Almost any advertising and information brochure or article describing the advantages of cotton insulation certainly mentions such a property as high vapor permeability - i.e. the ability to pass water vapor through. This property is closely related to the concept of “breathing walls”, around which heated debates and discussions on many pages regularly flare up on various construction forums and portals.

If we go to the official Russian (Ukrainian, Belarusian) website of any manufacturer of cotton insulation (ISOVER, ROCKWOOL, etc.), we will definitely find information about the high vapor permeability of the material, which ensures the “breathing” of the walls and a favorable microclimate in the room.

An interesting fact is that such information is completely absent from the English-language websites of the above-mentioned companies. Moreover, most of the information materials on these portals promote the idea of ​​​​creating completely airtight, airtight house structures. For example, consider the official website of the Isover company in the *com domain zone.

We bring to your attention the “golden rules of insulation” from the point of view of ISOVER.

1. Insulation performance
2. Good air tightness
3. Controlled ventilation
4. High-quality installation(Quality fitting)

Below we provide some translated quotes from this article:

“On average, a family of 4 people produces steam equal to 12 liters of water. Under no circumstances should this steam escape through the walls and roof! Only ventilation system, suitable specific house and the mode of living in it can prevent the appearance of dark spots inside the room, streams of water flowing down the walls, damage to coatings and, ultimately, to the entire building.”

“Ventilation cannot be carried out by breaking the tightness of walls, windows, frames, shutters. All this only leads to the penetration of polluted air into the room, which disrupts the quality of air exchange inside the house, harms the building structures, the operation of the chimney and ventilation shafts. Under no circumstances should so-called 'breathing walls' be used as a design solution for home ventilation."

Having familiarized ourselves with the English-language websites of most manufacturers of cotton insulation, we can find out that the high vapor permeability of the produced material is not mentioned as an advantage on any of them. Moreover, these sites completely lack information about vapor permeability as a property of insulation.

Thus, we can come to the conclusion that cultivating the myth of vapor permeability is a successful marketing ploy of the company’s representative offices in Russia and the CIS countries, used to discredit manufacturers of vapor-tight insulation - extruded polystyrene foam and foam glass.

However, despite the dissemination of such misleading information, manufacturers of cotton insulation on Russian websites post Constructive decisions on insulation of roofs and walls using vapor barriers, which makes their discussions about “breathable” structures devoid of common sense.

"WITH inside The roof must be provided with a vapor barrier layer. ISOVER recommends using ISOVER VS 80 or ISOVER VARIO membranes.

When installing a vapor barrier, it is necessary to maintain the integrity of the membrane, install it overlapping, and seal the joints with vapor-proof mounting tape. This will ensure the safety of the roof for many years.”

1. External skin
2. Waterproofing membrane
3. Metal or wooden frame
4. Thermal and sound insulation ISOVER
5. Vapor barrier ISOVER VARIO KM Duplex UV or ISOVER VS 80
6. Drywall (eg GYPROC)

"For guard thermal insulation material from vapor humidification internal air install a vapor barrier film on the inner “warm” side of the insulation. To protect the wall from blowing from the outside of the insulation, it is advisable to provide a windproof layer.”

Similar information can be heard directly from company representatives:

Ekaterina Kolotushkina, head of the Frame House Construction department, Saint-Gobain ISOVER company:

“I would like to note that the durability of the entire roof structure depends not only on the same indicator load-bearing elements, but is also determined by the service life of all materials used. To maintain this parameter when insulating the roof, it is necessary to use steam, hydro, and wind insulating membranes to protect the structure from steam from inside the room and moisture from outside.”

NATALIA CHUPYRA, head of the “Retail Products” department of the company “SAINT-GOBAIN IZOVER”, states approximately the same thing, “My Home” magazine.

“ISOVER recommends a roofing “pie” of the following design (layer-by-layer): roof covering, hydro-windproof membrane, counter-lattice, rafters with thermal insulation between them, vapor barrier membrane, interior finishing.”

Natalia also recognizes the importance of the ventilation system in the house:

“When insulating a house from the inside, many people neglect supply and exhaust ventilation. This is fundamentally wrong, because it provides the correct microclimate in the house. There is a certain air exchange rate that needs to be maintained in the room.”

As we see, the manufacturers of cotton insulation themselves and their representatives admit that the vapor barrier layer is a necessary component of almost any structure in which such thermal insulation is used. And this is not surprising, because the penetration of water molecules into a hygroscopic thermal insulation material leads to its wetting and, as a result, an increase in the thermal conductivity coefficient.

Thus, the high vapor permeability of insulation is more of a disadvantage than an advantage. Many manufacturers of vapor-tight thermal insulation have repeatedly tried to draw the attention of consumers to this fact, citing as arguments the opinions of scientists and qualified specialists in the field of construction.

For example, a well-known expert in the field of thermophysics, Doctor of Technical Sciences, Professor, K.F. Fokin states: “From a thermotechnical point of view, the air permeability of fences is more likely negative quality, since in winter time infiltration (air movement from inside to outside) causes additional heat loss from the fences and cooling of the premises, and exfiltration (air movement from outside to inside) can adversely affect the humidity regime of external fences, promoting moisture condensation.”

Wet insulation requires additional protection as waterproofing and vapor barrier membranes. Otherwise, the thermal insulation material ceases to fulfill its main task - to retain heat indoors. In addition, wet insulation becomes a favorable environment for the development of fungi, mold and other harmful microorganisms, which negatively affects the health of household members and also leads to the destruction of structures in which it is a part.

Thus, a high-quality thermal insulation material must have such undeniable advantages, such as low thermal conductivity, high strength, water resistance, environmental friendliness and safety for humans and environment, as well as low vapor permeability. The use of such thermal insulation material will not make the walls of your house “breathable”, but will allow them to fulfill their direct function - to maintain a favorable microclimate in the house and provide reliable protection from negative environmental factors.

IN Lately Various external insulation systems are increasingly used in construction: “wet” type; ventilated facades; modified well masonry, etc. What they all have in common is that they are multilayer enclosing structures. And for multilayer structures questions vapor permeability layers, moisture transfer, quantification falling condensate are issues 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 construction physics are the same and operate in the same way, for example, both in Russia and in Germany, but the approach methods and regulatory framework are very often very different.

Let us explain this using 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 a layer of air 1 m thick with the vapor permeability of a layer of material of the same thickness, we obtain the vapor permeability coefficient

μ DIN (dimensionless) = air vapor permeability/material vapor permeability

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 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. Obviously, the amount of water vapor passing through this layer will be less, the greater its thickness. If you multiply μ DIN And d, then we get the so-called air equivalent gap or diffuse 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 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 air vapor permeability.

SNiP II-3-79* "Construction Heat Engineering" determines vapor permeation resistance 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 issue of linking the 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 R0- gas constant of water vapor equal to 462 N*m/(kg*K);

T- indoor temperature, K;

p 0- average indoor air pressure, hPa;

P- atmospheric pressure at in good condition, equal to 1013.25 hPa.

Without going deeply into the 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 building physics, is the issue of the sequence of layers, in particular, the position of the insulation.

If we consider the probability of temperature distribution t, saturated vapor pressure Rn and unsaturated (real) vapor pressure Pp through the thickness of the enclosing structure, then from the point of view of the process of diffusion of water vapor, the most preferable sequence of layers is 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 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 overall thermal resistance, however, the diffusion of water vapor, the possibility and location of condensation predetermine the location of the insulation on outer surface load-bearing wall.

Calculation of vapor permeability resistance and checking the possibility of condensation loss must be carried out according to SNiP II-3-79* “Construction Heat Engineering”.

Recently we have had to deal with the fact that our designers are provided with calculations performed using foreign computer methods. Let's express our point of view.

· Such calculations obviously have no legal force.

· Methods are designed for higher winter temperatures. Thus, the German “Bautherm” method no longer works at temperatures below -20 °C.

· Many important characteristics as initial conditions are not linked to our regulatory framework. Thus, the thermal conductivity coefficient for insulation materials is given in a dry state, and according to SNiP II-3-79* “Building Heat Engineering” it should be taken under conditions of sorption humidity for operating zones A and B.

· The balance of moisture gain and loss is calculated for completely different climatic conditions.

It is obvious that the number of winter months from negative temperatures for Germany and, say, for Siberia are completely different.

Vapor permeability table- this is a complete summary table with data on the vapor permeability of all possible materials, used in construction. The word “vapor permeability” itself means the ability of layers of building material to either transmit or retain water vapor due to different pressure values ​​on both sides of the material at the same atmospheric pressure. This ability is also called the resistance coefficient and is determined by special values.

The higher the vapor permeability index, the more wall can contain moisture, which means that the material has low frost resistance.

Vapor permeability table indicates the following indicators:

1. Thermal conductivity is a kind of indicator of the energetic transfer of heat from more heated particles to less heated particles. Consequently, equilibrium is established in temperature conditions. If the apartment has high thermal conductivity, then this is the most comfortable conditions.
2. Thermal capacity. Using it, you can calculate the amount of heat supplied and heat contained in the room. It is imperative to bring it to a real volume. Thanks to this, temperature changes can be recorded.
3. Thermal absorption is the enclosing structural alignment during temperature fluctuations. In other words, thermal absorption is the degree to which wall surfaces absorb moisture.
4. Thermal stability is the ability to protect structures from sudden fluctuations in heat flow.

Completely all the comfort in the room will depend on these thermal conditions, which is why during construction it is so necessary vapor permeability table, as it helps to effectively compare different types of vapor permeability.

On the one hand, vapor permeability has a good effect on the microclimate, and on the other hand, it destroys the materials from which the house is built. In such cases, it is recommended to install a vapor barrier layer with outside Houses. After this, the insulation will not allow steam to pass through.

Vapor barriers are materials that are used from negative impact air vapor to protect the insulation.

There are three classes of vapor barrier. They differ in mechanical strength and resistance to vapor permeability. The first class of vapor barrier is rigid materials based on foil. The second class includes materials based on polypropylene or polyethylene. And the third class consists of soft materials.

Table of vapor permeability of materials.

Table of vapor permeability of materials- these are construction standards of international and domestic vapor permeability standards building materials.

Table of vapor permeability of materials.

Material	Vapor permeability coefficient, mg/(m*h*Pa)
Aluminum
Arbolit, 300 kg/m3
Arbolit, 600 kg/m3
Arbolit, 800 kg/m3
Asphalt concrete
Foamed synthetic rubber
Drywall
Granite, gneiss, basalt
Chipboard and fibreboard, 1000-800 kg/m3
Chipboard and fibreboard, 200 kg/m3
Chipboard and fibreboard, 400 kg/m3
Chipboard and fibreboard, 600 kg/m3
Oak along the grain
Oak across the grain
Reinforced concrete
Limestone, 1400 kg/m3
Limestone, 1600 kg/m3
Limestone, 1800 kg/m3
Limestone, 2000 kg/m3
Expanded clay (bulk, i.e. gravel), 200 kg/m3	0.26; 0.27 (SP)
Expanded clay (bulk, i.e. gravel), 250 kg/m3
Expanded clay (bulk, i.e. gravel), 300 kg/m3
Expanded clay (bulk, i.e. gravel), 350 kg/m3
Expanded clay (bulk, i.e. gravel), 400 kg/m3
Expanded clay (bulk, i.e. gravel), 450 kg/m3
Expanded clay (bulk, i.e. gravel), 500 kg/m3
Expanded clay (bulk, i.e. gravel), 600 kg/m3
Expanded clay (bulk, i.e. gravel), 800 kg/m3
Expanded clay concrete, density 1000 kg/m3
Expanded clay concrete, density 1800 kg/m3
Expanded clay concrete, density 500 kg/m3
Expanded clay concrete, density 800 kg/m3
Porcelain tiles
Clay brick, masonry
Hollow ceramic brick (1000 kg/m3 gross)
Hollow ceramic brick (1400 kg/m3 gross)
Brick, silicate, masonry
Large format ceramic block(warm ceramics)
Linoleum (PVC, i.e. unnatural)
Mineral wool, stone, 140-175 kg/m3
Mineral wool, stone, 180 kg/m3
Mineral wool, stone, 25-50 kg/m3
Mineral wool, stone, 40-60 kg/m3
Mineral wool, glass, 17-15 kg/m3
Mineral wool, glass, 20 kg/m3
Mineral wool, glass, 35-30 kg/m3
Mineral wool, glass, 60-45 kg/m3
Mineral wool, glass, 85-75 kg/m3
OSB (OSB-3, OSB-4)
Foam concrete and aerated concrete, density 1000 kg/m3
Foam concrete and aerated concrete, density 400 kg/m3
Foam concrete and aerated concrete, density 600 kg/m3
Foam concrete and aerated concrete, density 800 kg/m3
Expanded polystyrene (foam), plate, density from 10 to 38 kg/m3
Extruded polystyrene foam (EPS, XPS)	0.005 (SP); 0.013; 0.004
Expanded polystyrene, plate
Polyurethane foam, density 32 kg/m3
Polyurethane foam, density 40 kg/m3
Polyurethane foam, density 60 kg/m3
Polyurethane foam, density 80 kg/m3
Block foam glass	0 (rarely 0.02)
Bulk foam glass, density 200 kg/m3
Bulk foam glass, density 400 kg/m3
Glazed ceramic tiles
Clinker tiles	low; 0.018
Gypsum slabs (gypsum slabs), 1100 kg/m3
Gypsum slabs (gypsum slabs), 1350 kg/m3
Fiberboard and wood concrete slabs, 400 kg/m3
Fiberboard and wood concrete slabs, 500-450 kg/m3
Polyurea
Polyurethane mastic
Polyethylene
Lime-sand mortar with lime (or plaster)
Cement-sand-lime mortar (or plaster)
Cement-sand mortar (or plaster)
Ruberoid, glassine
Pine, spruce along the grain
Pine, spruce across the grain
Plywood
Cellulose ecowool

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 on this moment This is the most complete table.

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 the 25 most recent comments. Show all comments (63).

Vapor permeability - 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 a relative humidity of 55%, 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. in this case, it becomes necessary 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 construction 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 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, a well-known 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 such an unfavorable condition suddenly arises that 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:

Plasterboard 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 climatic 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 get sufficient quantity moisture for dew to occur.

To be fair, it must be said that ecowool cannot be installed without vapor barrier films! And if you add to " wall pie"vapor barrier film between OSB and ecowool on the inside of the room, then the condensation zone will practically come out of the insulation and the structure will fully meet the requirements for humidification (see picture on the left). However, the vapor barrier device practically makes no sense in thinking about the benefits of the "breathing" effect for the microclimate of the room walls." The vapor barrier membrane has a vapor permeability coefficient of about 0.1 mg/(m h Pa), and is sometimes used as a vapor barrier 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, layer interior decoration, 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.