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 committed to the fact that breathing is a 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, an equilibrium in temperature regimes is carried out and appears. 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 take on an 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.

Everyone knows that a comfortable temperature regime, and, accordingly, a favorable microclimate in the house is ensured largely due to high-quality thermal insulation. Recently, there has been a lot of debate about what ideal thermal insulation should be and what characteristics it should have.

There are a number of properties of thermal insulation, the importance of which is beyond doubt: these are thermal conductivity, strength and environmental friendliness. It is quite obvious that effective thermal insulation must have a low coefficient of thermal conductivity, be strong and durable, and not contain substances harmful to humans and the environment.

However, there is one property of thermal insulation that raises a lot of questions - this is vapor permeability. Should the insulation be permeable to water vapor? Low vapor permeability - is it an advantage or a disadvantage?

Points for and against"

Supporters of cotton wool insulation claim that high vapor permeability is a definite plus, vapor-permeable insulation will allow the walls of your house to "breathe", which will create a favorable microclimate in the room even in the absence of any additional ventilation system.

Adepts of penoplex and its analogues say: the insulation should work like a thermos, and not like a leaky "quilted jacket". In their defense, they make the following arguments:

1. Walls are not the "breathing organs" of the house at all. They perform a completely different function - they protect the house from environmental influences. The respiratory system for the house is the ventilation system, as well as, in part, windows and doorways.

In many European countries, supply and exhaust ventilation is installed without fail in any residential area and is perceived as the same norm as a centralized heating system in our country.

2. The penetration of water vapor through walls is a natural physical process. But at the same time, the amount of this penetrating steam in a residential area with normal operation is so small that it can be ignored (from 0.2 to 3% * depending on the presence / absence of a ventilation system and its effectiveness).

* Pogozhelsky J.A., Kasperkevich K. Thermal protection of multi-panel houses and energy saving, planned topic NF-34/00, (typescript), ITB library.

Thus, we see that high vapor permeability cannot act as a cultivated advantage when choosing a thermal insulation material. Now let's try to find out if this property can be considered a disadvantage?

Why is the high vapor permeability of the insulation dangerous?

In winter, at sub-zero temperatures outside the house, the dew point (the conditions under which water vapor reaches saturation and condenses) should be in the insulation (extruded polystyrene foam is taken as an example).

Fig. 1 Dew point in XPS slabs in houses with insulation cladding

Fig. 2 Dew point in XPS slabs in frame-type houses

It turns out that if the thermal insulation has a high vapor permeability, then condensate can accumulate in it. Now let's find out why the condensate in the heater is dangerous?

First of all, when condensation forms in the insulation, it becomes wet. Accordingly, its thermal insulation characteristics decrease and, conversely, thermal conductivity increases. Thus, the insulation begins to perform the opposite function - to remove heat from the room.

A well-known expert in the field of thermal physics, Doctor of Technical Sciences, Professor, K.F. Fokin concludes: “Hygienists consider the air permeability of fences as a positive quality that provides natural ventilation of the premises. But from a thermotechnical point of view, the air permeability of fences is rather a negative quality, since in winter time infiltration (air movement from inside to outside) causes additional heat loss by fences and cooling of rooms, and exfiltration (air movement from outside to inside) can adversely affect the humidity regime of external fences. promoting moisture condensation.

In addition, in SP 23-02-2003 "Thermal protection of buildings", section No. 8, it is indicated that the air permeability of enclosing structures for residential buildings should be no more than 0.5 kg / (m²∙h).

Secondly, due to wetting, the heat insulator becomes heavier. If we are dealing with a cotton insulation, then it sags, and cold bridges form. In addition, the load on the supporting structures increases. After several cycles: frost - thaw, such a heater begins to collapse. To protect the moisture-permeable insulation from getting wet, it is covered with special films. A paradox arises: the insulation breathes, but it needs protection with polyethylene or a special membrane that negates all its “breathing”.

Neither polyethylene nor the membrane allows water molecules to pass into the insulation. It is known from a school physics course that air molecules (nitrogen, oxygen, carbon dioxide) are larger than a water molecule. Accordingly, air is also unable to pass through such protective films. As a result, we get a room with a breathable insulation, but covered with an airtight film - a kind of greenhouse made of polyethylene.

In order to destroy it

Calculations of units of vapor permeability and resistance to vapor permeability. Technical characteristics of membranes.
Often, instead of the Q value, the vapor permeability resistance value is used, in our opinion it is Rp (Pa * m2 * h / mg), foreign Sd (m). Vapor permeability is the reciprocal of Q. Moreover, imported Sd is the same Rp, only expressed as an equivalent diffusion resistance to vapor permeability of an air layer (equivalent diffusion thickness of air).
Instead of further reasoning in words, we correlate Sd and Rn numerically.
What does Sd=0.01m=1cm mean?
This means that the diffusion flux density with a difference dP is:
J=(1/Rp)*dP=Dv*dRo/Sd
Here Dv=2.1e-5m2/s diffusion coefficient of water vapor in air (taken at 0°C)/
Sd is our very Sd, and
(1/Rp)=Q
Let's transform the right equality using the ideal gas law (P*V=(m/M)*R*T => P*M=Ro*R*T => Ro=(M/R/T)*P) and see.
1/Rp=(Dv/Sd)*(M/R/T)
Hence Sd=Rp*(Dv*M)/(RT) which is not clear to us yet
To get the correct result, you need to represent everything in units of Rp,
more precisely Dv=0.076 m2/h
M=18000 mg/mol - molar mass of water
R=8.31 ​​J/mol/K - universal gas constant
T = 273K - temperature on the Kelvin scale, corresponding to 0 degrees C, where we will carry out calculations.
So, substituting everything, we have:
sd= Rp*(0.076*18000)/(8.31*273) \u003d 0.6 Rp or vice versa:
Rp=1.7Sd.
Here Sd is the same imported Sd [m], and Rp [Pa * m2 * h / mg] is our resistance to vapor permeation.
Also Sd can be associated with Q - vapor permeability.
We have that Q=0.56/Sd, here Sd [m] and Q [mg/(Pa*m2*h)].
Let us check the obtained relations. To do this, take the technical characteristics of various membranes and substitute.
To begin with, I will take the data on Tyvek from here
As a result, the data is interesting, but not very suitable for formula testing.
In particular, for the Soft membrane we obtain Sd=0.09*0.6=0.05m. Those. Sd in the table is underestimated by 2.5 times or, accordingly, Rp is overestimated.

I take further data from the Internet. By Fibrotek membrane
I will use the last pair of data permeability, in this case Q*dP=1200 g/m2/day, Rp=0.029 m2*h*Pa/mg
1/Rp=34.5 mg/m2/h/Pa=0.83 g/m2/day/Pa
From here we will extract the difference in absolute humidity dP=1200/0.83=1450Pa. This humidity corresponds to a dew point of 12.5 degrees or a humidity of 50% at 23 degrees.

On the Internet, I also found on another forum the phrase:
Those. 1740 ng/Pa/s/m2=6.3 mg/Pa/h/m2 corresponds to vapor permeability ~250 g/m2/day.
I'll try to get that ratio myself. It is mentioned that the value in g/m2/day is also measured at 23 deg. We take the previously obtained value dP=1450Pa and we have an acceptable convergence of the results:
6.3*1450*24/100=219 g/m2/day Hurrah Hurrah.

So, now we are able to correlate the vapor permeability that you can find in the tables and the resistance to vapor permeability.
It remains to make sure that the relation between Rp and Sd obtained above is correct. I had to dig and found a membrane for which both values ​​are given (Q * dP and Sd), while Sd is a specific value, and not "no more". Perforated membrane based on PE film
And here is the data:
40.98 g/m2/day => Rp=0.85 =>Sd=0.6/0.85=0.51m
Again it doesn't fit. But in principle, the result is not far off, which, given the fact that it is not known at what parameters, the vapor permeability is determined is quite normal.
Interestingly, according to Tyvek they got misalignment in one direction, according to IZOROL in the other. Which suggests that you can’t trust some values ​​​​everywhere.

PS I would be grateful for the search for errors and comparisons with other data and standards.

Vapor permeability of walls - get rid of fiction.

In this article, we will try to answer the following frequently asked questions: what is vapor permeability and whether vapor barrier is needed when building the walls of a house 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 of the cement-sand mortar is more than 1.5 times lower than that of 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 material layer 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 material layer, characterized by the vapor permeability coefficient 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 water vapor diffusion resistance coefficient is a dimensionless value showing how many times clean air is more permeable to vapor than any 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:

"The resistance to vapor permeability of air layers in building envelopes 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 of the wall structure matters. 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, it is impossible to veneer gas silicate blocks with a thickness of 200 mm with clinker tiles with a thickness of 14 mm. With this ratio of materials and their thicknesses, the ability to pass vapors from the finishing material will be 70% less than that of the blocks. If the thickness of the load-bearing wall is 400 mm, and the tiles are still 14 mm, then the situation will be the opposite and the ability to let through pairs of tiles will be 15% greater 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:

If ceramic tiles are used for facade decoration, 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 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 wall lined with ceramic tiles 20 mm thick, the thickness of the bearing wall made of gas silicate blocks with a density of D500 must be less than 60 mm, which contradicts SNiP 3.03.01-87 "Bearing and enclosing structures" p. the minimum thickness of the bearing wall is 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 is a 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. The 2nd layer - ordinary 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.

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 using clinker bricks, a ventilation gap is required:

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 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.

Dew point - 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 "Calculated 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 work (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.