brickwork made of sand-lime brick on cement mortar 0.11

Data on the vapor permeability of layers must be taken into account when designing any insulation.

How to design insulation - based on vapor barrier qualities

The basic rule of insulation is that the vapor transparency of layers should increase towards the outside. Then, during the cold season, it is more likely that water will not accumulate in the layers when condensation occurs at the dew point.

The basic principle helps to make a decision in any case. Even when everything is “turned upside down,” they insulate from the inside, despite persistent recommendations to do insulation only from the outside.

To avoid a catastrophe with the walls getting wet, 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 don’t forget to use even more “airy” mineral wool on the outside for very “breathable” aerated concrete.

Separation of layers with a vapor barrier

Another option for applying the principle of vapor transparency of materials in a multilayer structure is to separate the most significant layers with a vapor barrier. Or the use of a significant layer, which is an absolute vapor barrier.

For example, insulating a brick wall with foam glass. It would seem that this contradicts the above principle, since it is possible for moisture to accumulate in the 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 into a state of equilibrium with the internal atmosphere of the house, and will serve as an accumulator of humidity during sudden changes indoors, making the internal climate more pleasant.

The principle of layer separation is also used when using mineral wool - an insulation material that is especially dangerous due to moisture accumulation. For example, in a three-layer construction, when mineral wool is located inside a wall without ventilation, it is recommended to place 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 based on 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 vapor 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. Expanded polystyrene is 150 times less permeable to steam than air.

It is also customary in international standards to determine vapor permeability for dry and moistened materials. The internal humidity of the material is 70% as the boundary between the concepts of “dry” and “moistened”.
Below are the steam resistance coefficient values ​​for various materials according to international standards.

Steam resistance coefficient

Data are given first for dry material, and separated by commas for moistened material (more than 70% humidity).
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
Fired clay (brick) 16, 10
Lime mortar 20, 10
Drywall, gypsum 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
Underlay for plastic laminate 10,000, 10,000
Underlay for laminate cork 20, 10
Foam plastic 60, 60
EPPS 150, 150
Solid polyurethane, 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 the grain 50-200, 20-50

It should be noted that the data on resistance to steam movement 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 is no different in this respect from air.

Indeed, this is a “breathable” insulation. To sell as much mineral wool as possible, you need a beautiful fairy tale. For example, if you insulate a brick wall from the outside mineral wool, then it will not lose anything in terms of vapor permeability. And this is the absolute truth!

The insidious lie is hidden in the fact that through brick walls 36 centimeters thick, with a humidity difference of 20% (on the street 50%, in the house - 70%) about a liter of water will leave the house per day. While with the exchange of air, 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 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 by several times, and with complete insulation - by tens and hundreds of times.

Therefore always brick wall and it will be absolutely the same for household members whether the house is covered with mineral wool with “raging breath”, or with “sadly sniffling” polystyrene foam.

When making decisions on insulating houses and apartments, it is worth proceeding from the basic principle - the outer layer should be more vapor permeable, preferably by several times.

If for some reason it is not possible to withstand this, then you can separate the layers with a continuous vapor barrier (use a completely vapor-proof 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.

The vapor permeability table of materials is building code domestic and, of course, international standards. In general, vapor permeability is a certain ability of fabric layers to actively transmit water vapor due to different pressure results with a uniform atmospheric indicator on both sides of the element.

The ability to transmit and retain water vapor under consideration is characterized by special values ​​called the coefficient of resistance and vapor permeability.

At this point, it is better to focus your attention on the internationally established ISO standards. They determine the high-quality vapor permeability of dry and wet elements.

A large number of people are committed to the idea that breathing is good sign. However, it is not. Breathable elements are those structures that allow both air and vapor to pass through. Expanded clay, foam concrete and trees have increased vapor permeability. In some cases, bricks also have these indicators.

If a wall is endowed with high vapor permeability, this does not mean that breathing becomes easy. Indoors recruited a large number of moisture, accordingly, low resistance to frost appears. Coming out through the walls, the vapor turns into ordinary water.

Most manufacturers do not take into account when calculating this indicator important factors, that is, they are being cunning. According to them, each material is thoroughly dried. Damp ones increase thermal conductivity five times, therefore, it will be quite cold in an apartment or other room.

The most terrible moment is the drop in night temperature conditions, leading to a shift in the dew point in the wall openings and further freezing of the condensate. Subsequently, the resulting frozen water begins to actively destroy surfaces.

Indicators

The table indicates the vapor permeability of materials:

1. , which is an energetic type of heat transfer from highly heated particles to less heated ones. Thus, equilibrium is achieved and appears in temperature conditions. With high indoor thermal conductivity, you can live as comfortably as possible;
2. Thermal capacity calculates the amount of heat supplied and contained. Him in mandatory must be brought to a real volume. This is how temperature change is considered;
3. Thermal absorption is the enclosing structural alignment in temperature fluctuations, that is, the degree of absorption of moisture by wall surfaces;
4. Thermal stability is a property that protects structures from sharp thermal oscillatory flows. Absolutely all full comfort in a room depends on the general thermal conditions. Thermal stability and capacity can be active in cases where the layers are made of materials with increased thermal absorption. Stability ensures the normalized state of structures.

Vapor permeability mechanisms

At low levels of relative humidity, moisture in the atmosphere is actively transported through existing pores in building components. They acquire appearance, similar to individual molecules of water vapor.

In cases where humidity begins to rise, the pores in the materials are filled with liquids, directing the working mechanisms to be downloaded into capillary suction. Vapor permeability begins to increase, lowering the resistance coefficients, as the humidity in the building material increases.

For internal structures in already heated buildings, dry-type vapor permeability indicators are used. In places where the heating is variable or temporary, wet types of building materials are used, intended for external construction.

Vapor permeability of materials, the table helps to effectively compare various types of vapor permeability.

Equipment

In order to correctly determine vapor permeability indicators, specialists use specialized research equipment:

1. Glass cups or vessels for research;
2. Unique tools required for thickness measuring processes with high level accuracy;
3. Analytical type balances with weighing error.