The vapor permeability of the material is expressed in its ability to skip water vapor. This property is to resist the penetration of the steam or allow it to pass through the material is determined by the level of parry permeability coefficient, which is denoted by μ. This value that sounds like "MJ" acts as the relative size of the resistance to the parameter of steam in comparison with the characteristics of air resistance.
There is a table that reflects the ability of material to steam plane, it can be seen in Fig. 1. Thus, the value of the MJ for mineral wool is 1, this indicates that it is capable of passing water steam as well as the air itself. While this value for aerated concrete is 10, it means that it copes with a pair of 10 times worse than air. If the MJ indicator is multiplied by a layer thickness expressed in meters, this will allow to obtain an SD air thickness equal to parry permeability (M).
It can be seen from the table that for each position, the record indicator is indicated at different state. If you look into the SNiP, you can see the calculated data of the indicator of the MJ with the ratio of moisture in the body of the material equal to zero.
Figure 1. Parry permeability table of building materials
For this reason, when purchasing goods that are supposed to be used in the process of country construction, it is preferable to take into account international ISO standards, since they determine the MJ indicator in a dry state, with a humidity level of no more than 70% and humidity indicator more than 70%.
When choosing building materials, which will be based on a multilayer structure, the indicator of the MJ layers from the inside should be lower, otherwise, with time inside the layers, the layers will become wet, as a result of this they will lose their thermal insulation qualities.
When creating enclosing structures, you need to take care of their normal functioning. To do this, you should follow the principle that it states that the level of the MJ of the material, which is located in the outer layer, should be 5 times or more to exceed the mentioned indicator of the material in the inner layer.
Parry permeability mechanism
Under the conditions of a minor relative humidity, moisture particle, which are contained in the atmosphere, penetrate through the pores of the building materials, turning out there in the form of steam molecules. At the time of increasing the level of relative humidity of the pores of the layers, water accumulates, which becomes the cause of wetting and capillary suction.
At the time of increasing the level of humidity of the layer, its indicator of the MJ increases, thus, the level of vapor permeability resistance is reduced.
Indicators of vapor permeability of non-resistant materials are applicable under conditions of internal structures of buildings that have heating. But the levels of vapor permeability of moisturized materials are applicable for any construction designs that are not heated.
Parry permeability levels that are part of our norms, not in all cases are equivalent to indicators that belong to international standards. Thus, in domestic SNIP, the level of Ceramzito- and slagobetone is almost no different, while according to international standards, the data differ from each other 5 times. The levels of vapor permeability of GLC and slagobetone in domestic standards are almost the same, and in international standards, the data is characterized by 3 times.
There are various ways to determine the level of vapor permeability, as for the membranes, then the following methods can be distinguished:
- American test with vertically mounted bowl.
- American test with an inverted bowl.
- Japanese test with a vertical bowl.
- Japanese test with an inverted bowl and moisture maker.
- American test with a vertical bowl.
The Japanese test uses a dry moisture maker, which is located under the test material. All tests use a sealing element.
Everyone knows that comfortable temperature, and, accordingly, a favorable microclimate in the house is ensured in many respects due to high-quality thermal insulation. Recently, there are a lot of disputes about what should be the perfect thermal insulation and what characteristics it should have.
There are a number of properties of thermal insulation, the importance of which is no doubt: it is thermal conductivity, strength and environmental friendliness. It is obvious that effective thermal insulation should have a low thermal conductivity coefficient, being durable and durable, not contain substances harmful to humans and the environment.
However, there is one property of thermal insulation, which causes a lot of questions - it is vapor permeability. Should the insulation flow to water vapor? Low vapor permeability - is this or disadvantage?
Points for and against"
Supporters of cotton insulation assure that high steam-permeable ability is a certain plus, a vapor-permeable insulation will allow the walls of your home to "breathe", which will create a favorable microclimate in the room, even in the absence of any additional ventilation system.
The adepts of Polyeplex and its analogs declare: the insulation must work as a thermos, and not as a holey "vicar". In their defense, they lead the following arguments:
1. Walls are not at all "respiratory authorities" at home. They perform a completely different function - protect the house from environmental exposure. The respiratory authorities for the house is the ventilation system, as well as partially, windows and doorways.
In many European countries, the supply and exhaust ventilation is mandatory in any residential room and is perceived as the same norm as the centralized heating system in our country.
2. Penetration of water vapor Through the walls is a natural physical process. But at the same time, the amount of this penetrating steam in the residential room with the usual operating mode is so little that it can not be taken into account (from 0.2 to 3% * depending on the presence / absence of a ventilation system and its effectiveness).
* Pogodelski Y.A., Kaspirkevich K. Thermal protection of multiphanner homes and energy savings, planned theme NF-34/00, (typewrition), 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 is considered a disadvantage?
What is dangerous high vapor permeability of the insulation?
In winter, during the minus temperature outside the house, the dew point (conditions under which water steam reaches saturation and condensed) must be in the insulation (extruded polystyrene foam is taken as an example).
Fig.1 Dew point in Epps plates in houses with facing by insulation
Fig.2 Dew point in Epps plates in frame-type houses
It turns out that if the thermal insulation has high vapor permeability, condensate can accumulate in it. Now find out what condensate is dangerous in insulation?
Firstly, When forming in a condensate insulation, it becomes wet. Accordingly, its thermal insulation characteristics decreases and, on the contrary, the thermal conductivity increases. Thus, the insulation begins to perform the opposite function - remove heat out of the room.
Famous in the field of thermal physics expert, Doctor, Professor, K.F. Fokin concludes: "The hygienists consider the air permeability of the fences as a positive quality, providing natural ventilation of the premises. But from a heat engineering point of view, the air permeability of the fences is rather negative quality, since in winter the infiltration (air traffic from the inside) causes additional heat losses with fences and cooling rooms, and the exhaustion (air movement outside the outside) may adversely affect the humidity mode of external fences , contributing to moisture condensation. "
In addition, the SP 23-02-2003 "Thermal Protection of Buildings" section No. 8 states that the breathability of enclosing structures for residential buildings should be no more than 0.5 kg / (m² ∙ h).
Secondly, due to wetting, the thermal insulator is dried. If we are dealing with a cottonier insulation, then he sends, and cold bridges are formed. In addition, the load on the supporting structures is increasing. After a few cycles: Frost - a thaw such insulation begins to collapse. To protect the moisture-permeable insulation from wetting it is covered with special films. A paradox arises: the insulation breathes, but it requires protection with polyethylene, or a special membrane that reduces all its "breathing".
Neither polyethylene nor the membrane passes the water molecules into the insulation. From the school year of physics, it is known that air molecules (nitrogen, oxygen, carbon dioxide) is greater than the water molecule. Accordingly, the air is also not capable of passing through such protective films. As a result, we get a room with a breathable insulation, but a airtight film coated - a kind of greenhouse from polyethylene.
The concept of "breathable walls" is considered the positive characteristic of the materials from which they are made. But few people think about the reasons allowing this breathing. Materials capable of passing both air and steam are vapor permeable.
A good example of building materials with high steam permeability:
- wood;
- clay plates;
- foam concrete.
Concrete or brick walls are less permeable for steam than wooden or clay.
Sources of pair indoors
Human respiration, cooking, water vapor from the bathroom and many other steam sources in the absence of an exhaust device create a high level of humidity indoors. Often you can observe the formation of Spains on window windows in winter, or on cold water pipes. These are examples of the formation of water vapor inside the house.
What is vapor permeability
The design and construction rules give the following definition of the term: the vapor permeability of materials is the ability to skip the moisture droplets contained in the air due to the different values \u200b\u200bof the partial pressure of steam from opposite sides with the same air pressure values. It is also defined as the density of the steam stream passing through a certain thickness of the material.
A table that has a vapor permeability coefficient, composed for building materials, is conditional in nature, since the specified calculated moisture values \u200b\u200band atmospheric conditions do not always correspond to real conditions. The dew point can be calculated based on approximate data.
Station of walls taking into account vapor permeability
Even if the walls are erected from a material having high vapor permeability, it cannot be a guarantee that it will not turn into water in the thickness of the wall. That this does not happen, you need to protect the material from the difference in the partial pressure of vapors from the inside and outside. Protection against the formation of steam condensate is performed using OSB plates, insulation materials of the type of polyplex and pairsproof films or membranes, preventing steam penetration into the insulation.
The walls are insulated with the calculation so that a layer of insulation is closer to the outer edge, which is unable to form moisture condensation, moving the dew point (water formation). In parallel with protective layers in the roofing cake, it is necessary to ensure the correct ventilation gap.
Destructive actions of a para
If the wall cake has a weak ability to absorb steam, it does not threaten the destruction due to the expansion of moisture from the frost. The main condition is to prevent moisture accumulation in the thickness of the wall, but to ensure its free passage and weathering. It is equally important to arrange a forced exhaust of excess moisture and steam out of the room, connect a powerful ventilation system. Observing the listed conditions, you can protect the walls from cracking, and increase the service life of the whole house. Permanent passage of moisture through building materials accelerates their destruction.
Use of conductive qualities
Given the peculiarities of the operation of buildings, the following insulation principle is applied: the most steam-conducting insulation materials are located outside. Due to this location of the layers, the likelihood of water accumulation is reduced by reducing the temperature on the street. So that the walls are not wet from the inside, the inner layer is insulated with a low vapor permeability material, for example, a thick layer of extruded polystyrene foam.
The opposite method of using steaming effects of building materials is successfully applied. It consists in the fact that the brick wall is covered with a steam-eyed foam glass layer, which interrupts the moving flow of a pair from the house to the street during a period of low temperatures. The brick begins to accumulate the humidity of the rooms, creating a pleasant climate indoors due to a reliable steam barrier.
Compliance with the basic principle when building walls
The walls should be minimal to carry out steam and heat, but at the same time be heat and heat resistant. When using the material of one type of required effects, it is impossible to achieve. The outer wall part is obliged to delay the cold masses and prevent their impact on internal heat-insulated materials that retain the comfortable thermal regime inside the room.
For the inner layer, the reinforced concrete is perfect, its heat capacity, density and strength have maximum indicators. Concrete successfully smoothes the difference in night and daytime temperature differences.
When conducting construction works, wall pies are made by the basic principle: the vapor permeability of each layer should be increased in the direction of the inner layers to the outer.
Rules for the location of vaporizolizing layers
To ensure the best performance characteristics of multilayer structures of structures, a rule applies: from the side having a higher temperature, materials with increased resistance to steam penetration with increased thermal conductivity. Layers located outside should have high steps. For the normal functioning of the enclosing structure, it is necessary that the coefficient of the outer layer five times exceeds the indicator of the layer located inside. 
When performing this rule, water vapors that fell into the warm layer of the wall will not work with acceleration to exit the outside through more porous materials.
If this condition fails to comply with this condition, the internal layers of building materials are closed and become heavily conducted.
Familiarity with table vapor permeability materials
When designing the house, the characteristics of the building raw materials are taken into account. The rules set contains a table with information about which coefficient of parry permeability has construction materials under conditions of normal atmospheric pressure and an average air temperature.
Material | Parry permeability coefficient |
extruded expanded polystyrene foam | |
polyurene Foolder | |
mineral wool | |
reinforced concrete, concrete | |
pine or spruce | |
ceramzit | |
foam concrete, aerated concrete | |
granite, marble | |
plasterboard | |
chipboard, osp, fiberboard | |
foamglo | |
ruberoid | |
polyethylene | |
linoleum |
The importance of the vapor permeability table of materials
Parry permeability coefficient is an important parameter that is used to calculate the thickness of the layer of insulation materials. The quality of the insulation of the entire design depends on the performance of the results.
Sergey Novozhilov - expert on roofing materials with 9 years of practical experience in the field of engineering solutions in construction.
Often, expression is found in construction articles - the vapor permeability of concrete walls. It means the ability of the material to skip water vapors, in popular - "breathe". This parameter is of great importance, as in the residential room there are constantly formed products of life, which must be constantly output.
General
If you do not create normal ventilation in the room, it will create dampness, which will lead to the appearance of fungus and mold. Their allocation can bring harm to our health.
On the other hand, vapor permeability affects the ability of the material to accumulate moisture. This is also a bad indicator, since the more he can hold it in itself, the higher the likelihood of fungus, putrefactive manifestations, as well as damage during freezing.
Parry permeability denote the Latin letter μ and are measured in mg / (m * h * pa). The amount shows the amount of water vapor, which can pass through the wall material on the square 1 m 2 and with its thickness 1 m in 1 hour, as well as the difference between the outer and internal pressure of 1 pa.
High ability of water vapor from:
- foam concrete;
- aerated concrete;
- perliteobetona;
- keramzitobetone.
Closes the table - heavy concrete.
Tip: If you need to make a technological channel in the foundation, the diamond drilling of the holes in the concrete will help you.
Gasobutton
- The use of a material as a enclosing structure makes it possible to avoid accumulation of unnecessary moisture inside the walls and maintain its heat-saving properties, which will prevent possible destruction.
- Any gas-concrete and foam concrete block has an ≈ 60% air in its composition, due to which the vapor permeability of the aerated concrete is recognized on a good smooth, the walls in this case can "breathe".
- Water pairlessly seep through the material, but not condensed in it.
Parry permeability of aerated concrete, as well as foam concrete, significantly exceeds heavy concrete - at the first 0.18-0.23, in the second - (0.11-0.26), in the third - 0.03 mg / m * h * PA.
Especially it would be especially necessary to emphasize that the structure of the material provides him with an effective removal of moisture into the environment, so that even when the material is freezing, it is not destroyed - it is supplanted out through open pores. Therefore, preparing, this feature should be taken into account and select the appropriate plasters, putty and paints.
The instruction is strictly regulating that their parameters of vapor permeability were not lower than aerated concrete blocks used for construction.
Tip: Do not forget that the parameters of vapor permeability depends on the density of aerated concrete and may differ in half.
For example, if you use D400 - they have a coefficient equal to 0.23 mg / m n per, and the D500 is already below - 0.20 mg / m. In the first case, the numbers suggest that the walls will have a higher "breathable" ability. So, when selecting finishing materials for walls from aerated concrete D400, make sure that they have the parry permeability ratio of the same or higher.
Otherwise, this will lead to a worsening of moisture removal from the walls, which will affect the decline in the level of comfort of living in the house. It should also be considered that if you were applied to the outer decoration vapor-permeable paint for aerated concrete, and for internal - unpaid materials, steam will simply accumulate indoors, making it wet.
Ceramzitobeton
The vapor permeability of ceramzite concrete blocks depends on the amount of filler in its composition, namely the ceramisite - foamed baked clay. In Europe, such products are called eco-or bobelocles.
Tip: If you do not work out, cut the ceramzitoblock in the usual circle and grinder, use diamond.
For example, cutting reinforced concrete diamond circles makes it possible to quickly solve the task.
Polystyrevbeton
The material is another representative of cellular concrete. Parical permeability of polystyrene bapton is usually equal to the tree. You can make it with your own hands.
Today more attention begins to be given not only to the thermal properties of wall structures, and the comfort of living in the construction. On thermal inertness and vapor permeability, polystyrene concrete reminds wooden materials, and it is possible to achieve heat transfer resistance by changing its thickness. Therefore, the filling monolithic polystyrene is usually used, which is cheaper than finished plates.
Output
From the article you learned that there is such a parameter for building materials as vapor permeability. It makes it possible to remove moisture outside the walls of the structure, improving their strength and characteristics. Parry permeability of foam concrete and aerated concrete, as well as heavy concrete is distinguished by its indicators, which must be considered when choosing finishing materials. The video in this article will help you find additional information on this topic.
In order to distinguish
Calculations of vapor permeability and resistance of vapor permeation. Technical characteristics of membranes.
Often, instead of the quantity q, the amount of resistance to vapor permeation is used, in our opinion it is RP (PA * M2 * C / mg), foreign SD (M). Parry permeation resistance Reverse quantity Q. With the volume of imported SD is the same RP, only expressed in the form of an equivalent diffusion resistance of the air-based air layer (equivalent diffusion thickness of air).
Instead of reasoning with the words SD and RP numerically.
What does sd \u003d 0.01m \u003d 1 cm mean?
This means that the density of the diffusion stream with DP drop is:
J \u003d (1 / rp) * dp \u003d dv * dro / sd
Here dv \u003d 2,1e-5m2 / with water vapor diffusion coefficient in air (taken at 0GRADC) /
SD is our SD, and
(1 / Rp) \u003d Q
We transform the right equality Taking advantage of the law of the perfect gas (P * V \u003d (M / M) * R * T \u003d\u003e P * M \u003d R * R * T \u003d\u003e RO \u003d (M / R / T) * P) and see.
1 / RP \u003d (DV / SD) * (M / R / T)
From here until the SD \u003d RP * (DV * M) / (RT)
To get a sure result you need to imagine in units RP,
More precisely dv \u003d 0.076 m2 / h
M \u003d 18000 mg / mol - molar mass of water
R \u003d 8,31 J / mol / K - Universal Gas Permanent
T \u003d 273К - The temperature on the Kelvin scale corresponding to 0GRADC where we will conduct calculations.
So, all substituting:
SD \u003d.RP * (0.076 * 18000) / (8,31 * 273) \u003d 0.6RP or vice versa:
RP \u003d 1.7SD.
Here SD is the same imported SD [M], and RP [PA * M2 * C / mg] - our resistance to vapor permeation.
Also, SD can be associated with q - vapor permeability.
We have that Q \u003d 0.56 / SD, here SD [M], and q [mg / (Pa * m2 * h)].
Check the obtained ratios. To do this, take the technical characteristics of various membranes and substitute.
To start, take the data on Tyvek from here
The data are assessed interesting, but not very suitable for the formulas.
In particular, the SOFT membrane we obtain SD \u003d 0.09 * 0.6 \u003d 0.05m. Those. The SD in the table is adjusted 2.5 times or, according to RP.
I take on the data from the Internet expanses. On the fibrotek membrane
Understand the last pair of data permeability, in this case Q * dp \u003d 1200 g / m2 / day, Rp \u003d 0.029 m2 * h * PA / mg
1 / Rp \u003d 34.5 mg / m2 / h / pa \u003d 0.83 g / m2 / day / pa
Hence the absolute moisture drop dp \u003d 1200 / 0.83 \u003d 1450pa. This humidity corresponds to the dew point of 12,5,5 or humidity 50% at 23rd.
On the Internet also discovered the phrase on another forum:
Those. 1740 Ng / PA / C / m2 \u003d 6.3 mg / P / C / m2 corresponds to vapor permeability ~ 250g / m2 / day.
I will try to get such a ratio itself. It is mentioned that the value in g / m2 / day is measured including at 23rd. We carry out the previously obtained value of DP \u003d 1450Pa and we have acceptable convergence of results:
6.3 * 1450 * 24/100 \u003d 219 g / m2 / day. Hurrah Hurrah.
So, now we can correlate the vapor permeability that can meet in tables and resistance to vapor permeation.
It also remains to be sure that the ratio between RP and SD is true. I had to rode and found the membrane for which both quantities are given (Q * DP and SD), while the SD is a specific value, and not "not more". Perforated PE Film Based Membrane
And here is the data:
40.98 g / m2 / day \u003d\u003e Rp \u003d 0.85 \u003d\u003e Sd \u003d 0.6 / 0.85 \u003d 0.51m
Again does not converge. But in principle, the result is not far from the remarks that considering that it is unknown under which parameters the vapor permeability is determined quite normal.
What is interesting, by Tyvek got the unrest in one direction, according to Izorol to another. What does not mean that everywhere some values \u200b\u200bare impossible.
PS I will be grateful for the search for errors and comparisons with other data and regulations.