The term "vapor permeability" itself indicates the property of materials to transmit or retain water vapor in their thickness. The table of vapor permeability of materials is conditional, since the given calculated values of the moisture level and atmospheric impact do not always correspond to reality. The dew point can be calculated according to the average value.
Each material has its own percentage of vapor permeability
Determination of the level of vapor permeability
In the arsenal professional builders there are special technical means which allow with high precision diagnose the vapor permeability of a particular building material. To calculate the parameter, the following tools are used:
- devices that make it possible to accurately determine the thickness of the layer of building material;
- laboratory glassware for performing research;
- scales with the most accurate readings.
In this video you will learn about vapor permeability:
With the help of such tools, you can correctly determine the desired characteristic. Since the experimental data are entered into the tables of the vapor permeability of building materials, during the preparation of the dwelling plan, there is no need to establish the vapor permeability of the building materials.
Creation of comfortable conditions
To create a favorable microclimate in a home, it is required to take into account the characteristics of the building materials used. Particular emphasis should be placed on vapor permeability. Having knowledge about this ability of the material, it is possible to correctly select the raw materials necessary for the construction of housing. Data is taken from building codes and rules, for example:
- vapor permeability of concrete: 0.03 mg / (m * h * Pa);
- vapor permeability of fiberboard, particleboard: 0.12-0.24 mg / (m * h * Pa);
- vapor permeability of plywood: 0.02 mg / (m * h * Pa);
- ceramic bricks: 0.14-0.17 mg / (m * h * Pa);
- silicate brick: 0.11 mg / (m * h * Pa);
- roofing material: 0-0.001 mg / (m * h * Pa).
Steam generation in a residential building can be caused by human and animal breathing, food preparation, temperature changes in the bathroom, and other factors. Absence exhaust ventilation also creates a high degree of humidity in the room. V winter period it is not uncommon to notice the formation of condensation on the windows and on the cold piping. it illustrative example the appearance of steam in residential buildings.
Protection of materials in the construction of walls
Building materials with high permeability steam cannot fully guarantee the absence of condensation inside the walls. In order to prevent water accumulation in the depths of the walls, a pressure difference of one of the component parts mixtures of gaseous elements of water vapor on both sides of the building material.
Provide protection against the appearance of liquid realistically, using oriented strand board (OSB), insulation materials such as penoplex and a vapor barrier film or a membrane that prevents steam from seeping into the insulation. At the same time with protective layer you need to organize the correct air gap for ventilation.
If wall cake there is no sufficient capacity to absorb steam, it does not run the risk of being destroyed as a result of the expansion of condensate from low temperatures... The main requirement is to prevent the accumulation of moisture inside the walls and provide it with unhindered movement and weathering.
An important condition is the installation ventilation system with forced draft which will not allow to accumulate excess fluid and a couple indoors. By fulfilling the requirements, you can protect the walls from cracking and increase the durability of the dwelling as a whole.
The location of the thermal insulation layers
To provide the best performance characteristics multi-layer structures are used following rule: side with more high temperature provided by materials with increased resistance to steam infiltration with a high coefficient of thermal conductivity.
The outer layer must have a high vapor permeability. For normal operation of the enclosing structure, it is necessary that the index of the outer layer is five times higher than the values of the inner layer. Subject to this rule, water vapor trapped in the warm layer of the wall, without special efforts leave it through more cellular building materials. Neglecting these conditions, the inner layer of building materials becomes damp, and its thermal conductivity coefficient becomes higher.
The selection of finishes also plays an important role in final stages construction works... The correctly selected composition of the material guarantees him the effective removal of liquid into external environment, so even with sub-zero temperature the material will not collapse.
The vapor permeability index is a key indicator when calculating the size of the cross-section of the insulation layer. The reliability of the calculations made will determine how high-quality the insulation of the entire building will turn out.
V recent times more and more use in construction is finding a variety of external insulation systems: "wet" type; ventilated facades; modified well masonry, etc. All of them are united by the fact that these are multi-layer enclosing structures. And for multi-layer structures, questions vapor permeability layers, moisture transfer, quantify condensation water is of paramount importance.
As practice shows, unfortunately, both designers and architects do not pay due attention to these issues.
We have already noted that the Russian construction market oversaturated with imported materials. Yes, of course, the laws of building physics are the same, and they operate in the same way, for example, both in Russia and in Germany, but the methods of approach and the regulatory framework are very often very different.
Let us explain this by the example of vapor permeability. DIN 52615 introduces the concept of vapor permeability through the vapor permeability coefficient μ and air equivalent gap s d .
If we compare the vapor permeability of an air layer with a thickness of 1 m with the vapor permeability of a layer of material of the same thickness, then we obtain the vapor permeability coefficient
μ DIN (dimensionless) = vapor permeability of air / vapor permeability of material
Compare, the concept of vapor permeability coefficient μ SNiP in Russia is introduced through SNiP II-3-79 * "Construction heat engineering", has the dimension mg / (m * h * Pa) and characterizes the amount of water vapor in mg that passes through one meter of the thickness of a particular material in one hour at a pressure difference of 1 Pa.
Each layer of material in the structure has its own final thickness d, m. It is obvious that the amount of water vapor passing through this layer will be the less, the greater its thickness. If we multiply μ DIN and d, then we get the so-called air equivalent gap or diffusely equivalent thickness of the air layer s d
s d = μ DIN * d[m]
Thus, according to DIN 52615, s d characterizes the thickness of the air layer [m], which has equal vapor permeability with a layer of a specific material with a thickness d[m] and vapor permeability coefficient μ DIN... Resistance to vapor permeation 1 / Δ defined as
1 / Δ = μ DIN * d / δ in[(m² * h * Pa) / mg],
where δ in- coefficient of vapor permeability of air.
SNiP II-3-79 * "Construction heat engineering" determines the resistance to vapor permeation R P how
R P = δ / μ SNiP[(m² * h * Pa) / mg],
where δ - layer thickness, m.
Compare, according to DIN and SNiP vapor permeability resistance, respectively, 1 / Δ and R P have the same dimension.
We have no doubt that our reader already understands that the question of linking quantitative indicators of the vapor permeability coefficient according to DIN and SNiP lies in determining the vapor permeability of air δ in.
According to DIN 52615 air vapor permeability is defined as
δ in = 0.083 / (R 0 * T) * (p 0 / P) * (T / 273) 1.81,
where R 0- gas constant of water vapor equal to 462 N * m / (kg * K);
T- indoor temperature, K;
p 0- average air pressure inside the room, hPa;
P - Atmosphere pressure at normal condition equal to 1013.25 hPa.
Without going deep into theory, we note that the quantity δ in depends to a small extent on temperature and can be considered with sufficient accuracy in practical calculations as a constant equal to 0.625 mg / (m * h * Pa).
Then, if the vapor permeability is known μ DIN easy to go to μ SNiP, i.e. μ SNiP = 0,625/ μ DIN
Above, we have already noted the importance of the issue of vapor permeability for multilayer structures. No less important, from the point of view of construction physics, is the question of the sequence of layers, in particular, the position of the insulation.
If we consider the probability of temperature distribution t, saturated steam pressure NS and pressure of unsaturated (real) steam Pp through the thickness of the enclosing structure, then from the point of view of the process of diffusion of water vapor, such a sequence of layers is most preferable, in which the resistance to heat transfer decreases, and the resistance to vapor permeation increases from the outside to the inside.
Violation of this condition, even without calculation, indicates the possibility of condensation falling out in the section of the enclosing structure (Fig. A1).
Rice. P1
Note that the arrangement of layers from various materials does not affect the value of the total thermal resistance, however, the diffusion of water vapor, the possibility and place of condensate fallout predetermine the location of the insulation on outer surface bearing wall.
Calculation of resistance to vapor permeability and verification of the possibility of condensate precipitation must be carried out in accordance with SNiP II-3-79 * "Construction heat engineering".
Recently, we had to face the fact that our designers are provided with calculations made according to foreign computer techniques. Let's express our point of view.
· Such calculations obviously have no legal force.
· Techniques are designed for higher winter temperatures... Thus, the German method "Bautherm" no longer works at temperatures below -20 ° C.
· Many important characteristics as initial conditions are not linked to our regulatory framework... So, the coefficient of thermal conductivity for heaters is given in a dry state, and according to SNiP II-3-79 * "Construction heat engineering" should be taken under conditions of sorption humidity for operation zones A and B.
· The balance of moisture gain and return is calculated for completely different climatic conditions.
Obviously, the number of winter months since negative temperatures for Germany and, say, for Siberia, they do not coincide at all.
1. Minimize selection interior space only insulation with the lowest thermal conductivity can be used
2. Unfortunately, the accumulating heat capacity of the array outer wall we are losing forever. But there is a payoff 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 junctions between the wall and the floor, the “cold bridges” can be removed if the insulation is applied partially to the floor slabs with the subsequent decoration of these junctions.
4. If you still believe in "wall breathing", please read THIS article. If not, then there is an obvious conclusion: thermal insulation material should be very tightly pressed against the wall. It is even better if the insulation becomes one piece with the wall. Those. there will be no gaps and crevices between the insulation and the wall. This prevents moisture from the room from reaching the dew point. The wall will always stay dry. Seasonal temperature fluctuations without moisture will not have negative impact on walls, which will increase their durability.
All these tasks can be solved only by sprayed polyurethane foam.
With the lowest thermal conductivity of all existing thermal insulation materials, polyurethane foam will take up a minimum of internal space.
The ability of polyurethane foam to reliably adhere to any surface makes it easy to apply to the ceiling to reduce "cold bridges".
When applied to walls, polyurethane foam, being in a liquid state for some time, fills all cracks and micro cavities. Foaming and polymerizing directly at the point of application, the polyurethane foam becomes one with the wall, blocking the access of destructive moisture.
Vapor permeability of walls
Supporters of the false concept of "healthy breathing of walls", in addition to sinning against the truth of physical laws and deliberately misleading designers, builders and consumers, proceeding from a mercantile impulse to sell their goods by any means, slander and slander insulating materials with low vapor permeability (polyurethane foam) or heat-insulating material is completely vapor-proof (foam glass).
The essence of this malicious innuendo 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 with moisture. In order to debunk this invention, let's take a closer look at the physical processes that will occur in the case of facing under the plaster layer or using inside the masonry, for example, such a material as foam glass, the vapor permeability of which is zero.
So, due to the thermal insulation and sealing properties inherent in foam glass, the outer layer of plaster or masonry will come to an equilibrium temperature and humidity state with the external atmosphere. Also, the inner layer of the masonry will come 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 daily temperature and humidity changes, as well as seasonal changes.
The behavior of the inner layer of the wall is especially interesting in this respect. In fact, the inner part of the wall will act as an inertial buffer, the role of which is to smooth out drastic changes humidity in the room. In the event of a sharp humidification of the room, the inner part of the wall will adsorb excess moisture contained in the air, preventing air humidity from reaching 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 at the same time, not allowing the air to "dry out" and becomes like a desert one.
As a favorable result such a system thermal insulation with the use of polyurethane foam harmonic of fluctuations in air humidity in the room is smoothed out and thus guarantees a stable value (with minor fluctuations) of humidity acceptable for a healthy microclimate. Physics this process well studied by the developed construction and architectural schools of the world and to achieve a similar effect when using fiber inorganic materials as a heater in closed systems insulation, it is strongly recommended to have a reliable vapor-permeable layer on inside insulation systems. So much for the "healthy breath of the walls"!
Often in construction articles there is an expression - vapor permeability concrete walls... It means the ability of the material to pass water vapor, in the popular way - "breathe". This parameter has great importance, since waste products are constantly formed in the living room, which must be constantly removed outside.
General information
If you do not create normal ventilation in the room, dampness will be created in it, which will lead to the appearance of mold and mildew. Their secretions can be harmful to our health.
On the other hand, vapor permeability affects the ability of a material to accumulate moisture in itself. This is also a bad indicator, since the more it can hold it in itself, the higher the likelihood of fungus, putrefactive manifestations, and destruction during freezing.
Water vapor permeability is denoted by the Latin letter μ and is measured in mg / (m * h * Pa). The value indicates the amount of water vapor that can pass through wall material on an area of 1 m 2 and with a thickness of 1 m in 1 hour, as well as the difference between external and internal pressure of 1 Pa.
High ability to conduct water vapor in:
- foam concrete;
- aerated concrete;
- perlite concrete;
- expanded clay concrete.
The table closes with heavy concrete.
Advice: if you need to make a technological channel in the foundation, it will help you diamond drilling holes in concrete.
Aerated concrete
- The use of the material as a building envelope makes it possible to avoid the accumulation of unnecessary moisture inside the walls and to preserve its heat-saving properties, which will prevent possible destruction.
- Any aerated concrete and foam concrete block has in its composition ≈ 60% air, due to which the vapor permeability of aerated concrete is recognized at a good level, the walls in this case can "breathe".
- Water vapor seeps freely through the material, but does not condense in it.
The vapor permeability of aerated concrete, as well as foam concrete, significantly exceeds heavy concrete - for the first 0.18-0.23, for the second - (0.11-0.26), for the third - 0.03 mg / m * h * Pa.
I would especially like to emphasize that the structure of the material provides it effective removal moisture in environment, so that even when the material freezes, it does not collapse - it is forced out through the open pores. Therefore, when preparing, you should take into account this feature and select the appropriate plasters, putties and paints.
The instruction strictly regulates that their vapor permeability parameters are not lower than the aerated concrete blocks used for construction.
Advice: do not forget that the vapor permeability parameters depend on the density of aerated concrete and may differ by half.
For example, if you use the D400, their coefficient is 0.23 mg / m h Pa, while for the D500 it is already lower - 0.20 mg / m h Pa. In the first case, the numbers indicate that the walls will have a higher "breathing" ability. So when picking finishing materials for walls made of aerated concrete D400, make sure that their vapor permeability coefficient is the same or higher.
Otherwise, this will lead to a deterioration in the removal of moisture from the walls, which will affect the decrease in the level of comfort in living in the house. It should also be noted that if you have applied for exterior decoration vapor-permeable paint for aerated concrete, and for the interior - impermeable materials, the vapor will simply accumulate inside the room, making it wet.
Expanded clay concrete
The vapor permeability of expanded clay concrete blocks depends on the amount of filler in its composition, namely expanded clay - foamed fired clay. In Europe, such products are called eco- or bioblocks.
Tip: if you can't cut the expanded clay block with a regular circle and a grinder, use a diamond one.
For example, cutting reinforced concrete with diamond wheels makes it possible to quickly solve the problem.
Polystyrene concrete
The material is another representative cellular concrete... The vapor permeability of polystyrene concrete is usually equated to wood. You can make it yourself.
Today, more attention is being paid not only to the thermal properties of wall structures, but also to the comfort of living in a building. In terms of thermal inertness and vapor permeability, polystyrene concrete resembles wood materials, and heat transfer resistance can be achieved by changing its thickness. Therefore, cast monolithic polystyrene concrete is usually used, which is cheaper than ready-made slabs.
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 building, improving their strength and characteristics. The vapor permeability of foam concrete and aerated concrete, as well as heavy concrete, is distinguished by its indicators, which must be taken into account when choosing finishing materials. The video in this article will help you find Additional information on this topic.
One of the most important indicators is vapor permeability. It characterizes the ability of cellular stones to retain or allow water vapor to pass through. GOST 12852.0-7 contains General requirements to a method for determining the vapor permeability coefficient of gas blocks.
What is vapor permeability
Inside and outside buildings, the temperature is always different. Accordingly, the pressure is not the same. As a result, moist air masses existing both on the other and on the other sides of the walls tend to move to a zone of lower pressure.
But since the room, as a rule, is drier than outside, moisture from the street penetrates into the micro-crevices of the building materials. Thus, the wall structures are filled with water, which can not only worsen the microclimate in the premises, but also adversely affect the enclosing walls - they will eventually collapse.
The appearance and accumulation of moisture in any walls is an extremely dangerous factor for health. So, as a result of this process, there is not only a decrease in the thermal protection of the structure, but also fungi, mold and other biological microorganisms appear.
Russian standards state that the vapor permeability index is determined by the ability of the material to resist the penetration of water vapor into it. The vapor permeability coefficient is calculated in mg / (m.h.Pa) and shows how much water will pass within 1 hour through 1m2 of a surface 1 m thick, with a pressure difference from one and the other part of the wall - 1 Pa.
Vapor permeability of aerated concrete
Aerated concrete consists of closed air pockets (up to 85% of the total volume). This significantly reduces the material's ability to absorb water molecules. Even penetrating inside, water vapor evaporates quickly enough, which has a positive effect on vapor permeability.
Thus, it can be stated: this indicator directly depends on density of aerated concrete - the lower the density, the higher the vapor permeability, and vice versa. Accordingly, the higher the grade of porous concrete, the lower its density, which means that this indicator is higher.
Therefore, to reduce vapor permeability in the production of cellular artificial stones:
Such preventive measures lead to the fact that the performance of aerated concrete different brands have excellent vapor permeability values, as shown in the table below:
Water vapor permeability and interior decoration
On the other hand, moisture in the room must also be removed. For this for use special materials absorbing water vapor inside buildings: plaster, paper wallpaper, wood, etc.
This does not mean that decorating the walls with oven-baked tiles, plastic or vinyl wallpaper it does not follow. And reliable sealing of window and doorways- a prerequisite for high-quality construction.
When performing internal finishing works it should be remembered that the vapor permeability of each finishing layer (putty, plaster, paint, wallpaper, etc.) must be higher than the same indicator of the cellular wall material.
The most powerful barrier to the penetration of moisture into the interior of the building is the application of a primer layer on the inside of the main walls.
But do not forget that in any case, in residential and industrial buildings should exist efficient system ventilation. Only in this case can we talk about normal humidity in the room.
Aerated concrete is excellent construction material... In addition to the fact that buildings constructed from it perfectly accumulate and retain heat, it is not too humid or dry in them. And all thanks to the good vapor permeability, which every developer should know about.
