Air permeability of building materials. Vapor permeability of building materials

In domestic standards, the vapor permeability resistance ( vapor permeability Rp, m2. h Pa/mg) is standardized in chapter 6 "Resistance to vapor permeability of enclosing structures" SNiP II-3-79 (1998) "Construction heat engineering".

International standards for the vapor permeability of building materials are given in ISO TC 163/SC 2 and ISO/FDIS 10456:2007(E) - 2007.

The vapor permeability coefficient indicators are determined on the basis of the international standard ISO 12572 "Thermal properties of building materials and products - Determination of vapor permeability". Vapor permeability indicators for international ISO standards were determined in a laboratory method on time-tested (not just released) samples of building materials. Vapor permeability was determined for building materials in a dry and wet state.
In the domestic SNiP, only calculated data on vapor permeability are given at a mass ratio of moisture in the material w,%, equal to zero.
Therefore, for the choice of building materials for vapor permeability in summer cottage construction it is better to focus on international ISO standards, which determine the vapor permeability of "dry" building materials at a moisture content of less than 70% and "wet" building materials at a moisture content of more than 70%. Remember that when leaving the "pies" of vapor-permeable walls, the vapor permeability of materials from the inside to the outside should not decrease, otherwise the inner layers of building materials will gradually "freeze" and their thermal conductivity will increase significantly.

The vapor permeability of materials from the inside to the outside of the heated house should decrease: SP 23-101-2004 Design of thermal protection of buildings, clause 8.8: To ensure better performance in multilayer building structures, on the warm side, layers of greater thermal conductivity and greater resistance to vapor permeation should be placed than the outer layers. According to T. Rogers (Rogers T.S. Designing thermal protection of buildings. / Lane from English - m.: si, 1966) Separate layers in multilayer fences should be arranged in such a sequence that the vapor permeability of each layer increases from the inner surface to outdoor. With such an arrangement of layers, water vapor that has entered the enclosure through the inner surface with increasing ease will pass through all the barriers of the enclosure and be removed from the enclosure from the outer surface. The enclosing structure will function normally if, subject to the formulated principle, the vapor permeability of the outer layer is at least 5 times higher than the vapor permeability of the inner layer.

Mechanism of vapor permeability of building materials:

At low relative humidity, moisture from the atmosphere is in the form of individual water vapor molecules. With an increase in relative humidity, the pores of building materials begin to fill with liquid and the mechanisms of wetting and capillary suction begin to work. With an increase in the humidity of the building material, its vapor permeability increases (the vapor permeability resistance coefficient decreases).

ISO/FDIS 10456:2007(E) vapor permeability ratings for "dry" building materials apply to internal structures of heated buildings. Vapor permeability indicators of "wet" building materials are applicable to all external structures and internal structures of unheated buildings or country houses with a variable (temporary) heating regime.

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 with 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 of brickwork is 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 the regulatory 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 bricks 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, use extruded polystyrene foam with 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 into an equilibrium state with the internal atmosphere of the house, and will serve as an accumulator of humidity during its sharp jumps inside the room, making the internal 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 coefficient

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
Artificial stone 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. To sell mineral wool as much as possible, you need a beautiful fairy tale. For example, that if you insulate a brick wall from the outside with mineral wool, then it will not lose anything in terms of vapor permeability. And this is absolutely true!

An 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 leave 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, it will always be absolutely the same for a brick wall and for households - whether the house is covered with mineral wool with “raging breath”, or “dull-sniffing” polystyrene.

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.

2. Unfortunately, we lose the storage heat capacity of the outer wall array forever. But there is a win here:

A) there is no need to spend energy on heating these walls

B) when you turn on even the smallest heater in the room, it will almost immediately become warm.

3. At the junction of the wall and the ceiling, "cold bridges" can be removed if the insulation is applied partially on the floor slabs with subsequent decoration of these junctions.

4. If you still believe in the "breathing of the walls", then please read THIS article. If not, then there is an obvious conclusion: the heat-insulating material must be pressed very tightly against the wall. It is even better if the insulation becomes one with the wall. Those. there will be no gaps and cracks between the insulation and the wall. Thus, the moisture from the room will not be able to get into the dew point zone. The wall will always remain dry. Seasonal temperature fluctuations without moisture access will not adversely affect the walls, which will increase their durability.

All these tasks can be solved only by sprayed polyurethane foam.

Possessing the lowest coefficient of thermal conductivity of all existing thermal insulation materials, polyurethane foam will take up a minimum of internal space.

The ability of polyurethane foam to adhere reliably to any surface makes it easy to apply it to the ceiling to reduce "cold bridges".

When applied to walls, polyurethane foam, being in a liquid state for some time, fills all the cracks and microcavities. Foaming and polymerizing directly at the point of application, polyurethane foam becomes one with the wall, blocking access to destructive moisture.

VAPOR PERMEABILITY OF WALLS
Supporters of the false concept of “healthy breathing of the walls”, in addition to sinning against the truth of physical laws and deliberately misleading designers, builders and consumers, based on a mercantile urge to sell their goods by any means, slander and slander thermal insulation materials with low vapor permeability (polyurethane foam) or heat-insulating material and completely vapor-tight (foam glass).

The essence of this malicious insinuation boils down to the following. It seems like if there is no notorious “healthy breathing of the walls”, then in this case the interior will definitely become damp, and the walls will ooze moisture. In order to debunk this fiction, let's take a closer look at the physical processes that will occur in the case of lining under the plaster layer or using inside the masonry, for example, a material such as foam glass, the vapor permeability of which is zero.

So, due to the heat-insulating and sealing properties inherent in foam glass, the outer layer of plaster or masonry will come into an equilibrium temperature and humidity state with the outside atmosphere. Also, the inner layer of masonry will enter into a certain balance with the microclimate of the interior. Water diffusion processes, both in the outer layer of the wall and in the inner one; will have the character of a harmonic function. This function will be determined, for the outer layer, by diurnal changes in temperature and humidity, as well as seasonal changes.

Particularly interesting in this respect is the behavior of the inner layer of the wall. In fact, the inside of the wall will act as an inertial buffer, the role of which is to smooth out sudden changes in humidity in the room. In the event of a sharp humidification of the room, the inner part of the wall will adsorb the excess moisture contained in the air, preventing the air humidity from reaching the limit value. At the same time, in the absence of moisture release into the air in the room, the inner part of the wall begins to dry out, preventing the air from “drying out” and becoming like a desert one.

As a favorable result of such an insulation system using polyurethane foam, the harmonics of fluctuations in air humidity in the room are smoothed out and thus guarantee a stable value (with minor fluctuations) of humidity acceptable for a healthy microclimate. The physics of this process has been studied quite well by the developed construction and architectural schools of the world, and in order to achieve a similar effect when using fiber inorganic materials as a heater in closed insulation systems, it is highly recommended to have a reliable vapor-permeable layer on the inside of the insulation system. So much for "healthy breathing walls"!

Building materials for the most part are porous bodies. The size and structure of the pores in different materials is not the same, therefore, the air permeability of materials, depending on the pressure difference, manifests itself in different ways.

Figure 11 shows a qualitative picture of the dependence of air permeability G from pressure difference ΔР for building materials, given by K.F. Fokin.

Fig.11. Effect of material porosity on its air permeability.1 - materials with uniform porosity (such as foam concrete); 2 - materials with pores of various sizes (such as fillings); 3 - low air-permeable materials (such as wood, cement mortars), 4 - wet materials.

Straight line from 0 to point a on curve 1 indicates the laminar movement of air through the pores of the material with uniform porosity at small values ​​of the pressure difference. Above this point, turbulent motion occurs on the curved section. In materials with different pore sizes, the air movement is turbulent even at a small pressure difference, which can be seen from the curvature of line 2. In materials with low air permeability, on the contrary, the air movement through the pores is laminar and at fairly large pressure differences, therefore, the dependence G from ΔР linear for any pressure difference (line 3). In wet materials (curve 4) at low ΔР, less than a certain minimum pressure difference ΔP min, there is no air permeability, and only when this value is exceeded, when the pressure difference is sufficient to overcome the forces of surface tension of the water contained in the pores of the material, air movement occurs. The higher the moisture content of the material, the greater the value ΔP min.

With laminar air movement in the pores of the material, the dependence is valid

where G is the air permeability of the fence or layer of material, kg / (m 2. h);

i- air permeability coefficient of the material, kg / (m. Pa. h);

δ - thickness of the material layer, m.

Air permeability coefficient of the material similar to the coefficient of thermal conductivity and indicates the degree of air permeability of the material, numerically equal to the air flow in kg passing through 1 m 2 of an area perpendicular to the direction of flow, at a pressure gradient of 1 Pa / m.

The values ​​of the air permeability coefficient for various building materials differ significantly from each other.

For example, for mineral wool i ≈ 0.044 kg / (m. Pa. h), for non-autoclaved foam concrete i ≈ 5.3.10 - 4 kg / (m. Pa. h), for solid concrete i ≈ 5.1.10 - 6 kg / (m. Pa. h),

With turbulent air movement in formula (2.60) should be replaced ΔР on the ΔР n. At the same time, the exponent n varies within 0.5 - 1. However, in practice, formula (2.60) is also used for the turbulent regime of air flow in the pores of the material.

In modern regulatory literature, the concept of air permeability coefficient is not used. Materials and designs are characterized air permeability R and, kg / (m. h). at a pressure difference on different sides ∆Р o = 10 Pa, which, with laminar air movement, is found by the formula:

where G is the breathability of a layer of material or structure, kg / (m 2. h).

The resistance to air penetration of fences in its dimension does not contain the dimension of air transfer potential - pressure. This situation arose due to the fact that in regulatory documents, by dividing the actual pressure difference ∆P by the standard pressure value ∆P o =10 Pa, the air permeability resistance is reduced to a pressure difference ∆P o = 10 Pa.

The values ​​are given breathability for layers of some materials and structures.

For windows, in the leaks of which the movement of air occurs in mixed mode, the resistance to air penetration , kg / (m. h), is determined from the expression:

Questions for self-control

1. What is the breathability of the material and fence?

2. What is breathability?

3. What is infiltration?

4. What is exfiltration?

5. What quantitative characteristic of the process of air permeability is called air permeability?

6. Through what two types of leaks is air filtered in fences?

7. What are the three types of filtration, according to the terminology of R.E. Brilinga?

8. What is the breathability potential?

9. What two natures form the pressure difference on opposite sides of the fence?

10. What is the air permeability coefficient of the material?

11. What is the air permeability of the building envelope?

12. Write a formula for determining the resistance to air penetration during laminar movement of air through the pores of construction materials.

13. Write a formula for determining the window's air permeability.

For the most part, they are porous bodies. The size and structure of the pores in different materials is not the same, therefore, the air permeability of materials, depending on the pressure difference, manifests itself in different ways.

Figure 11 shows a qualitative picture of the dependence of air permeability G from pressure difference ΔР for building materials, given by K.F. Fokin.

Fig.11. Effect of material porosity on its air permeability.1 - materials with uniform porosity (such as foam concrete); 2 - materials with pores of various sizes (such as fillings); 3 - low air-permeable materials (such as wood, cement mortars), 4 - wet materials.

Straight line from 0 to point a on curve 1 indicates the laminar movement of air through the pores of the material with uniform porosity at small values ​​of the pressure difference. Above this point, turbulent motion occurs on the curved section. In materials with different pore sizes, the air movement is turbulent even at a small pressure difference, which can be seen from the curvature of line 2. In materials with low air permeability, on the contrary, the air movement through the pores is laminar and at fairly large pressure differences, therefore, the dependence G from ΔР linear for any pressure difference (line 3). In wet materials (curve 4) at low ΔР, less than a certain minimum pressure difference ΔP min, there is no air permeability, and only when this value is exceeded, when the pressure difference is sufficient to overcome the forces of surface tension of the water contained in the pores of the material, air movement occurs. The higher the moisture content of the material, the greater the value ΔP min.

With laminar air movement in the pores of the material, the dependence is valid

where G is the air permeability of the fence or layer of material, kg / (m 2. h);

i- air permeability coefficient of the material, kg / (m. Pa. h);

δ - thickness of the material layer, m.

Air permeability coefficient of the material similar to the coefficient of thermal conductivity and indicates the degree of air permeability of the material, numerically equal to the air flow in kg passing through 1 m 2 of an area perpendicular to the direction of flow, at a pressure gradient of 1 Pa / m.

The values ​​of the air permeability coefficient for various building materials differ significantly from each other.

For example, for mineral wool i ≈ 0.044 kg / (m. Pa. h), for non-autoclaved foam concrete i ≈ 5.3.10 - 4 kg / (m. Pa. h), for solid concrete i ≈ 5.1.10 - 6 kg / (m. Pa. h),

With turbulent air movement in formula (2.60) should be replaced ΔР on the ΔР n. At the same time, the exponent n varies within 0.5 - 1. However, in practice, formula (2.60) is also used for the turbulent regime of air flow in the pores of the material.

In modern regulatory literature, the concept of air permeability coefficient is not used. Materials and designs are characterized air permeability R and, kg / (m. h). with a pressure difference on different sides? P o \u003d 10 Pa, which, with laminar air movement, is found by the formula:

where G is the breathability of a layer of material or structure, kg / (m 2. h).

The resistance to air penetration of fences in its dimension does not contain the dimension of air transfer potential - pressure. This situation arose due to the fact that in regulatory documents, by dividing the actual pressure difference? P by the standard pressure value? P o \u003d 10 Pa, the air permeability resistance is reduced to a pressure difference? P o \u003d 10 Pa.

The values ​​are given breathability for layers of some materials and structures.

For windows, in the leaks of which the movement of air occurs in mixed mode, the resistance to air penetration , kg / (m. h), is determined from the expression:

Questions for self-control

1. What is the breathability of the material and fence?

2. What is breathability?

3. What is infiltration?

4. What is exfiltration?

5. What quantitative characteristic of the process of air permeability is called air permeability?

6. Through what two types of leaks is air filtered in fences?

7. What are the three types of filtration, according to the terminology of R.E. Brilinga?

8. What is the breathability potential?

9. What two natures form the pressure difference on opposite sides of the fence?

10. What is the air permeability coefficient of the material?

11. What is the air permeability of the building envelope?

12. Write a formula for determining the resistance to air penetration during laminar movement of air through the pores of construction materials.

13. Write a formula for determining the window's air permeability.