Extruded or extruded polystyrene foam (EPS, EPPS, XPS), styrofoam (PSV / EPS) and polystyrene foam (PSB-S, expanded polystyrene, styropor) are widely used in Russia as thermal insulation material(insulation). Unfortunately, manufacturers often keep silent about the fact that due to the lack of vapor permeability, these materials can lead to the appearance of fungi and mold. This is especially true for non-vapor permeable extruded polystyrene foam, which for this reason is used to insulate brick and concrete walls Not recommended.
But recently I came across a premium cottage community near St. Petersburg, which used imported materials, including Belgian brick and Neopor polystyrene foam insulation. I was shocked that such houses were called eco-houses. Passive house when using 400 mm brickwork, as well as 350 mm of Neopor insulation on the walls, 300 mm of extruded polystyrene foam under the foundation slab, 400 mm of Neopor insulation on the floor slabs in a run-up - this is of course excellent. Moreover, a very small number of houses in Russia correspond to the German Passive House standard. But an eco-house...
In addition, the choice of polystyrene foam, albeit from the German manufacturer BASF, as insulation seemed strange. It is possible that this is the desire to do everything according to Western tracing paper and from Western materials. But it seems to me much more reasonable to use brick (foam glass chips) or.
It turned out that Neopor is a new generation of expanding polystyrene foam (EPS) from BASF. In the Russian-language brochures "Wall insulation Neopor (BASF)" and "Neopor. Expanding polystyrene (EPS). Innovative insulation AI.", unfortunately, there is information about vapor transparency of this material missing completely. The entire emphasis is on black graphite granules, which make it possible to reduce the thickness of the insulation by 15 percent, while maintaining the thermal conductivity coefficient.
Information about Neopor on the BASF website in Russian is generally scant. But in English you can find more interesting things. For example, the following:
Water and Neopor are good friends.Neopor Rigid Thermal Insulation is a closed-cell foam, but not all closed-cell foams are created equally. Neopor Rigid Thermal has a Class III Vapor Permeability rating of between 2.5 and 5.5 depending on thickness and density. This means walls constructed with Neopor as Continuous Insulation can more easily transport water vapor, reducing the likelihood of mold, mildew and structural damage. And, Neopor Rigid Thermal Insulation has low water absorption relative to traditional insulation materials.
I'll try to translate:
Water and Neopor are good friends.Neopor Solid Insulation Is Closed Cell Foam, But Not All closed cells made the same way. Neopor Rigid Thermal has class 3 vapor permeability in the range from 2.5 to 5.5, depending on thickness and density. This means that walls built using Neopor as continuous insulation can easily carry steam, reducing the likelihood of mold, false powdery mildew as well as structural damage. Neopor solid insulation has less water absorption than traditional insulation materials.
In Russian sources I came across information that the vapor permeability of Neopor is at least 0.05 mg / (m.h.Pa). But I'm not sure that this data can be trusted. Concrete has less vapor permeability. But brick has more, and it varies greatly depending on what kind of brick it is. So everything is correctly stated about reducing the likelihood of fungi and mold. If you use extruded polystyrene foam, styrofoam or polystyrene foam for insulation stone walls, then it is precisely this type that is vapor-permeable (i.e., extruded polystyrene foam immediately disappears). Although environmentally friendly, non-flammable and durable - foam glass chips and vermiculite - even with vapor permeability everything is much better. In any case, in addition to environmental friendliness, pay attention to the fact that the durability of the insulation corresponds to the durability of the walls of the house, and the vapor permeability of the insulation is at the level of the vapor permeability of the walls or higher.
Of course, the problem with insulation materials that do not release steam can be solved using forced ventilation, and also with the help interior decoration blocking the passage of steam. But whether it’s worth doing this is up to you to decide. Moreover, with such a struggle with the cause, there is always a chance that something will go wrong, including due to a mistake by the finishers or equipment breakdown.
In general, be careful when reading marketing brochures, even if it is in the premium segment. Beautiful pictures and imported materials are not a guarantee of quality and environmental friendliness. Of course, for 60 million rubles in the case of Wright Park, the cottage turns out to be very interesting solutions And quality materials. But for that kind of money, I would still avoid solutions like this one from the company Active House LLC.
Vapor permeability is the ability of a material to pass or retain steam as a result of the difference in the partial pressure of water vapor at the same atmospheric pressure on both sides of the material. Vapor permeability is characterized by the value of the coefficient of vapor permeability or the value of the coefficient of permeability resistance when exposed to water vapor. The vapor permeability coefficient is measured in mg/(m·h·Pa).
The air always contains some amount of water vapor, and warm air always contains more than cold air. At an internal air temperature of 20 °C and relative humidity 55% of the air contains 8 g of water vapor per 1 kg of dry air, which creates a partial pressure of 1238 Pa. At a temperature of –10°C and a relative humidity of 83%, the air contains about 1 g of steam per 1 kg of dry air, creating a partial pressure of 216 Pa. Due to the difference in partial pressures between the indoor and outdoor air through the wall, there is a constant diffusion of water vapor from the warm room to the outside. As a result, in real operating conditions, the material in structures is in a somewhat moistened state. The degree of material moisture depends on the temperature and humidity conditions outside and inside the fence. The change in the thermal conductivity coefficient of the material in operating structures is taken into account by the thermal conductivity coefficients λ(A) and λ(B), which depend on the humidity zone of the local climate and the humidity conditions of the room.
As a result of the diffusion of water vapor in the thickness of the structure, moist air moves from interior spaces. Passing through the vapor-permeable fencing structures, moisture evaporates out. But if outer surface If there is a layer of material on the wall that does not or does not allow water vapor to pass through, moisture begins to accumulate at the border of the vapor-tight layer, causing the structure to become damp. As a result, the thermal protection of a wet structure decreases sharply, and it begins to freeze. V in this case there is a need to install a vapor barrier layer on the warm side of the structure.
It seems that everything is relatively simple, but vapor permeability is often remembered only in the context of the “breathability” of walls. However, this is the cornerstone in choosing insulation! You need to approach it very, very carefully! There are often cases when a homeowner insulates a house based only on the thermal resistance indicator, for example, wooden house polystyrene foam. As a result, it gets rotting walls, mold in all corners and blames the “non-ecological” insulation for this. As for polystyrene foam, due to its low vapor permeability, you need to use it wisely and think very carefully about whether it is suitable for you. It is for this reason that cotton wool or any other porous insulation materials are often better suited for insulating walls outside. In addition, it is more difficult to make a mistake with cotton insulation. However, concrete or brick houses You can safely insulate it with foam plastic - in this case, the foam “breathes” better than the wall!
The table below shows materials from the TCP list, the vapor permeability indicator is the last column μ.
How to understand what vapor permeability is and why it is needed. Many have heard, and some actively use, the term “breathable walls” - so, such walls are called “breathable” because they are able to pass air and water vapor through themselves. Some materials (for example, expanded clay, wood, all cotton insulation) allow steam to pass through well, while others transmit steam very poorly (brick, polystyrene foam, concrete). Steam exhaled by a person, released when cooking or taking a bath, if there is no exhaust hood in the house, creates high humidity. A sign of this is the appearance of condensation on windows or on pipes with cold water. It is believed that if a wall has high vapor permeability, then it is easy to breathe in the house. In fact, this is not entirely true!
IN modern house, even if the walls are made of “breathable” material, 96% of the steam is removed from the premises through the hood and vents, and only 4% through the walls. If vinyl or non-woven wallpaper is glued to the walls, then the walls do not allow moisture to pass through. And if the walls are truly “breathable,” that is, without wallpaper or other vapor barriers, heat will blow out of the house in windy weather. The higher the vapor permeability of a structural material (foam concrete, aerated concrete and other warm concrete), the more moisture it can absorb, and as a result, it has lower frost resistance. Steam leaving the house through the wall turns into water at the “dew point”. The thermal conductivity of a damp gas block increases many times, that is, the house will be, to put it mildly, very cold. But the worst thing is that when the temperature drops at night, the dew point moves inside the wall, and the condensate in the wall freezes. When water freezes, it expands and partially destroys the structure of the material. Several hundred such cycles lead to complete destruction of the material. Therefore, the vapor permeability of building materials can serve you poorly.
About the harm of increased vapor permeability on the Internet, it goes from site to site. I will not present its contents on my website due to some disagreement with the authors, but I would like to voice selected points. For example, famous manufacturer mineral insulation, Isover company, on its English site outlined the “golden rules of insulation” ( What are the golden rules of insulation?) from 4 points:
Effective insulation. Use materials with high thermal resistance(low thermal conductivity). A self-evident point that does not require special comment.
Tightness. Good sealing is a necessary condition For effective system thermal insulation! Leaking thermal insulation, regardless of its thermal insulation coefficient, can increase energy consumption for heating a building by 7 to 11%. Therefore, the airtightness of the building should be considered at the design stage. And upon completion of work, check the building for leaks.
Controlled ventilation. It is ventilation that is tasked with removing excess moisture and steam. Ventilation should not and cannot be carried out by violating the tightness of the enclosing structures!
High-quality installation. I think there is no need to talk about this point either.
It is important to note that the Isover company does not produce any foam insulation; they deal exclusively with mineral wool insulation, i.e. products with the highest vapor permeability! This really makes you wonder: how is it possible, it seems that vapor permeability is necessary for moisture removal, but manufacturers recommend complete sealing!
The point here is a misunderstanding of this term. The vapor permeability of materials is not intended to remove moisture from the living space - vapor permeability is needed to remove moisture from the insulation! The fact is that any porous insulation is not essentially an insulation itself; it only creates a structure that holds the true insulation - air - in a closed volume and, if possible, motionless. If something like this suddenly happens unfavorable condition If the dew point is in the vapor-permeable insulation, then moisture will condense in it. This moisture in the insulation does not come from the room! The air itself always contains some amount of moisture, and it is this natural moisture that poses a threat to the insulation. To remove this moisture outside, it is necessary that after the insulation there are layers with no less vapor permeability.
On average, a family of four produces steam equal to 12 liters of water per day! This moisture from the indoor air should in no way get into the insulation! Where to put this moisture - this should not worry the insulation in any way - its task is only to insulate!
Example 1
Let's look at the above with an example. Let's take two walls frame house the same thickness and the same composition (from the inside to the outer layer), they will differ only in the type of insulation:
Drywall sheet (10mm) - OSB-3 (12mm) - Insulation (150mm) - OSB-3 (12mm) - ventilation gap (30mm) - wind protection - facade.
We will choose insulation with absolutely the same thermal conductivity - 0.043 W/(m °C), the main, tenfold difference between them is only in vapor permeability:
Expanded polystyrene PSB-S-25.
Density ρ= 12 kg/m³.
Vapor permeability coefficient μ= 0.035 mg/(m h Pa)
Coef. thermal conductivity in climate conditions B ( worst indicator) λ(B)= 0.043 W/(m °C).
Density ρ= 35 kg/m³.
Vapor permeability coefficient μ= 0.3 mg/(m h Pa)
Of course, I also use exactly the same calculation conditions: inside temperature +18°C, humidity 55%, outside temperature -10°C, humidity 84%.
I carried out the calculation in thermal calculator By clicking on the photo you will go directly to the calculation page:
As can be seen from the calculation, the thermal resistance of both walls is exactly the same (R = 3.89), and even their dew point is located almost equally in the thickness of the insulation, however, due to the high vapor permeability, moisture will condense in the wall with ecowool, greatly moistening the insulation. No matter how good dry ecowool is, damp ecowool retains heat many times worse. And if we assume that the temperature outside drops to -25°C, then the condensation zone will be almost 2/3 of the insulation. Such a wall does not meet the standards for protection against waterlogging! With expanded polystyrene, the situation is fundamentally different because the air in it is in closed cells; it simply has nowhere to collect enough moisture for dew to form.
To be fair, it must be said that ecowool cannot be installed without vapor barrier films! And if you add it to the "wall pie" vapor barrier film between OSB and ecowool with inside premises, then the condensation zone will practically leave the insulation and the structure will fully satisfy the requirements for humidification (see picture on the left). However, the vaporization device practically makes no sense in thinking about the benefits of the “wall breathing” effect for the microclimate of the room. A vapor barrier membrane has a vapor permeability coefficient of about 0.1 mg/(m h Pa), and sometimes they are vapor barriered with polyethylene films or insulation with a foil side - their vapor permeability coefficient tends to zero.
But low vapor permeability is also not always good! When insulating fairly well-vapor-permeable walls made of gas-foam concrete with extruded polystyrene foam without vapor barrier from the inside, mold will certainly settle in the house, the walls will be damp, and the air will not be fresh at all. And even regular ventilation will not be able to dry such a house! Let's simulate a situation opposite to the previous one!
Example 2
The wall this time will consist of the following elements:
Aerated concrete grade D500 (200mm) - Insulation (100mm) - ventilation gap (30mm) - wind protection - facade.
We will choose exactly the same insulation, and moreover, we will make the wall with exactly the same thermal resistance (R = 3.89).
As we see, with completely equal thermal characteristics we can get radically opposite results from insulation with the same materials!!! It should be noted that in the second example, both structures meet the standards for protection against waterlogging, despite the fact that the condensation zone falls into the gas silicate. This effect is due to the fact that the plane of maximum moisture falls into the polystyrene foam, and due to its low vapor permeability, moisture does not condense in it.
The issue of vapor permeability needs to be thoroughly understood even before you decide how and with what you will insulate your home!
Layered walls
In a modern house, the requirements for thermal insulation of walls are so high that a homogeneous wall can no longer meet them. Agree, given the requirement for thermal resistance R=3, make a homogeneous brick wall 135 cm thick is not an option! Modern walls- these are multilayer structures, where there are layers that act as thermal insulation, structural layers, a layer exterior finishing, a layer of interior finishing, layers of steam-hydro-wind insulation. Due to the varied characteristics of each layer, it is very important to position them correctly! The basic rule in the arrangement of layers of a wall structure is as follows:
The vapor permeability of the inner layer should be lower than the outer one, so that steam can freely escape beyond the walls of the house. With this solution, the “dew point” moves to outside load-bearing wall and does not destroy the walls of the building. To prevent condensation inside the building envelope, the resistance to heat transfer in the wall should decrease, and the resistance to vapor permeation should increase from the outside to the inside.
I think this needs to be illustrated for better understanding.
So I waited. I don’t know about you, but I’ve been wanting to experiment for a long time. Otherwise it’s all theory and theory. She didn't answer my questions. I mean thermal engineering calculation according to DBN. So I collected samples and decided to experiment with them. I'm interested in how the material will behave when exposed to steam.
Armed himself with whatever he could. Two steamers, pans with cold accumulators, a stopwatch and a pyrometer. Oh, yes... Another bucket of water for the fourth experiment with immersing samples. And off we went... :)
I summarized the results of the experiment on vapor permeability and inertia in a table.
In general, the experience went wrong. Despite the different thermal conductivity of the materials, the surface temperature of the samples in the first experiment with a vapor barrier layer was practically the same. I suspect that the steam from the steamer, which escaped, also heated the surface of the samples. As soon as I blew air on the samples, the temperature dropped by 1-2 degrees. Although, in principle, the dynamics of temperature growth remained the same. But I was more interested in this, because the very conditions of the experiment are far from real.
Which surprised me. This is Bethol. Second experiment without vapor barrier. This behavior of the insulation should not be considered a disadvantage. In my experience, Betol itself was a representative of vapor-permeable insulation. I think mineral wool insulation would behave the same way, but with faster dynamics.
Experience is very revealing. A sharp increase in temperature (large heat loss) due to vapor permeability and subsequent cooling of the material when water begins to evaporate from the surface. The insulation warmed up so much that it allowed it to release water in a vapor state and thus cool itself.
Gas block 420 kg/m3. He disappointed me. No! Not in terms of quality! He just clearly showed that he is selfish! 🙂 It’s better not to design with it multilayer walls. Due to its higher vapor permeability, it retained warm steam worse than a dense foam block. This suggests that if this material is used, the entire temperature and humidity shock will be absorbed by the vapor-permeable insulation. In general, take a denser, thicker gas block, and interior walls glue materials with low vapor permeability ( vinyl wallpapers, plastic lining, oil painting etc)...
How do you like the foam block with high density(representative of inertial materials)? Well, isn't this lovely? After all, he clearly showed us how inertial material behaves when heat accumulates. I would like to note that when I removed it from the steamer it was hot. Its temperature was clearly higher than Betol and Gas-Block. During the same exposure time, it was able to accumulate more heat, which led to a higher temperature of the material by 2-3 degrees.
Analyzing the table, I received many answers and became even more convinced that in our climate it is necessary to build inertial houses and you will definitely save on heating...
Sincerely, Alexander Terekhov.
Table of vapor permeability of building materials
I collected information on vapor permeability by combining several sources. The same sign with the same materials is circulating around the sites, but I expanded it and added modern meanings vapor permeability from the websites of building materials manufacturers. I also checked the values with data from the document “Code of Rules SP 50.13330.2012” (Appendix T), and added those that were not there. So this is the most complete table at the moment.
| Material | Vapor permeability coefficient, mg/(m*h*Pa) |
| Reinforced concrete | 0,03 |
| Concrete | 0,03 |
| Cement-sand mortar (or plaster) | 0,09 |
| Cement-sand-lime mortar (or plaster) | 0,098 |
| Lime-sand mortar with lime (or plaster) | 0,12 |
| Expanded clay concrete, density 1800 kg/m3 | 0,09 |
| Expanded clay concrete, density 1000 kg/m3 | 0,14 |
| Expanded clay concrete, density 800 kg/m3 | 0,19 |
| Expanded clay concrete, density 500 kg/m3 | 0,30 |
| Clay brick, masonry | 0,11 |
| Brick, silicate, masonry | 0,11 |
| Hollow ceramic brick (1400 kg/m3 gross) | 0,14 |
| Hollow ceramic brick (1000 kg/m3 gross) | 0,17 |
| Large format ceramic block(warm ceramics) | 0,14 |
| Foam concrete and aerated concrete, density 1000 kg/m3 | 0,11 |
| Foam concrete and aerated concrete, density 800 kg/m3 | 0,14 |
| Foam concrete and aerated concrete, density 600 kg/m3 | 0,17 |
| Foam concrete and aerated concrete, density 400 kg/m3 | 0,23 |
| Fiberboard and wood concrete slabs, 500-450 kg/m3 | 0.11 (SP) |
| Fiberboard and wood concrete slabs, 400 kg/m3 | 0.26 (SP) |
| Arbolit, 800 kg/m3 | 0,11 |
| Arbolit, 600 kg/m3 | 0,18 |
| Arbolit, 300 kg/m3 | 0,30 |
| Granite, gneiss, basalt | 0,008 |
| Marble | 0,008 |
| Limestone, 2000 kg/m3 | 0,06 |
| Limestone, 1800 kg/m3 | 0,075 |
| Limestone, 1600 kg/m3 | 0,09 |
| Limestone, 1400 kg/m3 | 0,11 |
| Pine, spruce across the grain | 0,06 |
| Pine, spruce along the grain | 0,32 |
| Oak across the grain | 0,05 |
| Oak along the grain | 0,30 |
| Plywood | 0,02 |
| Chipboard and fibreboard, 1000-800 kg/m3 | 0,12 |
| Chipboard and fibreboard, 600 kg/m3 | 0,13 |
| Chipboard and fibreboard, 400 kg/m3 | 0,19 |
| Chipboard and fibreboard, 200 kg/m3 | 0,24 |
| Tow | 0,49 |
| Drywall | 0,075 |
| Gypsum slabs (gypsum slabs), 1350 kg/m3 | 0,098 |
| Gypsum slabs (gypsum slabs), 1100 kg/m3 | 0,11 |
| Mineral wool, stone, 180 kg/m3 | 0,3 |
| Mineral wool, stone, 140-175 kg/m3 | 0,32 |
| Mineral wool, stone, 40-60 kg/m3 | 0,35 |
| Mineral wool, stone, 25-50 kg/m3 | 0,37 |
| Mineral wool, glass, 85-75 kg/m3 | 0,5 |
| Mineral wool, glass, 60-45 kg/m3 | 0,51 |
| Mineral wool, glass, 35-30 kg/m3 | 0,52 |
| Mineral wool, glass, 20 kg/m3 | 0,53 |
| Mineral wool, glass, 17-15 kg/m3 | 0,54 |
| Extruded polystyrene foam (EPS, XPS) | 0.005 (SP); 0.013; 0.004 (???) |
| Expanded polystyrene (foam), plate, density from 10 to 38 kg/m3 | 0.05 (SP) |
| Expanded polystyrene, plate | 0,023 (???) |
| Cellulose ecowool | 0,30; 0,67 |
| Polyurethane foam, density 80 kg/m3 | 0,05 |
| Polyurethane foam, density 60 kg/m3 | 0,05 |
| Polyurethane foam, density 40 kg/m3 | 0,05 |
| Polyurethane foam, density 32 kg/m3 | 0,05 |
| Expanded clay (bulk, i.e. gravel), 800 kg/m3 | 0,21 |
| Expanded clay (bulk, i.e. gravel), 600 kg/m3 | 0,23 |
| Expanded clay (bulk, i.e. gravel), 500 kg/m3 | 0,23 |
| Expanded clay (bulk, i.e. gravel), 450 kg/m3 | 0,235 |
| Expanded clay (bulk, i.e. gravel), 400 kg/m3 | 0,24 |
| Expanded clay (bulk, i.e. gravel), 350 kg/m3 | 0,245 |
| Expanded clay (bulk, i.e. gravel), 300 kg/m3 | 0,25 |
| Expanded clay (bulk, i.e. gravel), 250 kg/m3 | 0,26 |
| Expanded clay (bulk, i.e. gravel), 200 kg/m3 | 0.26; 0.27 (SP) |
| Sand | 0,17 |
| Bitumen | 0,008 |
| Polyurethane mastic | 0,00023 |
| Polyurea | 0,00023 |
| Foamed synthetic rubber | 0,003 |
| Ruberoid, glassine | 0 - 0,001 |
| Polyethylene | 0,00002 |
| Asphalt concrete | 0,008 |
| Linoleum (PVC, i.e. unnatural) | 0,002 |
| Steel | 0 |
| Aluminum | 0 |
| Copper | 0 |
| Glass | 0 |
| Block foam glass | 0 (rarely 0.02) |
| Bulk foam glass, density 400 kg/m3 | 0,02 |
| Bulk foam glass, density 200 kg/m3 | 0,03 |
| Glazed ceramic tiles | ≈ 0 (???) |
| Clinker tiles | low (???); 0.018 (???) |
| Porcelain tiles | low (???) |
| OSB (OSB-3, OSB-4) | 0,0033-0,0040 (???) |
It is difficult to find out and indicate in this table the vapor permeability of all types of materials; manufacturers have created a huge number of different plasters, finishing materials. And, unfortunately, many manufacturers do not indicate this on their products. important characteristic like vapor permeability.
For example, when determining the value for warm ceramics (item “Large-format ceramic block”), I studied almost all the websites of manufacturers of this type of brick, and only some of them listed vapor permeability in the characteristics of the stone.
Also different manufacturers different meanings vapor permeability. For example, for most foam glass blocks it is zero, but some manufacturers have the value “0 - 0.02”.
Showing 25 latest comments. Show all comments (63).
The concept of “breathing walls” is considered a positive characteristic of the materials from which they are made. But few people think about the reasons that allow this breathing. Materials that can pass both air and steam are vapor permeable.
A clear example of building materials with high vapor permeability:
- wood;
- expanded clay slabs;
- foam concrete.
Concrete or brick walls are less permeable to steam than wood or expanded clay.
Indoor steam sources
Human breathing, cooking, water vapor from the bathroom and many other sources of steam in the absence exhaust device create high level indoor humidity. You can often observe the formation of perspiration on window glass V winter time, or on cold water pipes. These are examples of water vapor forming inside a home.
What is vapor permeability
The design and construction rules give the following definition of the term: vapor permeability of materials is the ability to pass through droplets of moisture contained in the air due to different values of partial vapor pressures on opposite sides at identical values air pressure. It is also defined as the density of the steam flow passing through a certain thickness of the material.
The table with a vapor permeability coefficient compiled for building materials is conditional in nature, since the given calculated values humidity and atmospheric conditions do not always correspond to real conditions. The dew point can be calculated based on approximate data.
Wall design taking into account vapor permeability
Even if the walls are built from a material that has high vapor permeability, this cannot be a guarantee that it will not turn into water within the thickness of the wall. To prevent this from happening, you need to protect the material from the difference in partial vapor pressure from inside and outside. Protection against the formation of steam condensate is carried out using OSB boards, insulating materials such as penoplex and vapor-proof films or membranes that prevent steam from penetrating into the insulation.
The walls are insulated so that closer to the outer edge there is a layer of insulation that is unable to form moisture condensation and pushes back the dew point (water formation). In parallel with protective layers V roofing pie Proper ventilation gap must be ensured.
Destructive effects of steam
If the wall cake has a weak ability to absorb steam, it is not in danger of destruction due to the expansion of moisture from frost. The main condition is to prevent moisture from accumulating in the thickness of the wall, but to ensure its free passage and weathering. It is equally important to arrange forced exhaust excess moisture and steam from the room, connect a powerful ventilation system. By observing the above conditions, you can protect the walls from cracking and increase the service life of the entire house. Constant passage of moisture through Construction Materials accelerates their destruction.
Use of conductive qualities
Taking into account the peculiarities of building operation, the following insulation principle is applied: the most vapor-conducting insulating materials are located outside. Thanks to this arrangement of layers, the likelihood of water accumulating when the outside temperature drops is reduced. To prevent the walls from getting wet from the inside, the inner layer is insulated with a material that has low vapor permeability, for example, a thick layer of extruded polystyrene foam.
The opposite method of using the vapor-conducting effects of building materials has been successfully used. It consists of covering a brick wall with a vapor barrier layer of foam glass, which interrupts the moving flow of steam from the house to the street during low temperatures. The brick begins to accumulate moisture in the rooms, creating a pleasant indoor climate thanks to a reliable vapor barrier.
Compliance with the basic principle when constructing walls
Walls must have a minimum ability to conduct steam and heat, but at the same time be heat-intensive and heat-resistant. When using one type of material, the required effects cannot be achieved. The outer wall part must retain cold masses and prevent their impact on internal heat-intensive materials that maintain a comfortable thermal regime inside the room.
Ideal for inner layer reinforced concrete, its heat capacity, density and strength have maximum indicators. Concrete successfully smoothes out the difference between night and day temperature changes.
When conducting construction work make up wall pies taking into account the basic principle: the vapor permeability of each layer should increase in the direction from inner layers to the outside.
Rules for the location of vapor barrier layers
To ensure the best performance multilayer structures structures, the rule applies: on the side having more high temperature, materials with increased resistance to steam penetration and increased thermal conductivity are used. Layers located on the outside must have high vapor conductivity. For the normal functioning of the enclosing structure, it is necessary that the coefficient of the outer layer is five times higher than that of the layer located inside. 
When this rule is followed, water vapor trapped in warm layer walls, it will not be difficult to quickly exit through more porous materials.
If this condition is not met, the inner layers of building materials harden and become more thermally conductive.
Introduction to the table of vapor permeability of materials
When designing a house, the characteristics of building materials are taken into account. The Code of Rules contains a table with information about what coefficient of vapor permeability building materials have under normal conditions. atmospheric pressure and average air temperature.
Material | Vapor permeability coefficient |
extruded polystyrene foam | |
polyurethane foam | |
mineral wool | |
reinforced concrete, concrete | |
pine or spruce | |
expanded clay | |
foam concrete, aerated concrete | |
granite, marble | |
drywall | |
chipboard, osp, fibreboard | |
foam glass | |
roofing felt | |
polyethylene | |
linoleum |
The importance of the vapor permeability table of materials
The vapor permeability coefficient is important parameter, which is used to calculate the layer thickness insulation materials. The quality of insulation of the entire structure depends on the correctness of the results obtained.
Sergey Novozhilov - expert on roofing materials with 9 years experience practical work in area engineering solutions in construction.