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

Most of the building materials are porous bodies. Pore \u200b\u200bsize and structure 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 materialsgiven by K.F. Fokin.

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

Straight line from 0 to point and curve 1 indicates a laminar air movement through the pores of a material with uniform porosity at small values \u200b\u200bof the pressure difference. Above this point, turbulent motion occurs on the curved section. In materials with different sizes pore air movement is turbulent even at a small pressure difference, which can be seen from the curvature of line 2. In low-air-permeable materials, on the contrary, air movement through the pores is laminar and at rather large pressure differences, therefore the dependence G from ΔР linear at any pressure difference (line 3). In wet materials (curve 4) at low ΔРless than a certain minimum pressure difference ΔP min, air permeability is absent, and only when this value is exceeded, when the pressure difference is sufficient to overcome the surface tension forces 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 following dependence is valid

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

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

δ - thickness of the material layer, m.

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

The values \u200b\u200bof the coefficient of air permeability 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 the formula (2.60), replace ΔРon ΔР n... Moreover, the exponent n varies within 0.5 - 1. However, in practice, formula (2.60) is also used for turbulent 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 by resistance to air permeability R and,kg / (m.h). with a pressure difference on different sides ∆Р о \u003d 10 Pa, which, with laminar air movement, is found by the formula:

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

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

In the values air permeability resistance for layers of some materials and structures.

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

Questions for self-control

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

2. What is air permeability?

3. What is infiltration?

4. What is exfiltration?

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

6. What are the two types of leaks through which air is filtered in fences?

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

8. What is the air permeability potential?

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

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

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

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

13. Write a formula for determining the air permeability resistance of a window.

During the construction process, any material must first of all be assessed according to its operational and technical characteristics. Solving the problem of building a “breathing” house, which is most typical for buildings made of brick or wood, or, on the contrary, to achieve maximum resistance to vapor permeability, you need to know and be able to operate with tabular constants to obtain the calculated parameters 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 the vapor permeability coefficient or vapor permeability resistance and is standardized by SNiP II-3-79 (1998) "Building heat engineering", namely by chapter 6 "Resistance to vapor permeability 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 of structures". Indicators of vapor permeability and thermal conductivity of the most common materials used for construction and insulation of buildings are presented in the table below.

Material	Density, kg / m3	Thermal conductivity, W / (m * C)	Water 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
Hollow ceramic bricks (gross 1000)
Hollow ceramic bricks (gross 1400)
Red clay brick
Brick, silicate
Linoleum
Minvata
Minvata
Foam concrete
Foam concrete
PVC foam
Expanded polystyrene
Expanded polystyrene
Expanded polystyrene
POLYSTYRENE ELECTRUDED
POLYURETHANE FOAM
POLYURETHANE FOAM
POLYURETHANE FOAM
POLYURETHANE FOAM
Foam glass
Foam glass
Sand
POLYUREA
POLYURETHANE MASTIC
Polyethylene
Roofing material, glassine
Pine, spruce along the grain
Pine, spruce across the grain
Plywood, glued

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

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

The values \u200b\u200bof the coefficient of resistance to vapor permeability 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 way on samples of building materials aged (not just released). Water vapor permeability was determined for building materials in dry and wet conditions.
In the domestic SNiP, only calculated data on vapor permeability are given for the mass ratio of moisture in the material w,%, equal to zero.
Therefore, for the choice of building materials for vapor permeability at summer cottage construction better focus on international ISO standards, which determine the vapor permeability of "dry" building materials with a moisture content of less than 70% and "wet" building materials with 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 internal layers of building materials will gradually "lock" 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 structures of buildings, layers with a higher thermal conductivity and greater resistance to vapor permeation than the outer layers should be placed on the warm side. According to T. Rogers (Rogers T.S. Designing thermal protection of buildings. / Translated 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 the inner surface with increasing ease will pass through all the spikes of the fence and be removed from the fence from the outer surface. The enclosing structure will function normally if, in compliance with the formulated principle, the vapor permeability of the outer layer is at least 5 times higher than the vapor permeability of the inner layer.

The mechanism of vapor permeability of building materials:

At low relative humidity, moisture from the atmosphere is in the form of individual water vapor molecules. When the relative humidity rises, 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 moisture content of the building material, its vapor permeability increases (the vapor permeability resistance coefficient decreases).

Vapor permeability values \u200b\u200bfor "dry" building materials according to ISO / FDIS 10456: 2007 (E) are applicable to the internal structures of heated buildings. Vapor permeability indicators of "wet" building materials are applicable for all external structures and internal structures of unheated buildings or country houses with a variable (temporary) heating mode.

Picture 1 - vapor permeability of a galvanized strip

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

Conclusion: the internal galvanized strip (see figure 1) can be installed in translucent structures without 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 for joints of galvanized sheet

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

Ensure that there is no vapor 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 moisture in the air (the content of water vapor 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 contained in it to reach saturation and begin to condense into dew. Table 1.

Table 1 - Dew point

Vapor permeability- is measured by the amount of water vapor passing through 1m2 of area, 1 meter thick, within 1 hour, with 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 an air layer 1 meter thick to the vapor permeability of a material of the same thickness

Air vapor permeability can be considered as a constant equal to

0.625 (mg / (m * h * Pa)

The resistance of the material layer depends on its thickness. The resistance of the 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 "Calculated thermal performance of building materials and products", the vapor permeability coefficient (mu, (mg / (m * h * Pa)) will be equal to:

Reinforcing bar steel (7850kg / m3), coefficient vapor permeability mu \u003d 0;

Aluminum (2600) \u003d 0; Copper (8500) \u003d 0; Window glass (2500) \u003d 0; Cast iron (7200) \u003d 0;

Reinforced concrete (2500) \u003d 0.03; Cement-sand mortar (1800) \u003d 0.09;

Brickwork from hollow bricks (ceramic hollow with a density of 1400 kg / m3 on cement sand mortar) (1600) \u003d 0.14;

Masonry from hollow bricks (ceramic hollow with a density of 1300 kg / m3 on a cement sand mortar) (1400) \u003d 0.16;

Brickwork made of solid bricks (slag on cement sand mortar) (1500) \u003d 0.11;

Brickwork made of solid bricks (ordinary clay on cement sand mortar) (1800) \u003d 0.11;

Plates from expanded polystyrene with a density of up to 10 - 38 kg / m3 \u003d 0.05;

Roofing material, parchment, roofing paper (600) \u003d 0.001;

Pine and spruce across the grain (500) \u003d 0.06

Pine and spruce along the grain (500) \u003d 0.32

Oak across the grain (700) \u003d 0.05

Oak along the grain (700) \u003d 0.3

Plywood (600) \u003d 0.02

Sand for construction works (GOST 8736) (1600) \u003d 0.17

Minvata, stone (25-50 kg / m3) \u003d 0.37; Mineral wool, stone (40-60 kg / m3) \u003d 0.35

Minvata, stone (140-175 kg / m3) \u003d 0.32; Mineral wool, stone (180 kg / m3) \u003d 0.3

Drywall 0.075; Concrete 0.03

The article is given for informational purposes only.

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

The considered ability to transmit and also 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 high-quality vapor permeability of dry and wet elements.

A large number of people adhere to the belief that breathers are 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 breathing becomes easy. A large amount of moisture is collected in the room, respectively, a low resistance to frost appears. Coming out through the walls, the vapors turn into ordinary water.

Most manufacturers, when calculating the indicator under consideration, 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 five times, therefore, it will be quite cold in an apartment or other room.

The most frightening moment is the drop in night temperature regimes, leading to a shift in the dew point in wall openings and further freezing of condensate. Subsequently, the formed frozen water begins to actively destroy the surface.

Indicators

The vapor permeability of materials the table indicates the existing indicators:

1. , which is an energetic form 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. The thermal capacity calculates the amount of heat supplied and stored. It must be brought to the real volume without fail. This is how temperature change is viewed;
3. Thermal assimilation is the enclosing structural alignment in temperature fluctuations, that is, the degree of moisture absorption by wall surfaces;
4. Thermal stability is a property that protects structures from sharp thermal vibrational flows. Absolutely all full-fledged comfort in the room depends on the general thermal conditions. Thermal stability and capacitance can be active when the layers are made of materials with increased heat absorption. Stability provides a normalized state of structures.

Vapor permeability mechanisms

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

In cases where the moisture begins to rise, the pores in the materials fill with fluids, directing the mechanisms of operation to download in capillary suction. Vapor permeability begins to increase, lowering the resistance coefficients, with an increase in moisture 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 an outdoor version of structures.

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

Equipment

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

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