1. Minimize selection internal space only insulation with the lowest thermal conductivity coefficient can
2. Unfortunately, the accumulating heat capacity of the array outer wall we lose forever. But there is a benefit here:
A) there is no need to waste energy resources on heating these walls
B) when you turn on even the smallest heater, the room will almost immediately become warm.
3. At the junction of the wall and the ceiling, “cold bridges” can be removed if the insulation is partially applied to the floor slabs and then decorated with these junctions.
4. If you still believe in the “breathing of walls,” then please read THIS article. If not, then the obvious conclusion is: the thermal insulation material must be pressed very tightly against the wall. It’s even better if the insulation becomes one with the wall. Those. there will be no gaps or cracks between the insulation and the wall. This way, moisture from the room will not be able to enter the dew point area. The wall will always remain dry. Seasonal temperature fluctuations without access to moisture will not have an impact negative influence on the walls, which will increase their durability.
All these problems can be solved only by sprayed polyurethane foam.
Having the lowest thermal conductivity coefficient of all existing thermal insulation materials, polyurethane foam will occupy a minimum of internal space.
The ability of polyurethane foam to reliably adhere to any surface makes it easy to apply it 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 microcavities. Foaming and polymerizing directly at the point of application, polyurethane foam becomes one with the wall, blocking access to destructive moisture.
VAPIROPER 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, based on a mercantile motive to sell their goods by any means, slander and slander thermal insulation materials with low vapor permeability (polyurethane foam) or The thermal insulation material is completely vapor-tight (foam glass).
The essence of this malicious insinuation 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 moisture. In order to debunk this fiction, let's take a closer look at the physical processes that will occur in the case of cladding under a plaster layer or using inside a masonry, for example, a material such as foam glass, the vapor permeability of which is zero.
So, due to the inherent thermal insulation and sealing properties of foam glass, the outer layer of plaster or masonry will come to an equilibrium temperature and humidity state with the outside atmosphere. Also, the inner layer of masonry will enter into a certain balance with the microclimate interior spaces. Processes of water diffusion, both in the outer layer of the wall and in the inner; will have the character of a harmonic function. This function will be determined, for the outer layer, by daily changes in temperature and humidity, as well as seasonal changes.
Particularly interesting in this regard is the behavior of the inner layer of the wall. Actually, inner part the walls will act as an inertial buffer, whose role is to smooth out sudden changes in humidity in the room. In the event of sudden humidification of the room, the inside of the wall will adsorb excess moisture contained in the air, preventing air humidity from reaching the maximum value. At the same time, in the absence of moisture release into the air in the room, the inside of the wall begins to dry out, preventing the air from “drying out” and becoming desert-like.
As a favorable result of such an insulation system using polyurethane foam, the harmonic fluctuations in air humidity in the room are smoothed out and thereby guarantee a stable value (with minor fluctuations) of humidity acceptable for a healthy microclimate. The physics of this process has been studied quite well by developed construction and architectural schools around the world, and to achieve a similar effect when using inorganic fiber materials as insulation in closed systems for insulation, it is strongly recommended to have a reliable vapor-permeable layer on inside insulation systems. So much for “healthy breathing of the walls”!
First, let’s refute the misconception - it is not the fabric that “breathes,” but our body. More precisely, the surface of the skin. Man is one of those animals whose body strives to maintain a constant body temperature, regardless of environmental conditions. One of the most important mechanisms of our thermoregulation is the sweat glands hidden in the skin. They are also part of the body's excretory system. The sweat they produce, evaporating from the surface of the skin, carries with it some of the excess heat. Therefore, when we are hot, we sweat to avoid overheating.
However, this mechanism has one serious drawback. Moisture, quickly evaporating from the surface of the skin, can cause hypothermia, which leads to colds. Of course, in Central Africa, where man has evolved as a species, such a situation is rather rare. But in regions with changeable and predominantly cool weather, a person constantly had and still has to supplement his natural thermoregulation mechanisms with various clothes.
The ability of clothing to “breathe” implies its minimal resistance to the removal of vapors from the surface of the skin and the “ability” to transport them to the front side of the material, where the moisture released by a person can evaporate without “stealing” the excess amount of heat. Thus, the “breathable” material from which the clothing is made helps the human body maintain optimal temperature body, avoiding overheating or hypothermia.
The “breathing” properties of modern fabrics are usually described in terms of two parameters - “vapor permeability” and “air permeability”. What is the difference between them and how does this affect their use in clothing for sports and active rest?
What is vapor permeability?
Vapor permeability is the ability of a material to transmit or retain water vapor. In the outdoor apparel and equipment industry important has a high ability of the material to water vapor transport. The higher it is, the better, because... This allows the user to avoid overheating and still remain dry.
All fabrics and insulation materials used today have a certain vapor permeability. However, in numerical terms it is presented only to describe the properties of membranes used in the production of clothing, and for a very small number not waterproof textile materials. Most often, vapor permeability is measured in g/m²/24 hours, i.e. the amount of water vapor that will pass through square meter material per day.
This parameter is indicated by the abbreviation MVTR (“moisture vapor transmission rate” or “speed of passage of water vapor”).
The higher the value, the greater the vapor permeability of the material.
How is vapor permeability measured?
MVTR numbers are obtained from laboratory tests based on various techniques. Due to the large number of variables affecting the operation of the membrane - individual metabolism, air pressure and humidity, area of material suitable for moisture transport, wind speed, etc., there is no single standardized research method for determining vapor permeability. Therefore, in order to be able to compare samples of fabrics and membranes with each other, manufacturers of materials and finished clothing use whole line techniques. Each of them separately describes the vapor permeability of a fabric or membrane in a certain range of conditions. Today, the following test methods are most often used:
"Japanese" "upright cup" test (JIS L 1099 A-1)
The test sample is stretched and sealed on top of a cup, inside of which a strong desiccant - calcium chloride (CaCl2) - is placed. The cup is placed on certain time into a thermohydrostat, which maintains an air temperature of 40°C and a humidity of 90%.
Depending on how the weight of the desiccant changes during the control time, MVTR is determined. The technique is well suited for determining vapor permeability not waterproof fabrics, because the test sample is not in direct contact with water.
"Japanese" inverted cup test (JIS L 1099 B-1)
The test sample is stretched and hermetically fixed over a vessel with water. Afterwards it is turned over and placed over a cup with a dry desiccant - calcium chloride. After the control time, the desiccant is weighed, resulting in the calculation of MVTR.
Test B-1 is the most popular, as it demonstrates the highest numbers among all methods that determine the rate of passage of water vapor. Most often, it is its results that are published on labels. The most “breathable” membranes have an MVTR value according to the B1 test greater than or equal to 20,000 g/m²/24h according to test B1. Fabrics with values of 10-15,000 can be classified as noticeably vapor permeable, at least under not very intense loads. Finally, for clothing that requires little movement, a vapor permeability of 5-10,000 g/m²/24h is often sufficient.
The JIS L 1099 B-1 test method fairly accurately illustrates the performance of the membrane in ideal conditions(when there is condensation on its surface and moisture is transported to a drier environment with a lower temperature).
Sweating plate test or RET (ISO - 11092)
Unlike tests that determine the rate of water vapor transport through a membrane, the RET technique examines how much the test sample resists passage of water vapor.
A sample of fabric or membrane is placed on top of a flat porous metal plate, under which a heating element is connected. The plate temperature is maintained at the surface temperature of human skin (about 35°C). Water evaporating from heating element, passes through the plate and the test sample. This leads to heat loss on the surface of the plate, the temperature of which must be maintained constant. Accordingly, the higher the level of energy consumption to maintain a constant plate temperature, the lower the resistance of the tested material to the passage of water vapor through it. This parameter is designated as RET (Resistance of Evaporation of a Textile - “material resistance to evaporation”). The lower the RET value, the higher the breathability of the membrane or other material being tested.
- RET 0-6 - extremely breathable;
RET 6-13 - highly breathable; RET 13-20 - breathable; RET over 20 - non-breathable.
Equipment for carrying out the ISO-11092 test. On the right is a chamber with a “sweating plate”. A computer is required to obtain and process results and control the test procedure © thermetrics.com
In the laboratory of the Hohenstein Institute, with which Gore-Tex collaborates, this technique is complemented by testing real clothing samples by people on a treadmill. In this case, the results of the sweat plate tests are adjusted according to the testers' comments.
Testing Gore-Tex clothing on the treadmill © goretex.com
The RET test clearly illustrates the performance of the membrane in real conditions, but is also the most expensive and time-consuming on the list. For this reason, not all active clothing manufacturing companies can afford it. At the same time, RET is today the main method for assessing the vapor permeability of membranes from the Gore-Tex company.
The RET technique generally correlates well with the results of the B-1 test. In other words, a membrane that shows good breathability in the RET test will show good breathability in the inverted cup test.
Unfortunately, none of the test methods can replace the others. Moreover, their results do not always correlate with each other. We saw that the process of determining the vapor permeability of materials in various methods has many differences, simulating different conditions work.
In addition, different membrane materials operate on different principles. For example, porous laminates ensure relatively free passage of water vapor through the microscopic pores present in their thickness, and non-porous membranes transport moisture to the front surface like a blotter - with the help of hydrophilic polymer chains in their structure. It is quite natural that one test can simulate the advantageous conditions for the operation of a non-porous membrane film, for example, when moisture is closely adjacent to its surface, and another - for a microporous one.
Taken together, all this means that there is practically no point in comparing materials with each other based on data obtained from different test methods. It also makes no sense to compare the vapor permeability of different membranes if the test method for at least one of them is unknown.
What is breathability?
Breathability- the ability of a material to pass air through itself under the influence of its pressure difference. When describing the properties of clothing, a synonym for this term is often used - “breathability”, i.e. how wind-resistant the material is.
In contrast to methods for assessing vapor permeability, relative uniformity reigns in this area. To assess air permeability, the so-called Fraser test is used, which determines how much air will pass through the material during a control time. Speed air flow according to test conditions is usually 30 mph, but may vary.
The unit of measurement is the cubic foot of air passing through the material in one minute. Denoted by the abbreviation CFM (cubic feet per minute).
The higher the value, the higher the air permeability (“blowability”) of the material. Thus, poreless membranes demonstrate absolute “windproofness” - 0 CFM. Test methods are most often defined by ASTM D737 or ISO 9237 standards, which, however, give identical results.
Exact CFM figures are published relatively rarely by textile and ready-to-wear manufacturers. Most often this parameter is used to characterize windproof properties in descriptions various materials, developed and used within the production of SoftShell clothing.
Recently, manufacturers have begun to “remember” air permeability much more often. The fact is that, along with the air flow, much more moisture evaporates from the surface of our skin, which reduces the risk of overheating and condensation accumulation under clothes. Thus, the Polartec Neoshell membrane has slightly greater air permeability than traditional porous membranes (0.5 CFM versus 0.1). Thanks to this, Polartec was able to achieve significant better work of its material in conditions of windy weather and rapid user movement. The higher the air pressure outside, the better Neoshell removes water vapor from the body due to greater air exchange. At the same time, the membrane continues to protect the user from wind cooling, blocking about 99% of the air flow. This turns out to be enough to withstand even stormy winds, and therefore Neoshell has even found itself in the production of single-layer assault tents (a striking example is the BASK Neoshell and Big Agnes Shield 2 tents).
But progress does not stand still. Today there are many offers of well-insulated mid-layers with partial breathability, which can also be used as an independent product. They use either fundamentally new insulation - like Polartec Alpha, or use synthetic volumetric insulation with a very low degree of fiber migration, which allows the use of less dense “breathable” fabrics. Thus, Sivera Gamayun jackets use ClimaShield Apex, while Patagonia NanoAir uses insulation under the FullRange™ trademark, which is produced by the Japanese company Toray under the original name 3DeFX+. Identical insulation is used in Mountain Force ski jackets and trousers as part of the “12 way stretch” technology and Kjus ski clothing. The relatively high breathability of the fabrics in which these insulations are enclosed makes it possible to create an insulating layer of clothing that will not interfere with the removal of evaporated moisture from the surface of the skin, helping the user to avoid both getting wet and overheating.
SoftShell clothing. Subsequently, other manufacturers created an impressive number of their analogues, which led to the widespread use of thin, relatively durable, “breathable” nylon in clothing and equipment for sports and outdoor activities.
The vapor permeability table of materials is building code domestic and, of course, international standards. In general, vapor permeability is a certain ability of fabric layers to actively transmit water vapor due to different pressure results with a uniform atmospheric indicator on both sides of the element.
The ability to transmit and retain water vapor under consideration is characterized by special values called the coefficient of resistance and vapor permeability.
At this point, it is better to focus your attention on the internationally established ISO standards. They determine the high-quality vapor permeability of dry and wet elements.
A large number of people believe that breathing is a good sign. However, it is not. Breathable elements are those structures that allow both air and vapor to pass through. Expanded clay, foam concrete and trees have increased vapor permeability. In some cases, bricks also have these indicators.
If a wall is endowed with high vapor permeability, this does not mean that breathing becomes easy. A large amount of moisture accumulates in the room, which results in low resistance to frost. Coming out through the walls, the vapor turns into ordinary water.
Most manufacturers do not take into account when calculating this indicator important factors, that is, they are being cunning. According to them, each material is thoroughly dried. Damp ones increase thermal conductivity five times, therefore, it will be quite cold in an apartment or other room.
The most terrible moment is the drop in night temperature conditions, leading to a shift in the dew point in the wall openings and further freezing of the condensate. Subsequently, the resulting frozen water begins to actively destroy surfaces.
Indicators
The table indicates the vapor permeability of materials:
- , which is an energetic type of heat transfer from highly heated particles to less heated ones. Thus, equilibrium in temperature regimes is achieved and appears. With high indoor thermal conductivity, you can live as comfortably as possible;
- Thermal capacity calculates the amount of heat supplied and contained. It must be brought to a real volume. This is how temperature change is considered;
- Thermal absorption is the enclosing structural alignment in temperature fluctuations, that is, the degree of absorption of moisture by wall surfaces;
- Thermal stability is a property that protects structures from sharp thermal oscillatory flows. Absolutely all full comfort in a room depends on the general thermal conditions. Thermal stability and capacity can be active in cases where the layers are made of materials with increased thermal absorption. Stability ensures the normalized state of structures.
Vapor permeability mechanisms
At low levels of relative humidity, moisture in the atmosphere is actively transported through existing pores in building components. They acquire appearance, similar to individual molecules of water vapor.
In cases where humidity begins to rise, the pores in the materials are filled with liquids, directing the working mechanisms to be downloaded into capillary suction. Vapor permeability begins to increase, lowering the resistance coefficients, as the humidity in the building material increases.
For internal structures in already heated buildings, dry-type vapor permeability indicators are used. In places where heating is variable or temporary, wet types are used building materials, intended for external designs.
Vapor permeability of materials, the table helps to effectively compare various types vapor permeability.
Equipment
In order to correctly determine vapor permeability indicators, specialists use specialized research equipment:
- Glass cups or vessels for research;
- Unique tools required for thickness measuring processes with high level accuracy;
- Analytical type balances with weighing error.
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 from 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).
Everyone knows that comfortable temperature regime, and, accordingly, a favorable microclimate in the house is ensured largely due to high-quality thermal insulation. Lately there has been a lot of debate about what ideal thermal insulation should be and what characteristics it should have.
There are a number of thermal insulation properties, the importance of which is beyond doubt: thermal conductivity, strength and environmental friendliness. It is quite obvious that effective thermal insulation must have a low thermal conductivity coefficient, be strong and durable, and not contain substances harmful to humans and environment.
However, there is one property of thermal insulation that raises a lot of questions - vapor permeability. Should insulation be permeable to water vapor? Low vapor permeability - is it an advantage or a disadvantage?
Points for and against"
Proponents of cotton insulation assure that high vapor permeability is a definite plus; vapor-permeable insulation will allow the walls of your home to “breathe”, which will create a favorable microclimate in the room even in the absence of any additional system ventilation.
Adherents of Penoplex and its analogues say: the insulation should work like a thermos, and not like a leaky “quilted jacket”. In their defense they give the following arguments:
1. Walls are not at all the “breathing organs” of the house. They perform a completely different function - they protect the house from environmental influences. Respiratory organs for the home are ventilation system, and also, partially, windows and doorways.
In many European countries supply and exhaust ventilation is installed without fail in any residential premises and is perceived as the same norm as centralized system heating in our country.
2. The penetration of water vapor through walls is a natural physical process. But at the same time, the amount of this penetrating steam in a residential area with normal operating conditions is so small that it can be ignored (from 0.2 to 3% * depending on the presence/absence of a ventilation system and its efficiency).
* Pogorzelski J.A., Kasperkiewicz K. Thermal protection of multi-panel houses and energy saving, planning topic NF-34/00, (typescript), ITB library.
Thus, we see that high vapor permeability cannot act as a cultivated advantage when choosing thermal insulation material. Now let's try to find out whether this property can be considered a disadvantage?
Why is high vapor permeability of insulation dangerous?
IN winter time years, with sub-zero temperature outside the home, the dew point (the conditions under which water vapor reaches saturation and condenses) should be in the insulation (extruded polystyrene foam is taken as an example).
Fig. 1 Dew point in EPS slabs in houses with insulation cladding
Fig. 2 Dew point in EPS slabs in frame-type houses
It turns out that if thermal insulation has high vapor permeability, then condensation can accumulate in it. Now let's find out why condensation in insulation is dangerous?
Firstly, When condensation forms in the insulation, it becomes damp. Accordingly, it decreases thermal insulation characteristics and, conversely, thermal conductivity increases. Thus, the insulation begins to perform the opposite function - remove heat from the room.
Well-known expert in the field of thermophysics, Doctor of Technical Sciences, Professor, K.F. Fokin concludes: “Hygienists view the breathability of enclosures as positive quality, providing natural ventilation premises. But from a thermal technical point of view, the air permeability of fences is more likely negative quality, since in winter, infiltration (air movement from inside to outside) causes additional heat loss by fences and cooling of rooms, and exfiltration (air movement from outside to inside) can adversely affect humidity conditions external fences, promoting moisture condensation.”
In addition, SP 23-02-2003 “Thermal protection of buildings” section No. 8 states that the air permeability of building envelopes for residential buildings should be no more than 0.5 kg/(m²∙h).
Secondly, due to wetting, the heat insulator becomes heavier. If we are dealing with cotton insulation, then it sags and cold bridges form. In addition, the load on bearing structures. After several cycles: frost - thaw, such insulation begins to deteriorate. To protect moisture-permeable insulation from getting wet, it is covered with special films. A paradox arises: the insulation breathes, but it requires protection with polyethylene or a special membrane, which negates all its “breathing”.
Neither polyethylene nor the membrane allow water molecules to pass into the insulation. From the school physics course it is known that air molecules (nitrogen, oxygen, carbon dioxide) larger than a water molecule. Accordingly, air is also unable to pass through such protective films. As a result, we get a room with breathable insulation, but covered with an airtight film - a kind of polyethylene greenhouse.
