Independent insulation of a house made of aerated concrete is simple and inexpensive. Dew point in a wall - what is it in practice Dew point of aerated concrete how to calculate

Determining the dew point in a wall is very simple. Below is an example of how to make the calculation. This can be done by anyone who is interested in the issue of proper insulation.

The dew point is the temperature at which water vapor begins to condense.

What is dew point

The dew point in a wall can move across its thickness as indoor and outdoor temperatures change. For example, if the temperature inside the room is stable, but it gets cold outside, then the dew point will move along the thickness of the wall closer to the room.

The temperature of the object on which steam will begin to condense, i.e. dew point depends mainly on two parameters:

• air temperature;
• air humidity.

For example, if the indoor temperature is +20 degrees and the humidity is 50%, the dew point temperature will be (approximately) +12.9 degrees. If an object with this temperature or lower appears in the room, condensation will form on it.

For example, when a refrigerator is opened, dew falls inside it from the incoming warm air. It looks like "fog coming from the refrigerator."

If it is cold outside, then somewhere in the wall there will be a temperature at which steam condensation will begin, and at this point there will be humidification. If the wall is thin, “cold”, and its inner surface cools to 12.9 degrees or less (at the specified temperature and air humidity), then dew will fall on it, it will become wet, and will very quickly acquire mold.

When insulating walls and house structures, it is useful to calculate the dew point for the largest and lowest values humidity and temperature, in order to know within which boundaries of space the dew point will move when these parameters change.

How the calculation is performed

When calculating the dew point and insulation thickness, some parameters are not taken into account - pressure, air speed, material density... Therefore, we can only talk about approximate values. But this is not critical when we're talking about on determining the thickness of the insulation.

To determine the dew point in a wall, the easiest way is to use tables of ready-made approximate values, and not try to do the calculations yourself. Moreover, you should not trust homemade programs from the Internet; they often do not take into account parameters and produce false values, and sometimes based on the principle of random numbers.

Below is a table of calculated dew point values ​​depending on air temperature and humidity. These are approximate values, as the influence of other factors is not taken into account.

For example, you can determine that for a room with an internal temperature of +22 degrees and a humidity of 60%, the temperature at which water vapor will condense (dew point) will be 13.9 degrees.

A wall with insulation - how to determine the location of condensation

Solving the problem of finding the dew point in a wall is very simple.
Need to know:

• wall thermal resistance coefficient, ?1, W/(m K);
• coefficient of thermal resistance of insulation, ?2, W/(m K);
• wall thickness, h1, m;
• insulation thickness, h2, m;
• indoor temperature, t1, deg. WITH;
• air humidity that will reach the dew point,%;
• dew point for temperature and humidity data, deg. WITH;
• outside temperature, t2, deg. WITH.

As a rough approximation, it is assumed that the temperature throughout the thickness of each layer will change linearly.

The desired value is the temperature at the boundary of the layers of the wall and insulation. When it is found, you can build a graph of temperature changes in the “wall-insulation” layer and use it to find the position of the dew point.

To do this, the ratio of the thermal resistance of the wall to the thermal resistance of the insulation is found, based on which the change in temperature in one of the layers is determined, which will make it possible to find out the temperature at the boundary.

Let's look at an example.

Calculation example

An example of conditions is as follows.
Reinforced concrete wall h1=36 cm, insulated with polystyrene foam h2=10 cm. Thermal resistance coefficient of reinforced concrete?1=1.7 W/cmK, foam plastic -?2=0.04 W/cmK. Temperature inside t1=+20 degrees, outside t2=-10 degrees. Humidity indoors and outdoors is assumed to be the same - 50%. According to the table, the dew point will be 9.3 degrees.

Thermal resistance of the wall and insulation is defined as h/?, W/m2K.
In this example, the thermal resistance of the wall will be 0.36/1.7=0.21 W/m2K, insulation 0.1/0.04=2.5 W/m2K.

The ratio of thermal resistances of the first layer to the second (walls to foam plastic) will be: n=0.21/2.5=0.084.
Then the temperature difference in the first layer (wall) will be T = t1- t2xn = 20-(-10)x0.084 = 2.52 degrees.

Accordingly, the temperature at the layer boundary will be equal to t1-T=20-2.52=17.48 degrees.

Now we can build an approximate graph of temperature differences in the wall-insulation layer on a scale and mark the dew point on it.

From approximate calculations and an approximate graph, you can find out the main thing - the dew point is in the insulation, far from the wall, i.e. even worsening conditions, taking into account the calculation errors, will not lead to harmful moisture in the wall.

An example of determining the location of the condensation temperature inside a wall

The temperature inside is +22 degrees, outside - 15 degrees (region to the north), humidity - 50%, dew point - 11.1 degrees. A wall 38 cm thick is made of brick (1.5 bricks + joint + plaster is taken as “brickwork”).

Thermal resistance coefficient for brickwork- 0.7 W/cmK, for mineral wool - 0.05 W/cmK (taking into account its moistening in real conditions operation).

Thermal resistance of the wall: 0.38/0.7=0.54 W/m2K, insulation 0.1/0.05=2.0 W/m2K.
The ratio of the thermal resistances of the first layer to the second will be: n=0.54/2.0=0.27, and the temperature difference within the first layer will be T=22 - (-15)x0.27=9.99 degrees. Temperature at the boundary of layers: 22 - 9.99 = 12 degrees.

As we see, the situation is “butt-to-end”. With increasing humidity, that common occurrence, with a drop in indoor temperature, or in cold winter, the dew point will “walk” inside the wall.

Such insulation for a relatively “warm” brick wall, will already be considered insufficient, both according to the position of the dew point and according to the standard values ​​of heat loss through the enclosing structures.

The dew point can be moved by heating the room using internal heating and dehumidifying it. Naturally, this is an extreme measure, which is used only when it’s time to “dry the walls.”
Dew point in the wall - calculation and determination

What values ​​should be taken for calculation

Typically, the indoor temperature is 22 degrees, more often it is lower near the floor, and reaches 27 degrees near the ceiling. For central regions, the minimum outdoor temperature is considered to be -15 degrees (short-term temperature drops to -20 - -25 degrees are allowed).

For southern regions- -7 degrees, with a short-term drop of -15 - -20 degrees.
(You can choose the minimum temperature yourself - what temperature is constantly maintained in winter? To what values ​​does it drop for a short time?)

The air humidity in the room is usually assumed to be medium (but not low) - 50%. There is usually some reserve here, since often in winter the indoor air is drier due to actively working heating - 30 - 40%. But many homes combat dry air by installing humidifiers and growing plants. The optimal humidity is 50%, which is also the calculated one.

In autumn and spring, steam will flow through the insulation in the opposite direction - from the street. To calculate the “demi-season” according to vapor-permeable insulation, humidity should be about 90%.

Where should the dew point be?

The insulation of a fence is considered “normal” only when the dew point in cold weather is mainly (!) located in the insulation and does not move into the wall.

What does "mostly" mean?
At maximum negative temperatures, which usually last several days, a week, and occur periodically, the dew point can shift into the wall.

For a dense wall heavy materials, there is nothing dangerous about it. But for walls made of porous materials, which, as usual, transmit steam very well and absorb moisture, the appearance of the dew point should be short, especially when they are combined with vapor barrier insulation.

Such walls require the most insulation, especially considering that they themselves are warm. To shift the dew point you will need 2 times more insulation. They combine much better with vapor-transparent insulation, since moisture can be removed here, but only if the insulation has excellent ventilation.

Visual temperature graphs for various schemes insulation. The dew point is approximately indicated as 16 degrees, achieved when the inside of the house is especially comfortable at +25 degrees, 55 - 60% humidity.

• 1 - wall without insulation;
• 2 - insufficient insulation layer - the dew point is inside the wall. Its constant presence will cause a leaky wall to become wet, an unhealthy atmosphere, and the danger of destruction of the material if the wall insulation layer has greater resistance to the movement of steam than the wall itself (improper insulation);
• 3 - sufficient insulation, dew point in the insulation (most of the time), normal preservation of wall materials and heat in the house, if the thermal resistance of the structure is not less than the standard one, because for very cold walls it is possible to shift the dew point from them with a small layer of insulation;
• 4 — internal insulation – worst solution. The dew point on the surface of the wall or close to it leads to the wall getting wet, and damage to the health of residents, wet freezing and destruction of structures. Applicable in hopeless situations provided that the wall is completely covered with a vapor barrier insulation, which prevents the penetration of steam to the dew point. Those. condensation is impossible due to humidity close to 0.

The standards indicate the thermal resistance of enclosing surfaces for specific climatic zones. The state forbids us to reduce this value.

More often, the standard requires a thinner insulation thickness than what is needed to shift the dew point into the insulation. Therefore, it is, in principle, desirable to select insulation for all surfaces and according to the condition of shifting the dew point into the insulation.

These values ​​are compared with regulatory requirement, but is usually accepted higher value, a multiple of the thickness of the insulation that is on sale.

Aerated concrete blocks are very popular for construction residential buildings, dachas and households. buildings During construction, there is a clear saving on the price of the wall itself, on insulation and finishing, and perhaps even on the foundation... Many consider porous concrete the most suitable materials for a home. But not everything is so simple and unambiguous. Let’s consider what negatives users found in aerated concrete based on operating experience, and what experts point out.

Aerated concrete is universal and inexpensive

Factory aerated concrete produced in an autoclave has a very exact dimensions, well-known characteristics, is also environmentally friendly - it does not highlight anything. For the construction of walls of residential buildings, grades D400 (400 kg/m3) and D500 are usually used.

Precision manufacturing allows you to apply a thin layer of glue when laying and make the wall surface almost flat. It is enough to apply fairly thin and cheap layers of plaster on the wall. But if the vertical joints in the masonry were not filled (usually), then to prevent increased air permeability, it is necessary to have plaster on both sides, usually 10 mm thick.

Aerated concrete is very light. Therefore, a foundation can be designed with less bearing capacity, which should also be cheaper, it seems...

The walls may not be insulated

D400 is less durable, but more heat-saving. So, for the climate of the Moscow region, if the humidity of the block is not increased, and the masonry is made at thin layer glue or on a heat-saving solution, then the thickness of the wall made of it, which meets the heat-saving requirements, will be only 46 cm. That is. actually the length of one block.
For the D500, this value is actually already about 63 cm.

But, as you know, heat loss at home should not generally exceed certain standard values. Even standards allow increased heat leakage through some structures, provided that they are compensated by increased thermal insulation in other places.

Therefore, if everything is in order with the thermal insulation measures on windows and doors, floors, foundations and roofs, and the ventilation of the building is according to the standards, then insulating aerated concrete walls of large thickness is not an economically profitable measure.

The absence of an insulating layer is very significant savings compared to cold materials for wall construction.

In addition, a single-layer wall is simpler and cheaper, more trouble-free not only in construction, but also in maintenance; during operation, you do not need to expect surprises from it, in the form of shedding or wetting of the insulation...

The foundation you need is not cheap

The foundation may have a lower load-bearing capacity, but is much more rigid than for brick. Does not allow bending. In fact, it is even more expensive than usual. Aerated concrete is very fragile, and a crack in the wall due to improper laying with the formation of local stress, especially when installing lintels and reinforced belts, is a common occurrence.

Moreover, movement of the foundation is unacceptable. Requires an expensive tape reinforced concrete foundation increased rigidity - only it can save the situation and prevent cracks from occurring. Its design and dimensions are specified in the project, but it is by no means cheap...

The need for proper masonry and use of armored belts

It has already been said that the creation of point stresses, for example, from a beam above a window, can lead to the destruction of a wall made of aerated concrete. It is necessary to involve only competent specialists for construction in order to avoid too costly mistakes.

Also, to avoid point loads, it is necessary to create reinforced belts, for example, create concrete belt under the beams attic floor. And also competent thermal insulation of this concrete. All this is quite complicated and not cheap.

In addition, the strength of aerated concrete, as a rule, even with an armored belt, is not enough to support heavy rigid concrete floors. Only wooden beams are possible.

Difficult to use

Question of external plaster or additional insulation not so simple. If the plaster crumbles or cracks, then blow-out may occur in masonry with empty vertical joints. Residents will not understand why it is cold.

The second question is not correct selection by vapor permeability. Aerated concrete itself is very vapor transparent, so outer layer on such a wall it must have less vapor permeability than the masonry itself, otherwise the blocks will get wet.

If external plaster(insulation) and paint, for some reason, or due to your own Low quality find themselves with great resistance to the movement of steam, then a very serious problem will arise. And the residents again won’t know about it. So there's a risk artificial creation There is moisture accumulation in the material...

Risk of destruction by water

The material is quickly destroyed by water. A wet wall made of aerated concrete cannot exist for long. This is aggravated by freezing. Violation horizontal waterproofing on the foundation (basement), capillary suction of water into the masonry from the ground - and how to save the house is not yet known...

• If the roof is damaged, there may be a water leak and a wet wall not noticed in time...
• Violation of vapor exchange, due to an incorrect outer layer, as indicated, can lead to detrimental consequences...
• Humidification by precipitation in the appropriate seasons, with unreliable façade finishing...

In general, the thoroughness of waterproofing measures during construction and during operation should be the highest. You need to monitor the condition of the walls... Will it be possible to keep all the walls dry?

Difficulty hanging anything

Everyone is accustomed to the fact that the heating boiler is “hanging”, half kitchen set- hung on the wall, boiler - “well, it’s not worth it.” But how to do this when the walls and partitions are made of porous lightweight material, like pumice?

There are special dowels for fixing to aerated concrete. But they are more expensive. And the fastening cannot be called reliable.

As a result, under heavy objects, either they put a metal frame on the wall and hang everything on it, or they glue a couple more sheets of cement particle board onto this wall...

A nail that doesn't stay in the wall is a problem and not a convenience.

Something needs to create heat capacity

Aerated concrete is too light and practically does not accumulate heat. But the house must have temperature stability. It's extremely uncomfortable without her. In a brick house, comfort is achieved by using a large array of heavy materials. And no matter how the temperature outside changes overnight, no matter how much the door is opened, everything in the house is stable.

In houses made of SIP panels, this function is performed by heated ventilation.

But what to do in aerated concrete? Don't resort to expensive but untrustworthy fans made from frame houses. It remains to place tens of tons of concrete in a heated floor, for example, or in massive interior partitions. In general, there is one more “but” that needs to be solved...

What is the durability of aerated concrete?

WITH brick house everything is clear - he is, relatively speaking, “eternal.” And they don’t give any guarantee for aerated concrete... There are no known facts that the manufacturer guarantees anything and promises to fix it if problems arise.

There are already more and more reviews that aerated concrete is starting to crumble. The service life of a wall under load is a maximum of 40 years for high-quality factory-made aerated concrete in a frosty climate... There are many such reviews, and entire aerated concrete walls older than 50 years are found only where the temperature does not pass through 0. Probably various shortcomings mentioned above in combined, plus the state of stress under load with changes in humidity and freezing, leads to the fact that the blocks are covered with a web of cracks. Which only diverge over time.

However, this material is still considered new, and extensive experience of its long-term operation has not been accumulated with clear conclusions. But there is no refutation of the above data yet...

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. He's the same 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 an analogue of cellular concrete with a thickness of 300 mm. 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 best option insulation: “thermal fur coat” using hard mineral wool slabs 100 mm thick

There is another 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 a building so that it can be passed on intact to great-grandchildren.

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 condenses maximum amount moisture 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 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 interior decoration. 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 there is no finishing anywhere on the surface of the polystyrene foam boards, the Mickey Mouse family will immediately make a cozy hole there and settle in. 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 are easy to eliminate 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 topics, which 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 most human-friendly 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 insulating 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 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 save 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 are developing integrated technologies and to help performers they create clear, very detailed and well-illustrated manuals. 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 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 made of porcelain stoneware or stone slabs, colored glass, 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 brick cladding has not collapsed, it is attached 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 with 10 cm thick mineral wool slabs 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.

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

The option of insulating aerated concrete with 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

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 inner layer mineral wool, the more condensate forms in 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 ventilation gap, which dries mineral wool. Another popular method is plastered foam, which is much cheaper.

The question of the need to insulate walls made of aerated concrete arises due to the fact that in most regions, due to low winter temperatures The thermal resistance of this material is not sufficient for standard values.

In addition, as a result of the phenomenon of moisture condensation in the thickness of aerated concrete, its thermal resistance is further reduced and its service life is reduced.

To understand the condensation of water in a wall, let’s remember what’s actually happening in it. Water in nature can have three states. This liquid state- rivers, seas and oceans, water in the water supply, - solid - snow and glaciers - and also gaseous - these are moisture vapors in the air. Water vapor is not clouds or fog, it is water molecules contained along with other gas molecules in the air. And clouds and fog are moisture that has already condensed from the air.

Almost any wall of a residential building has a certain breathability, which indicates that there is air in its thickness. And since air is present, water vapor is also present with it. And these vapors, these water molecules tend to move to where it is freer, where the air humidity is lower.

Thus, there is a constant movement of these moisture vapors through the walls. In winter, when the humidity of the outside air is low, water vapor moves in the air of the wall from the inside to the outside. And in the summer, if the humidity of the outside air rises so much that it becomes higher than the humidity inside the house - on the contrary, from the outer surface of the wall inward.

This is the process called wall breathing. This should not be confused with air movement through walls. The air in the wall is practically motionless, since Atmosphere pressure the same both in the house and outside.

Let us now remember what the dew point is, that is, the temperature at which water vapor in a saturated state begins to precipitate in the form of condensate and turns from a gaseous state to a liquid one. This dew point depends primarily on the saturation of the air with water vapor, which can be seen in this video.

Examples of wall insulation with calculation graphs are shown in the attached video. It is clear that these calculations did not take into account other structural elements, plasters, membranes and cladding, it was only important to compare various insulation materials in their use with aerated concrete.

But it was especially important to understand how the vapor permeability coefficient of the insulation affects its performance. And all these examples fully confirm the construction rule multilayer wall: the vapor permeability coefficient of each layer should increase in the direction from inner surface structures to the outside.

And one more thing about hydration. We just saw that it is impossible to completely avoid wetting the wall, as such. Various insulation materials behave differently, but each has the outside air temperature at which condensation inevitably begins to form in the wall.

And you need to choose a design in which this humidification would be the least at minimum temperatures in the region. The less moisture accumulation in the wall over time winter period, the easier and faster the wall will dry with the onset of summer season. And of course, do not forget about the standard thermal resistance in the region of development.