Calculations and recalculations on the vapor permeability of windproof membranes. Vapor permeability of walls - getting rid of fiction Facade vapor-permeable materials
The vapor permeability of materials table is a building code of domestic and, of course, international standards. In general, vapor permeability is a certain ability of fabric layers to actively pass water vapor due to different pressure results with a uniform atmospheric index on both sides of the element.
The considered ability to pass, as well as retain water vapor, is characterized by special values \u200b\u200bcalled the coefficient of resistance and vapor permeability.
At the moment, it is better to focus your own attention on the internationally established ISO standards. They determine the qualitative vapor permeability of dry and wet elements.
A large number of people are committed to the fact 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 the wall is endowed with high vapor permeability, this does not mean that it becomes easy to breathe. A large amount of moisture is collected in the room, respectively, there is a low resistance to frost. Leaving through the walls, the vapors turn into ordinary water.
When calculating this indicator, most manufacturers do not take into account important factors, that is, they are cunning. According to them, each material is thoroughly dried. Damp ones increase thermal conductivity by five times, therefore, it will be quite cold in an apartment or other room.
The most terrible moment is the fall of night temperature regimes, leading to a shift in the dew point in wall openings and further freezing of condensate. Subsequently, the resulting frozen waters begin to actively destroy the surface.
Indicators
The vapor permeability of materials table indicates the existing indicators:
- , which is an energy type of heat transfer from highly heated particles to less heated ones. Thus, an equilibrium in temperature regimes is carried out and appears. With a high apartment thermal conductivity, you can live as comfortably as possible;
- Thermal capacity calculates the amount of supplied and stored heat. It must necessarily be brought to a real volume. This is how temperature change is considered;
- Thermal absorption is an 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-fledged comfort in the 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
Moisture located in the atmosphere, at a low level of relative humidity, is actively transported through the existing pores in building components. They take on an appearance similar to individual water vapor molecules.
In those cases when the humidity begins to rise, the pores in the materials are filled with liquids, directing the working mechanisms for downloading into capillary suction. Vapor permeability begins to increase, lowering the resistance coefficients, with an increase in humidity in the building material.
For internal structures in already heated buildings, dry-type vapor permeability indicators are used. In places where heating is variable or temporary, wet types of building materials are used, intended for the outdoor version of structures.
Vapor permeability of materials, the table helps to effectively compare the various types of vapor permeability.
Equipment
In order to correctly determine the vapor permeability indicators, experts use specialized research equipment:
- Glass cups or vessels for research;
- Unique tools required for measuring thickness processes with a high level of accuracy;
- Analytical balance with weighing error.
During the construction process, any material should first of all be evaluated according to its operational and technical characteristics. When solving the problem of building a “breathing” house, which is most characteristic of buildings made of brick or wood, or vice versa, to achieve maximum resistance to vapor permeability, it is necessary to know and be able to operate with tabular constants to obtain calculated indicators of vapor permeability of building materials.
What is the vapor permeability of materials
Vapor permeability of materials- the ability to pass or retain water vapor as a result of the difference in the partial pressure of water vapor on both sides of the material at the same atmospheric pressure. Vapor permeability is characterized by a vapor permeability coefficient or vapor permeability resistance and is normalized by SNiP II-3-79 (1998) "Construction heating engineering", namely chapter 6 "Vapor permeability resistance of enclosing structures"
Table of vapor permeability of building materials
The vapor permeability table is presented in SNiP II-3-79 (1998) "Construction heat engineering", Appendix 3 "Thermal performance of building materials for structures". The vapor permeability and thermal conductivity of the most common materials used for the construction and insulation of buildings are presented in the table below.
Material | Density, kg/m3 | Thermal conductivity, W / (m * C) | Vapor permeability, Mg/(m*h*Pa) |
Aluminum | |||
asphalt concrete | |||
Drywall | |||
Chipboard, OSB | |||
Oak along the grain | |||
Oak across the grain | |||
Reinforced concrete | |||
Facing cardboard | |||
Expanded clay | |||
Expanded clay | |||
Expanded clay concrete | |||
Expanded clay concrete | |||
Brick ceramic hollow (gross 1000) | |||
Brick ceramic hollow (gross 1400) | |||
Red clay brick | |||
Brick, silicate | |||
Linoleum | |||
mineral wool | |||
mineral wool | |||
foam concrete | |||
foam concrete | |||
PVC foam | |||
Styrofoam | |||
Styrofoam | |||
Styrofoam | |||
EXTRUDED POLYSTYRENE FOAM | |||
POLYURETHANE FOAM | |||
POLYURETHANE FOAM | |||
POLYURETHANE FOAM | |||
POLYURETHANE FOAM | |||
Foam glass | |||
Foam glass | |||
Sand | |||
POLYUREA | |||
POLYURETHANE MASTIC | |||
Polyethylene | |||
Ruberoid, glassine | |||
Pine, spruce along the grain | |||
Pine, spruce across the grain | |||
Plywood |
Table of vapor permeability of building materials
The term "vapor permeability" itself indicates the property of materials to pass or retain water vapor in its thickness. The table of vapor permeability of materials is conditional, since the calculated values of the level of humidity and atmospheric action do not always correspond to reality. The dew point can be calculated according to the average value.
Each material has its own percentage of vapor permeability
Determining the level of steam permeability
In the arsenal of professional builders there are special technical tools that allow diagnosing the vapor permeability of a particular building material with high accuracy. To calculate the parameter, the following tools are used:
- devices that make it possible to accurately determine the thickness of the layer of building material;
- laboratory glassware for research;
- scales with the most accurate readings.
In this video you will learn about vapor permeability:
With the help of such tools, it is possible to correctly determine the desired characteristic. Since the experimental data are recorded in the tables of the vapor permeability of building materials, it is not necessary to establish the vapor permeability of building materials during the preparation of a dwelling plan.
Creation of comfortable conditions
To create a favorable microclimate in a dwelling, it is necessary to take into account the characteristics of the building materials used. Particular emphasis should be placed on vapor permeability. With knowledge of this ability of the material, it is possible to correctly select the raw materials necessary for housing construction. Data is taken from building codes and regulations, for example:
- vapor permeability of concrete: 0.03 mg/(m*h*Pa);
- vapor permeability of fiberboard, chipboard: 0.12-0.24 mg / (m * h * Pa);
- vapor permeability of plywood: 0.02 mg/(m*h*Pa);
- ceramic brick: 0.14-0.17 mg / (m * h * Pa);
- silicate brick: 0.11 mg / (m * h * Pa);
- roofing material: 0-0.001 mg / (m * h * Pa).
Steam generation in a residential building can be caused by human and animal breathing, food preparation, temperature differences in the bathroom, and other factors. No exhaust ventilation also creates a high degree of humidity in the room. In winter, it is often possible to notice the occurrence of condensate on windows and on cold pipelines. This is a clear example of the appearance of steam in residential buildings.
Protection of materials in the construction of walls
Building materials with high permeability steam cannot fully guarantee the absence of condensation inside the walls. In order to prevent the accumulation of water in the depths of the walls, the pressure difference of one of the components of the mixture of gaseous elements of water vapor on both sides of the building material should be avoided.
Provide protection from the appearance of liquid actually, using oriented strand boards (OSB), insulating materials such as foam and vapor barrier film or a membrane that prevents steam from seeping into the thermal insulation. Simultaneously with the protective layer, it is required to organize the correct air gap for ventilation.
If the wall cake does not have sufficient capacity to absorb steam, it does not risk being destroyed as a result of the expansion of condensate from low temperatures. The main requirement is to prevent the accumulation of moisture inside the walls and provide its unhindered movement and weathering.
An important condition is the installation of a ventilation system with forced exhaust, which will not allow excess liquid and steam to accumulate in the room. By fulfilling the requirements, you can protect the walls from cracking and increase the durability of the home as a whole.
Location of thermal insulation layers
To ensure the best performance of the multi-layer structure of the structure, the following rule is used: the side with a higher temperature is provided with materials with increased resistance to steam infiltration with a high coefficient of thermal conductivity.
The outer layer must have high vapor conductivity. For the normal operation of the enclosing structure, it is necessary that the index of the outer layer is five times higher than the values of the inner layer. Subject to this rule, water vapor that has entered the warm layer of the wall will leave it without much effort through more cellular building materials. Neglecting these conditions, the inner layer of building materials becomes damp, and its thermal conductivity becomes higher.
The selection of finishes also plays an important role in the final stages of construction work. Properly selected composition of the material guarantees effective removal of liquid into the external environment, therefore, even at sub-zero temperatures, the material will not collapse.
The vapor permeability index is a key indicator when calculating the size of the cross section of the insulation layer. The reliability of the calculations made will depend on how high-quality the insulation of the entire building will turn out.
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 capable of passing both air and steam are vapor-permeable.
A good 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.
Sources of steam indoors
Human breathing, cooking, water vapor from the bathroom and many other sources of steam in the absence of an exhaust device create a high level of humidity indoors. You can often observe the formation of perspiration on window panes in winter, or on cold water pipes. These are examples of the formation of water vapor inside the house.
What is vapor permeability
The design and construction rules give the following definition of the term: the vapor permeability of materials is the ability to pass through moisture droplets contained in the air due to different partial vapor pressures from opposite sides at the same air pressure values. It is also defined as the density of the steam flow passing through a certain thickness of the material.
The table, which has a vapor permeability coefficient, compiled for building materials, is conditional, since the specified calculated values \u200b\u200bof humidity and atmospheric conditions do not always correspond to real conditions. The dew point can be calculated based on approximate data.
Wall construction taking into account vapor permeability
Even if the walls are built from a material with high vapor permeability, this cannot be a guarantee that it will not turn into water in the thickness of the wall. To prevent this from happening, it is necessary 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 foam and vapor-tight films or membranes that prevent steam from penetrating into the insulation.
The walls are insulated in such a way that a layer of insulation is located closer to the outer edge, incapable of forming moisture condensation, pushing the dew point (water formation) away. In parallel with the protective layers in the roofing cake, it is necessary to ensure the correct ventilation gap.
The destructive action 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 the accumulation of moisture in the thickness of the wall, but to ensure its free passage and weathering. It is equally important to arrange a forced extraction of excess moisture and steam from the room, to connect a powerful ventilation system. By observing the above conditions, you can protect the walls from cracking, and increase the life of the whole house. The constant passage of moisture through building materials accelerates their destruction.
Use of conductive qualities
Taking into account the peculiarities of the operation of buildings, the following principle of insulation is applied: the most steam-conducting insulation materials are located outside. Due to this arrangement of layers, the likelihood of water accumulation when the temperature drops outside is reduced. To prevent the walls from getting wet from the inside, the inner layer is insulated with a material having low vapor permeability, for example, a thick layer of extruded polystyrene foam.
The opposite method of using the steam-conducting effects of building materials is successfully applied. It consists in the fact that a brick wall is covered 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 humidity in the rooms, creating a pleasant indoor climate thanks to a reliable vapor barrier.
Compliance with the basic principle when building walls
Walls should be characterized by a minimum ability to conduct steam and heat, but at the same time be heat-retaining and heat-resistant. When using one type of material, the desired effects cannot be achieved. The outer wall part is obliged to retain cold masses and prevent their impact on internal heat-intensive materials that maintain a comfortable thermal regime inside the room.
Reinforced concrete is ideal for the inner layer, its heat capacity, density and strength have maximum performance. Concrete successfully smooths out the difference between night and day temperature changes.
When carrying out construction work, wall cakes are made taking into account the basic principle: the vapor permeability of each layer should increase in the direction from the inner layers to the outer ones.
Rules for the location of vapor barrier layers
To ensure the best performance of multilayer structures of buildings, the rule is applied: on the side with a higher temperature, materials with increased resistance to steam penetration with increased thermal conductivity are placed. The layers located outside must have a high vapor conductivity. For the normal functioning of the building envelope, it is necessary that the coefficient of the outer layer is five times higher than the indicator of the layer located inside. 
When this rule is followed, it will not be difficult for water vapor that has entered the warm layer of the wall to quickly escape through more porous materials.
If this condition is not observed, the inner layers of building materials lock up and become more heat-conducting.
Familiarity with the table of vapor permeability of materials
When designing a house, the characteristics of building materials are taken into account. The Code of Practice contains a table with information on what vapor permeability coefficient building materials have under conditions of normal 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, OSB, fiberboard | |
foam glass | |
ruberoid | |
polyethylene | |
linoleum |
The importance of the material vapor permeability table
The vapor permeability coefficient is an important parameter that is used to calculate the thickness of the layer of insulation materials. The quality of the insulation of the entire structure depends on the correctness of the results obtained.
Sergey Novozhilov is an expert in roofing materials with 9 years of practical experience in the field of engineering solutions in construction.
Table of vapor permeability of building materials
I collected information on vapor permeability by linking several sources. The same plate with the same materials walks around the sites, but I expanded it, added modern vapor permeability values from the sites of building materials manufacturers. I also checked the values with the data from the document "Code of Rules SP 50.13330.2012" (Appendix T), added those that were not there. So at the 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 ceramic) | 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 fiberboard, 1000-800 kg/m3 | 0,12 |
| Chipboard and fiberboard, 600 kg/m3 | 0,13 |
| Chipboard and fiberboard, 400 kg/m3 | 0,19 |
| Chipboard and fiberboard, 200 kg/m3 | 0,24 |
| Tow | 0,49 |
| Drywall | 0,075 |
| Gypsum slabs (gypsum boards), 1350 kg/m3 | 0,098 |
| Gypsum slabs (gypsum boards), 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 |
| Expanded polystyrene extruded (EPPS, XPS) | 0.005 (SP); 0.013; 0.004 (???) |
| Expanded polystyrene (foam plastic), plate, density from 10 to 38 kg/m3 | 0.05 (SP) |
| Styrofoam, plate | 0,023 (???) |
| Ecowool cellulose | 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. not natural) | 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 tile (tile) | ≈ 0 (???) |
| Clinker tiles | low (???); 0.018 (???) |
| Porcelain stoneware | 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 variety of plasters and finishing materials. And, unfortunately, many manufacturers do not indicate such an important characteristic as vapor permeability on their products.
For example, when determining the value for warm ceramics (position "Large-format ceramic block"), I studied almost all the websites of manufacturers of this type of brick, and only some of them had vapor permeability indicated in the characteristics of the stone.
Also, different manufacturers have different vapor permeability values. For example, for most foam glass blocks it is zero, but for some manufacturers the value is "0 - 0.02".
The 25 most recent comments are shown. Show all comments (63).