Air permeability coefficient of building materials table. Air permeability of building materials. How to design insulation - according to vapor barrier qualities

Building materials for the most part are porous bodies. Size and structure of pores various 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 various sizes(type of filling); 3 - low breathable 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 from different sizes pores, the air movement is turbulent even at a small pressure difference, which is evident from the curvature of line 2. In low-air-permeable materials, 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 is 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). h),

With turbulent air movement in formula (2.60) should be replaced ΔР on 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.

During the construction process, any material should first of all be evaluated according to its operational and technical characteristics. When solving the problem of building a “breathing” house, which is most characteristic of buildings made of brick or wood, or vice versa, to achieve maximum resistance to vapor permeability, it is necessary to know and be able to operate with tabular constants to obtain calculated indicators of vapor permeability of building materials.

What is the vapor permeability of materials

- the ability to pass 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 normalized by SNiP II-3-79 (1998) "Construction heating engineering", namely chapter 6 "Vapor permeability resistance of enclosing structures"

The vapor permeability table is presented in SNiP II-3-79 (1998) "Construction heat engineering", Appendix 3 "Thermal performance of building materials for structures". The vapor permeability and thermal conductivity of the most common materials used for the construction and insulation of buildings are presented in the table below.

Material	Density, kg/m3	Thermal conductivity, W / (m * C)	Vapor permeability, Mg/(m*h*Pa)
Aluminum
asphalt concrete
Drywall
Chipboard, OSB
Oak along the grain
Oak across the grain
Reinforced concrete
Facing cardboard
Expanded clay
Expanded clay
Expanded clay concrete
Expanded clay concrete
Brick ceramic hollow (gross 1000)
Brick ceramic hollow (gross 1400)
Red clay brick
Brick, silicate
Linoleum
mineral wool
mineral wool
foam concrete
foam concrete
PVC foam
Styrofoam
Styrofoam
Styrofoam
EXTRUDED POLYSTYRENE FOAM
POLYURETHANE FOAM
POLYURETHANE FOAM
POLYURETHANE FOAM
POLYURETHANE FOAM
Foam glass
Foam glass
Sand
POLYUREA
POLYURETHANE MASTIC
Polyethylene
Ruberoid, glassine
Pine, spruce along the grain
Pine, spruce across the grain
Plywood

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 resistance 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, layers of higher thermal conductivity and greater resistance to vapor permeation should be placed on the warm side 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 this arrangement of layers, water vapor that has entered the fence through inner surface with increasing ease, will pass through all the guardrails and be removed from the outer surface of the guardrail. 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. The vapor permeability values ​​of "wet" building materials are applicable to all external structures and internal structures of unheated buildings or country houses with variable (temporary) heating mode.

Figure 1 - vapor permeability of a galvanized flashing

According to SP 50.13330.2012 "Thermal protection of buildings", Appendix T, table T1 "Designed thermal performance of building materials and products", the vapor permeability coefficient of a galvanized flashing (mu, (mg / (m * h * Pa)) will be equal to:

Conclusion: the internal galvanized flashing (see Figure 1) in translucent structures can be installed without a vapor barrier.

For the installation of a vapor barrier circuit, it is recommended:

Vapor barrier of the fastening points of the galvanized sheet, this can be provided with mastic

Vapor barrier of joints of galvanized sheet

Vapor barrier of elements joining points (galvanized sheet and stained-glass crossbar or rack)

Ensure that there is no steam transmission through fasteners (hollow rivets)

Terms and Definitions

Vapor permeability- the ability of materials to pass water vapor through their thickness.

Water vapor is the gaseous state of water.

The dew point characterizes the amount of humidity in the air (water vapor content in the air). The dew point temperature is defined as the ambient temperature to which the air must be cooled in order for the vapor it contains to reach saturation and begin to condense into dew. Table 1.

Table 1 - Dew point

Vapor permeability- measured by the amount of water vapor passing through 1 m2 of area, 1 meter thick, for 1 hour, at a pressure difference of 1 Pa. (according to SNiP 23-02-2003). The lower the vapor permeability, the better the thermal insulation material.

Vapor permeability coefficient (DIN 52615) (mu, (mg/(m*h*Pa)) is the ratio of the vapor permeability of a layer of air 1 meter thick to the vapor permeability of a material of the same thickness

The vapor permeability of air can be considered as a constant equal to

0.625 (mg/(m*h*Pa)

The resistance of a layer of material depends on its thickness. The resistance of a material layer is determined by dividing the thickness by the vapor permeability coefficient. Measured in (m2*h*Pa) /mg

According to SP 50.13330.2012 "Thermal protection of buildings", Appendix T, table T1 "Designed thermal performance of building materials and products", the vapor permeability coefficient (mu, (mg / (m * h * Pa)) will be equal to:

Steel rod, reinforcing (7850kg/m3), coefficient. vapor permeability mu = 0;

Aluminum (2600) = 0; Copper (8500) = 0; Window glass (2500) = 0; Cast iron (7200) = 0;

Reinforced concrete (2500) = 0.03; Cement-sand mortar (1800) = 0.09;

Brickwork from hollow brick (ceramic hollow brick with a density of 1400 kg / m3 on cement sand mortar) (1600) = 0.14;

Brickwork from hollow brick (ceramic hollow brick with a density of 1300 kg / m3 on cement sand mortar) (1400) = 0.16;

Brickwork from solid brick (slag on cement sand mortar) (1500) = 0.11;

Brickwork made of solid brick (ordinary clay on cement sand mortar) (1800) = 0.11;

Expanded polystyrene boards with density up to 10 - 38 kg/m3 = 0.05;

Ruberoid, parchment, roofing felt (600) = 0.001;

Pine and spruce across the grain (500) = 0.06

Pine and spruce along the grain (500) = 0.32

Oak across grain (700) = 0.05

Oak along the grain (700) = 0.3

Plywood (600) = 0.02

sand for construction works(GOST 8736) (1600) = 0.17

Mineral wool, stone (25-50 kg / m3) = 0.37; Mineral wool, stone (40-60 kg/m3) = 0.35

Mineral wool, stone (140-175 kg / m3) = 0.32; Mineral wool, stone (180 kg/m3) = 0.3

Drywall 0.075; Concrete 0.03

The article is given for informational purposes.

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

The considered ability to pass, as well as retain water vapor, is characterized by special values ​​\u200b\u200bcalled the coefficient of resistance and vapor permeability.

At the moment, it is better to focus your own attention on the internationally established ISO standards. They determine the qualitative vapor permeability of dry and wet elements.

A large number of people are adherents of the fact 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 the wall is endowed with high vapor permeability, this does not mean that it becomes easy to breathe. A large amount of moisture is collected in the room, respectively, there is a low resistance to frost. Leaving through the walls, the vapors turn into ordinary water.

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

The most terrible moment is the fall of night temperature regimes, leading to a shift in the dew point in wall openings and further freezing of condensate. Subsequently, the resulting frozen waters begin to actively destroy the surface.

Indicators

The vapor permeability of materials table indicates the existing indicators:

1. , which is an energy type of heat transfer from highly heated particles to less heated ones. Thus, equilibrium is realized and appears in temperature conditions. With a high apartment thermal conductivity, you can live as comfortably as possible;
2. Thermal capacity calculates the amount of supplied and stored heat. It must necessarily be brought to a real volume. This is how temperature change is considered;
3. Thermal absorption is an 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-fledged comfort in the 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

Moisture located in the atmosphere, at a low level of relative humidity, is actively transported through the existing pores in building components. They acquire appearance, similar to individual water vapor molecules.

In those cases when the humidity begins to rise, the pores in the materials are filled with liquids, directing the working mechanisms for downloading into capillary suction. Vapor permeability begins to increase, lowering the resistance coefficients, with an increase in humidity in the building material.

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

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

Equipment

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

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