How to calculate the dew point of aerated concrete. Choosing the best option for insulating aerated concrete walls
Did you build or buy own house. Or you are just about to do it, planning your actions in advance. We weighed all the pros and cons and came to the conclusion that the building should be made of stone, and the walls should be built from warm and effective material: aerated concrete. It is also cellular concrete, gas silicate, foam concrete. Is there a need to insulate walls made of aerated concrete (“thermal fur coat”), and if so, how to do it correctly?
Video report on the thermal insulation of a house made of aerated concrete with ecowool
Reasons for insulation
It seems obvious: to keep the house warmer and lower heating costs. But you can just increase the thickness of the walls? Hard mineral wool, most suitable for insulating facades, with a slab thickness of 100 mm will cost (in the central regions of the country) an average of 450 rubles per m 2. In terms of thermal characteristics, this is analogous cellular concrete 300 mm thick. And it will cost 900 rubles. In fact, if you count the entire structure of external insulation: mineral wool boards, two layers of glue, fasteners, plaster, mesh, the price will rise to 800 rubles per meter and will practically be equal to the cost of increasing the heat-insulating properties of the wall by increasing the thickness of the masonry. However, under a thicker wall you will have to build a more powerful and expensive foundation. “Thermal fur coat” still turns out to be more profitable. The most rational option in terms of price/energy saving ratio for middle zone Russia - a foundation 300 mm thick (preferably also insulated); walls made of aerated concrete 400 mm; insulation 100 mm.
The optimal insulation option: “thermal fur coat” using hard mineral wool slabs 100 mm thick
There is one more important point: Durability and the notorious dew point. Our continental climate is unfriendly to stone building materials. Moisture, getting into the internal pores of aerated concrete, freezes in cold weather, expands and gradually tears apart the walls. This applies not only to cellular concrete, but also to brick and concrete. In our area stone house will never last as long as, for example, in Southern Europe. If the Parthenon had been built in Moscow, it would have long ago fallen apart into separate pebbles. External insulation will again help to extend the life of the building in order to pass it on to great-grandchildren intact.
In heating engineering there is such a concept: “dew point”. This place is deep wall material with zero temperature. It is in this zone that the maximum amount of moisture condenses and the material either freezes or thaws again. Dry blocks look and feel like they have an average moisture content of 5-8%. During the thawing-freezing process, this water little by little but inexorably wears away the stone of our walls. What's the solution?
Aerated concrete is hydrophobic (absorbs moisture) and it is not worth leaving a residential building unplastered for the winter, it will be damp
Remove the dew point from the wall, move it outward. That is, make sure that aerated concrete is constantly in the positive temperature zone, then it will last significantly longer. Moreover, when correct design the wall will always be dry, which will create a healthy microclimate in the house. The fact that the dew point will completely shift into the insulation is not a problem. Firstly, it is an order of magnitude less susceptible to the destructive forces of freezing water. Secondly, unlike a main wall, insulation is easy to reconstruct.
Choose a method: outside or inside
We have already mentioned that the house should be insulated from the outside. But doing it from the inside is cheaper, easier and faster? Yes, but not so. Yes, there is no need to install scaffolding. Yes, you can use cheap soft glass wool and cover the walls with plasterboard, immediately completing the interior finishing. Yes, you can work under a roof in winter and in bad weather.
Alas, by doing insulation from the inside, we lose a lot. Firstly, we shift the “dew point” not outward, but, on the contrary, inside the wall. Thus, we only worsen the operating conditions of aerated concrete and reduce the durability of the building. Secondly, almost every building has so-called “cold bridges”. “Warm” walls made of cellular blocks also have “cold” elements: floor slabs, reinforced belts, lintels. They are more thermally conductive and through them cold penetrates into the house, and money evaporates from the house. Insulating aerated concrete walls from the outside solves this problem. The house, like a fur coat, is completely enclosed in a heat-insulated shell. The internal insulation is like a gill caftan with holes: the belly is warm, but the back is cold.
Let's summarize: internal insulation only partially solves the problem, the only correct option is external. It makes sense to insulate it from the inside if there is simply no other way out. For example, for some reason it is not possible to change appearance facade.
Rigid mineral wool slabs are used for external insulation.
What material is better to use
The eternal question of all developers: mineral wool or polystyrene foam? Mineral wool is more expensive, but better. Polystyrene foam is cheaper, but worse. It’s like crayfish on Privoz: large ones cost five rubles, small ones cost three rubles. Let’s try to figure out why mineral wool is better and whether it’s worth overpaying for it:
- Mineral wool and expanded polystyrene are extremely similar in thermal characteristics. The latter is even a little more effective. Mechanical properties and durability are also not much different.
- Mice hate mineral wool and love polystyrene foam. If anywhere on the surface polystyrene foam boards there will be no decoration, and the Mickey Mouse family will immediately make a cozy hole there. But, if the facade is completely covered with plaster, this will not happen.
- It is much easier to work with polystyrene foam, it is easier to cut, and random cracks can be easily eliminated with construction foam. Mineral wool boards are a little more difficult to process and you will have to work with protective gloves, goggles and preferably a respirator.
Polystyrene foam is cheaper than mineral wool
- Mineral wool is an absolutely fireproof material. Expanded polystyrene does not support a flame; it cannot be set on fire. However, when exposed to fire, it releases poisonous gases, similar to those that the Germans used during the First Imperialist War. In fact, if you don’t light fires along the facade and don’t pour gasoline on the walls, there won’t be any problems.
- But in terms of vapor permeability, the materials differ radically. And this is important. Aerated concrete has optimal vapor permeability. Inside a residential building, a rather a large number of moisture. Cooking in the kitchen, washing machine, home flowers, wet cleaning. And people themselves give off moisture through their skin and breath. Aerated concrete is able to absorb this moisture and remove it through the pores of the material to the outside. The vector of vapor movement is always directed from the inside to the street. This phenomenon is called the “breathing” of the wall and it has a beneficial effect on the microclimate. By the way, cellular concrete is second only to wood in terms of vapor permeability and is considered one of the friendliest for humans building materials.
Mineral wool fully supports beneficial features aerated concrete. Being even more vapor-permeable, it does not prevent the walls from “breathing”. Polystyrene foam practically does not allow vapor to pass through. The house, insulated with polystyrene foam, is tightly packed, like a “stuff” in a plastic bag. Of course, you can ventilate the rooms by simply opening the window. Of course, on average, only 8% of moisture escapes through the walls in a “normal” house; the rest is removed by ventilation. However, the humidity of walls insulated with foam plastic still increases by 4-8%. Albeit insignificantly, but because of this, the thermal characteristics of aerated concrete are reduced and the housing microclimate worsens.
Mineral wool is preferable for insulation aerated concrete walls
Undoubtedly, mineral wool has a significant advantage and is the best material for external wall insulation. Undoubtedly, polystyrene foam is radically cheaper and also serves good insulation. Conclusion: if your budget allows, it is better to use mineral wool. If “finance sings romances,” you can insulate the house with polystyrene foam.
What should be the thickness of the insulation?
We often see how people insulate their houses with thin slabs of 4, 3 and even 2 centimeters. This is a big mistake. Even the use of the most common 5-centimeter slabs is not very justified.
The thicker the insulation layer, the warmer the house will be and the lower the cost of gas or firewood. Everyone understands this. But it is not clear to everyone that by reducing the thickness of the insulation by as much as 40% (from 5 to 3 cm), the total savings on the structure will be only a ridiculous 10%. After all, the cost of glue, plaster, mesh, fasteners and labor almost does not depend on the thickness of the insulation and cannot be significantly reduced. That is why there is nothing stupider than investing in related materials and saving on the main thing - the thickness of the insulation. The optimal, economically justified insulation of aerated concrete walls for the central regions of Russia is a 10 cm slab. It makes no sense at all to use material less than 5 cm thick.
“Wet” and “dry” insulation
We won’t go into detail existing methods insulation. Manufacturers develop complex technologies and create clear, very detailed and well-illustrated manuals to help performers. They can be obtained from material sellers or downloaded online from original sites. Let us only mention that the instructions are written for a reason, and the technology must be followed strictly. Also, do not attempt to replace any materials from complex systems to cheaper ones. For example, it happens that instead of special adhesive and plaster compositions The cheapest tile adhesive is used for insulation. Yes, it will stick the slabs, but the service life and vapor permeability will be significantly lower than that of the “correct” composition.
- "Wet" system is lightweight
In fact, with the so-called “wet” technology, the facade remains completely dry. The insulation is fixed to the wall with glue and dowels with a large head. Then two thin leveling layers of plaster are applied, and a reinforcing layer is placed between them. plastic mesh. Aerated concrete walls are smooth, there is no need to prepare them, just remove dust. Finish - decorative plaster or lungs facing tiles from porous ceramics or concrete.
One of the options for the “wet” system. You cannot skimp on dowels, corners and mesh.
- "Wet" system is heavy
If you really want to clad the façade with stone or heavy ceramic slabs, you will have to use “heavy” technology. In this case, the insulation is not glued, but attached to the wall with powerful hooks, and a durable material is placed on top. metal mesh and fix the structure with metal plates. A thick (20-40 mm) layer is made over the mesh cement-sand plaster. Now you can place the stone. Such a system is significantly more expensive than a “light” one.
- "Dry" system
It is also called a ventilated or curtained façade. It involves constructing a frame outside the facade, metal or wood. Insulation is placed between its elements - inexpensive soft mineral wool or even cheaper glass wool, polystyrene foam. Sheathing the frame various materials: more often it is plastic or metal siding, wooden cladding board. Curtain facades from porcelain stoneware or stone slabs, colored glass for roads and residential buildings are rarely used. A “dry” facade, if you do not use expensive types of cladding, is cheaper, but less attractive from an aesthetic point of view.
Don't forget to leave air gap at least 2 cm between the insulation and the siding so that the walls have the opportunity to “breathe”
- Brick cladding
The last option is to cover the facade with brick. In this case, a frame is not needed; the insulation can be attached directly to the wall. An air gap should be left for ventilation of the insulation. Brick and the inevitable thickening of the foundation will cost a pretty penny.
To prevent the brick cladding from collapsing, it is secured to the main wall with anchors
To summarize, we get the following: the optimal solution in terms of price/efficiency/aesthetics ratio for temperate climatic zones of Russia is external insulation of aerated concrete walls mineral wool slabs 10 cm thick using “wet” technology. Acceptable budget options- “wet” foam facade or expanded polystyrene + plastic siding. Properly executed insulation of external walls will reduce heating costs by approximately half.
Aerated concrete blocks - due to their porous structure, have very high characteristics, such as thermal insulation material, but despite this, when building from cellular concrete and aerated concrete walls, it is still advisable to insulate them. Even if you have to spend money on additional thermal insulation, it will pay off for you, thanks to reduced energy consumption in the future, to maintain constant temperature in the house. Using aerated concrete adhesive is also very effective solution. But additional insulation houses made of aerated concrete, it will also not be amiss.
Choosing material for home insulation
For a house built from aerated concrete blocks, you need to select the right material for insulation. As when choosing any building materials for your home, you need to choose only high-quality ones from reliable and reputable manufacturers. For a house made of aerated concrete, there is a wide range heat-insulating materials. At first glance, it may seem that figuring out and choosing the right insulation for your home is quite difficult.
We recommend consulting with consultants working in this area; the thing is that the choice largely depends on the area in which you live, what the average annual temperature and humidity are. Depending on this, the appropriate insulation for the house and its thickness are selected.
House insulation work
Before you start insulating the house from the outside, you need to carefully check the quality of all the seams between the blocks and on the walls of the house. Also check out the finishing of aerated concrete walls.
Insulation of a house made of aerated concrete
Adviсe:
- Usage masonry adhesive for aerated concrete blocks, allows significantly reduce seams between blocks, and this in turn will lead to a reduction in heat loss.
- If any problems with seams, voids or anything else are found, we recommend using construction foam to eliminate them. After that, carefully putty and start insulating.
- Insulation of the house from the outside can be combined with insulation of the house from the inside, in order to be confident in the quality of the thermal insulation of your house.
Dew point in the wall
When is it produced? insulation of aerated concrete house, it is important to remember such a concept as Dew point in the wall. If there is no insulation, then this point is located in the thickness of the material; when the walls are thermally insulated, the point moves towards the heat insulator.
Due to this, very important use all finishing and heat-insulating building materials with high coefficient vapor permeability.
This allows moisture to escape without causing it to remain trapped inside. If any difficulties arise, you need to use ventilated facades. They effectively help cope with excess moisture and get rid of it.
Currently, there is great amount types of ventilated facades for houses made of aerated concrete blocks, for every taste and color, wood, brick and artificial stone.
Dew point in the wall - the temperature zone in which water vapor condenses and turns into water.
The dew point is highly dependent on air humidity, and the higher the humidity, the higher the likelihood of condensation.
The dew point is also affected by the temperature difference between inside and outside the room.
In this review, we are testing to find the dew point in a wall made of D500 aerated concrete. Will be considered different variants walls made of aerated concrete, for example, 200mm and 400mm thick, as well as using insulation.
What is the dew point in a wall
Calculations were carried out in the program teploraschet.rf
Density of aerated concrete 500 kg/m³ (D500).
Black line on the graph shows the temperatures inside the aerated concrete wall. Starting from 20 degrees Celsius and ending with -20 degrees.
Blue line shows the dew point temperature. If the temperature line touches the dew point line, a condensation zone is formed.
In other words, if the dew point temperature is always lower than the temperature in the aerated concrete, then condensation will not form.
As can be seen in the graph, the dew point in both cases is inside the aerated concrete, closer to the outside, and the amount of condensate is almost equal.
Aerated concrete and mineral wool (outside)
Now let’s look at what happens in aerated concrete if it is insulated with mineral wool from the outside.
| Aerated concrete D500 200mm + 50mm mineral wool | Aerated concrete D500 200mm + 100mm mineral wool |
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Option for insulating aerated concrete mineral wool(100mm) eliminates condensation. Moreover, there will be no condensation even if the temperature in the house is +25 and -40 outside. Moreover, 100mm mineral wool provides very good thermal insulation.
Aerated concrete and mineral wool (inside)
| 50mm mineral wool + aerated concrete D500 200mm | 100mm mineral wool + aerated concrete D500 200mm |
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As can be seen in the graph, internal insulation with mineral wool leads to significant condensation formation throughout the entire thickness of the aerated concrete wall.
Note interesting feature- the thicker the inner layer of mineral wool, the more condensation forms in the aerated concrete wall, which is extremely undesirable.
Important! Wet aerated concrete retains heat less well and breaks down faster.
Conclusion
It is better to keep the dew point in an aerated concrete wall closer to the outside. And it’s even better if the dew point is in the insulation, be it mineral wool or polystyrene foam. Note that polystyrene foam is not afraid of getting wet, and does not lose its thermal insulation properties, and mineral wool, when wet, greatly loses its properties as insulation.
Now very often the facade is insulated with mineral wool and covered with it facing bricks, leaving a ventilation gap that dries the mineral wool. Another popular method is plastered foam, which is much cheaper.
In order to understand what consequences the lack of a ventilated gap in walls made of two or more layers will lead to different materials, and whether gaps in walls are always needed, it is necessary to recall the physical processes occurring in the outer wall in the event of a temperature difference on its inner and outer surfaces.
As you know, the air always contains water vapor. The partial pressure of vapor depends on the air temperature. As temperature increases, the partial pressure of water vapor increases.
During the cold season, the partial vapor pressure indoors is significantly higher than outside. Under the influence of pressure differences, water vapor tends to enter an area of lower pressure from inside the house, i.e. on the side of the material layer with a lower temperature - on the outer surface of the wall.
It is also known that when air is cooled, the water vapor contained in it reaches extreme saturation, after which it condenses into dew.
Dew point- this is the temperature to which the air must cool so that the vapor it contains reaches a state of saturation and begins to condense into dew.
The diagram below, Fig. 1, shows the maximum possible content of water vapor in the air depending on temperature.
The ratio of the mass fraction of water vapor in the air to the maximum possible fraction at a given temperature is called relative humidity, measured as a percentage.
For example, if the air temperature is 20 °C, and humidity is 50%, this means that the air contains 50% of that maximum quantity water that may be there.
As is known, building materials have different abilities to transmit water vapor contained in the air, under the influence of the difference in their partial pressures. This property of materials is called vapor permeation resistance, measured in m2*hour*Pa/mg.
To briefly summarize the above, in winter period air masses, which include water vapor, will pass through the vapor-permeable structure external wall from inside to outside.
The temperature of the air mass will decrease as it approaches the outer surface of the wall.
In a dry wall there is a vapor barrier and a ventilated gap
The dew point in a properly designed wall without insulation will be in the thickness of the wall, closer to the outer surface, where steam will condense and moisten the wall.
In winter, as a result of the transformation of steam into water at the condensation boundary, the outer surface of the wall will accumulate moisture.
In the warm season this accumulated moisture must be able to evaporate.
It is necessary to ensure a shift in the balance between the amount of vapor entering the wall from inside the room and the evaporation of accumulated moisture from the wall towards evaporation.
The balance of moisture accumulation in the wall can be shifted towards moisture removal in two ways:
- Reduce vapor permeability inner layers walls, thereby reducing the amount of steam in the wall.
- And (or) increase the evaporation capacity of the outer surface at the condensation boundary.
They have the same resistance to vapor permeation throughout the entire thickness, as well as a uniform temperature change across the thickness of the wall. The boundary of water vapor condensation in a properly designed wall without insulation is located in the thickness of the wall, closer to the outer surface. This provides such walls with a positive balance of moisture removal from the wall thickness in all cases, except for rooms with high humidity.
In multi-layer walls materials with different vapor permeability resistance are used with insulation. In addition, the temperature distribution throughout the multilayer wall is not uniform. At the boundary of layers in the thickness of the wall we have sharp temperature changes.
To ensure the required balance of moisture movement in multilayer wall it is necessary that the resistance to vapor permeation of the material in the wall decreases in the direction from the inner surface to the outer.
Otherwise, if the outer layer has greater resistance to vapor permeation, the balance of moisture movement will shift towards the accumulation of moisture in the wall.
For example.
The resistance to vapor permeation of aerated concrete is significantly less than that of ceramics. At facade finishing For houses made of aerated concrete and ceramic bricks, a ventilated gap between the layers is required. If there is no gap the blocks will accumulate moisture.
Ventilated gap between facing masonry ceramic bricks And load-bearing wall made of expanded clay concrete blocks is not needed, because The vapor permeability resistance of brick cladding is less than that of a wall made of expanded clay concrete blocks.
If the wall is constructed incorrectly, moisture will gradually accumulate in the insulation.
Already in the second, or maximum third-fifth heating period, it will be possible to feel a significant increase in heating costs. This is naturally due to the fact that the humidity of the thermal insulation layer and the entire structure as a whole has increased, and accordingly the thermal resistance of the wall has significantly decreased.
Moisture from the insulation will be transferred to adjacent layers of the wall. Fungus and mold can form on the inner surface of external walls.
In addition to moisture accumulation, Another process occurs in the wall insulation - freezing of condensed moisture. It is known that periodic freezing and thawing of a large amount of water in the thickness of the material destroys it.
Wall materials vary in their ability to resist condensation freezing. Therefore, depending on the vapor permeability and frost resistance of the insulation, must be limited total condensate accumulating in the insulation during the winter period.
For example, mineral wool insulation has high vapor permeability and very low frost resistance. In structures with mineral wool insulation (walls, attic and basement floors, mansard roofs) To reduce the entry of steam into the structure, a vapor-proof film is always laid from the room side.
Without the film, the wall would have too little resistance to vapor permeation and, as a result, a large amount of water would be released and frozen in the thickness of the insulation. The insulation in such a wall would turn into dust and crumble after 5-7 years of operation of the building.
The thickness of the thermal insulation must be sufficient to maintain the dew point in the thickness of the insulation, Fig. 2a.
If the insulation thickness is small, the dew point temperature will be on the inner surface of the wall and vapors will condense on the inner surface outer wall, Fig. 2b.
It is clear that the amount of moisture condensed in the insulation will increase with increasing air humidity in the room and with increasing severity of the winter climate at the construction site.
The amount of moisture evaporated from the wall in the summer also depends on climatic factors - temperature and humidity in the construction area.
As you can see, the process of moisture movement in the thickness of the wall depends on many factors. The humidity regime of walls and other fences of the house can be calculated, Fig. 3.
Based on the calculation results, the need to reduce the vapor permeability of the inner layers of the wall or the need for a ventilated gap at the condensation boundary is determined.
Results of calculations of humidity conditions various options insulated walls (brick, cellular concrete, expanded clay concrete, wood) show that in structures with a ventilated gap at the condensation boundary, moisture accumulation in the fences of residential buildings does not occur in all climatic zones Russia.
Multilayer walls without ventilated gap must be applied based on the calculation of moisture accumulation. To make a decision, you should seek advice from local specialists professionally involved in the design and construction of residential buildings. Results of calculation of moisture accumulation standard designs walls at the construction site have long been known to local builders.
— this is an article about the features of moisture accumulation and insulation of walls made of brick or stone blocks.
Features of moisture accumulation in walls with facade insulation with foam plastic, expanded polystyrene
Insulation materials made from foamed polymers - polystyrene foam, polystyrene foam, polyurethane foam - have very low vapor permeability. A layer of insulation boards made of these materials on the facade serves as a barrier to steam. Steam condensation can only occur at the boundary of the insulation and the wall. A layer of insulation prevents condensation from drying out in the wall.
To prevent moisture accumulation in a wall with polymer insulation it is necessary to exclude steam condensation at the boundary of the wall and insulation. How to do it? To do this, it is necessary to ensure that the temperature at the boundary of the wall and the insulation is always, in any frost, above the dew point temperature.
The above condition for temperature distribution in a wall is usually easily met if the heat transfer resistance of the insulation layer is noticeably greater than that of the insulated wall. For example, insulating a “cold” brick wall of a house with polystyrene foam 100 mm. in the climatic conditions of central Russia it usually does not lead to the accumulation of moisture in the wall.
It’s a completely different matter if a wall made of “warm” timber, logs, aerated concrete or porous ceramics is insulated with polystyrene foam. And also, if you choose a very thin polymer insulation for a brick wall. In these cases, the temperature at the boundary of the layers can easily be below the dew point and, to ensure that there is no moisture accumulation, it is better to perform the appropriate calculation.
The figure above shows a graph of temperature distribution in an insulated wall for the case when the heat transfer resistance of the wall is greater than that of the insulation layer. For example, if a wall is made of aerated concrete with a masonry thickness of 400 mm. insulate with foam plastic 50 thick mm., then the temperature at the border with the insulation in winter will be negative. As a result, steam condensation will occur and moisture will accumulate in the wall.
The thickness of the polymer insulation is selected in two stages:
- They are chosen based on the need to provide the required resistance to heat transfer of the outer wall.
- Then they check for the absence of steam condensation in the thickness of the wall.
If the check according to clause 2. shows the opposite, then it is necessary to increase the thickness of the insulation. The thicker the polymer insulation, the lower the risk of steam condensation and moisture accumulation in the wall material. But this leads to increased construction costs.
A particularly large difference in the thickness of the insulation, selected according to the two above conditions, occurs when insulating walls with high vapor permeability and low thermal conductivity. The thickness of the insulation to ensure energy saving is relatively small for such walls, and To avoid condensation, the thickness of the slabs must be unreasonably large.
Therefore, for insulating walls made of materials with high vapor permeability and low thermal conductivity It is more profitable to use mineral wool insulation. This applies primarily to walls made of wood, aerated concrete, gas silicate, and large-porous expanded clay concrete.
The installation of a vapor barrier from the inside is mandatory for walls made of materials with high vapor permeability for any type of insulation and facade cladding.
To install a vapor barrier, it is made from materials with high resistance to vapor permeation - a primer is applied to the wall deep penetration in several layers, cement plaster, vinyl wallpapers or use a vapor-proof film. Published