I built the walls, put the house under the roof and put the windows - the box is ready. It is at this stage that the “constructive” period of construction ends and the installation of equipment begins, the insulation of the walls of the house and its further preparation for fine finishing.
And it is at this stage that it is important to properly mount the insulation, and indeed the whole insulation pie on the walls of the house, so as not to get yourself such headache, like the dew point in the wall from the side of the dwelling.
What kind of beast is the dew point and why is the dew point in the wall bad, how does it look in practice?
First, a little theory, and then practical examples from own experience, which I received by purchasing a box at home with a layer of insulation already installed.
Dew point temperature
The dew point tends to move. This moment depends on two indicators - temperature and humidity.
Each of them is also divided in half - into the temperature in the room and on the street, on the humidity in the room and on the street.
All calculations and formulas that are used to calculate the dew point assume that moisture will condense from the vapor as it moves from the inside to the outside. This is exactly the situation that occurs in winter, when the temperature and humidity in the room are higher than the temperature and humidity outside. The dew point temperature will be calculated at the design values for outdoor and indoor conditions.
In summer, when the outdoor humidity and temperature are usually higher than the indoor humidity and temperature, the dew point does not matter as much. Why? Because the temperature difference is low and both temperature indicators, street and brownie, are in positive values.
And also because even if the dew point in the wall could form at positive values of both temperatures, this would not have a strong effect on the comfort of living in the house.
Another thing in winter. Moisture condensed from steam at low temperatures enters the insulation and the wall, and freezes there. For a heater, getting wet is fraught with either a complete loss thermal insulation properties(basalt wool), or destruction when water freezes (polystyrene). For the wall, everything is the same, especially for aerated concrete and gas silicate blocks.
I myself personally observed the sad picture of the destruction of the wall of a block house in the winter due to improperly made insulation. By spring, there were almost through holes in the gas silicate wall 400 millimeters thick.
How to calculate dew point
To calculate the dew point, a table of water vapor condensation values is used, depending on the humidity and temperature indicators. The value of the external and internal temperature and the value of the external and internal humidity are taken. It turns out the dew point temperature at which water will fall out of water vapor (dew formation).
What does this temperature give us? A lot of things. We are able to calculate where the steam will condense in the insulation pie, that is, where the dew point will be in the wall - in the insulation, in the load-bearing wall or on inner surface load-bearing wall - right in the room.
Naturally, the most correct option is the dew point in the heater. In this case, there will be no negative points for interior spaces. So that there are also no negative aspects for the insulation, it is worth choosing the right type of insulation for the walls at the planning stage.
A less acceptable option is the dew point in the wall of the house, which is the carrier. Here, the negative points for the interior will depend on the material of the wall. It turns out such a situation when the insulation is mounted incorrectly or the thickness of the insulation is incorrectly selected.
The most unacceptable option is the dew point inside the room, on the inner surface of the load-bearing wall. This usually happens when the house is not insulated at all or is insulated incorrectly - from the inside.
Dew point in the house - what to do?
So, the promised example from my own experience. I purchased a box brick house, which was insulated from the inside with foam. What the people who built this box were thinking about, one can only guess. Thanks to this insulation, a dew point was obtained in the house, on the inner surface bearing walls, between brick and insulation.
What was the dew point in the house, in what negative moments?
There were two. Firstly, the brick wall from the inside was always damp in small pluses and sub-zero temperatures. There was a musty smell in the rooms, when opened, there were large pockets of mold under all the foam plastic.
Secondly, in sub-zero temperatures it was impossible to heat this house normally, brickwork was excluded from the thermal circuit of the house, due to the fact that it was cut off from warm air rooms with foam.
What did I do to beat the dew point in my house?
Firstly, all the foam was dismantled from the inner surfaces of the load-bearing walls.
Secondly, the insulation was mounted outside and was plastered using the wet facade technique.
And thirdly, instead of the former internal insulation 50 millimeters, external insulation of 150 millimeters was installed.
At proper insulation- dew point outside, in the house - warm and dry.
What happened? It was warm, dry and comfortable.
FINAL NOTE. Do not create an air gap between bearing wall and room air. Walls are often sheathed from the inside of the GKL - it's cheaper and faster than plastering. However, micro drafts form in the air gap between the gypsum board and the brick, which prevent heat transfer and heating of the inside of the brickwork.
I am mine brick walls plastered from the inside with the most ordinary plaster mixture. From above, you can now paint or glue wallpaper. The thickness of the wallpaper is such that they, as a heat insulator, can be neglected.
Insulation of the house allows not only to live in comfort, but also to pay less for heating. The process of insulation begins with the choice of the method of thermal insulation and the selection of thermal insulation materials. At first glance, everything seems simple: add a layer of good thermal insulation material to the thickness of the wall and enjoy the warmth and comfort!
In reality, everything turns out to be much more complicated. There are a lot of videos on the Internet with stories about mold on the walls and the destruction of buildings, the cause of which was only improper insulation of the building, or rather, the position of the dew point inside the house or in the wall array, which led to the accumulation of moisture on the surface of the walls.
The correct determination of the dew point in the wall is the main condition for conducting high-quality, reliable and effective insulation Houses.
In physics, the dew point is the temperature at which the water vapor present in it, at constant pressure, changes from a gaseous state to a liquid state. In this case, condensation forms in the air, or, as is often said, dew falls.
The dew point is inextricably linked to the concentration of water vapor in the air: the higher it is, the higher the dew point temperature. A simple example, in a bathhouse, in a steam room, condensate forms even at a temperature close to 100 C. To form water droplets in a steam room, it is enough to come into contact with any surface, the heating of which is at least slightly below its temperature.
The concentration of water vapor in the air is called humidity. A hygrometer is used to measure humidity. In a residential area at an air temperature of 20-25 C, humidity of 40-60% is considered normal.
You can determine the dew point for a dwelling using heat engineering tables.
For an average residential area, its value is in the range from 6 to 12 C. This means that on any surface that has a temperature equal to the dew point temperature and below it (12 C and below), placed in a residential area, condensation is bound to form. It is this phenomenon that can be observed on the surface of bad windows in the cold season.
And what about the walls?
You ask, because their inner surface in a heated apartment or house is always warm and has an ambient temperature, and in places where radiators are installed, it exceeds it.
Indeed, condensation does not form on the inner surface of the walls ... until you decide to insulate them from the inside, using any heat-insulating material you like for this. It doesn't matter if you take a vapor-permeable insulation based on stone wool or give preference to non-polystyrene - the effect will be approximately the same. Over time, moisture forms on the inner surface of the walls under the insulation layer, the accumulation of which can lead to mold. This is due to the dew point on the inner surface of the walls.
Where is she, the dew point?
The temperature of the inner surface of the wall of the house is equal to the temperature of the room, and the temperature outer surface the walls of the house is equal to the temperature environment. In the cold season, there may be a temperature difference between inside and outside of 30 degrees or more.
Heat loss through the surface of the wall can be represented graphically by connecting the temperature mark inside and outside the house with a straight line. The temperature drop in the thickness of the wall is gradual and the more intense, the smaller the thickness of the wall or the higher the thermal conductivity of the materials from which it is made, but in any case, with a homogeneous composition of the wall (for example, only from brick), the dew point temperature (12 C and below) will be inside the wall.
It is here, inside the wall, that condensation occurs, which leads to freezing of the walls and their destruction during repeated cycles of freezing and thawing. For this reason, it is recommended to heat the house constantly, maintaining the temperature of the walls at the same level, trying to exclude periods of thawing of the building and new freezing.
It should be noted that no matter what material the house is built from, its walls are always vapor-permeable to one degree or another. There is always some moisture inside the wall.
If the walls are insulated from the inside
With the location of the heat-insulating material from the inner surface of the walls (Fig. 1), the main temperature drop will fall on the thickness of the heat-insulation. As a result, the temperature of its surface inside the house will be equal to the temperature of the room, and the temperature of the outer surface, depending on the thickness of the heat-insulating material and its quality, will be below the dew point temperature. At the same time, the temperature of the wall behind the thermal insulation layer will be even lower by 1-3 C, which will invariably lead to condensation.
It turns out that the water vapor in the house, trying to get out, passes through the heat-insulating material, cools down and condenses on the inner walls without getting into their thickness, even if construction material with good vapor permeability.
There can be only one conclusion: it is impossible to insulate the house from the inside!
How to bring the dew point outside?
When the thermal insulation material is located outside the walls, the ambient temperature will not be the wall, but the outer layer of thermal insulation. The temperature drop graph in this case will be more gentle, and the dew point temperature on it, depending on the temperature difference outside and inside the house, will be outside the wall in the thickness of the heat-insulating material or in the wall, but in close proximity to its outer surface.
It turns out that the thicker the thermal insulation layer, the more likely it is that the dew point is outside the wall, which means that the walls of the house that are well insulated from the outside will always be dry, which will increase the life of the building.
How to calculate dew point?
To calculate the dew point in the wall, the method for designing the thermal protection of buildings is used, which is detailed in the Code of Rules for the Design and Construction of SP 23-101-2004. An approximate primitive calculation is unlikely to help in this.
You can get reliable results using the services of the relevant online calculators which are easy to find on the internet.
What thermal insulation material to prefer
The concept of the dew point in the wall allows you to better understand and imagine the physical processes associated with the loss of heat through the plane of the wall and to choose the right heat-insulating material, while determining the methods of its installation.
As a rule, you have to choose between mineral wool and polystyrene foam.
Thermal insulation materials based on mineral wool differ in vapor permeability and when the dew point is found in their array, they do not interfere with the movement of steam and its release to the outside, into the atmosphere. Of course, we are talking about only part of the water vapor. The rest will turn into water and flow down the insulation layer. By the way, everything thermal insulation materials made of basalt and fiberglass are resistant to moisture, are not subject to mold and perfectly tolerate repeated cycles of thawing and freezing. So the position of the dew point in the thermal insulation layer will not harm it.
Expanded polystyrene is not vapor permeable. Therefore, moisture will accumulate on its inner surface. To remove it between the wall and the thermal insulation layer, you need to leave a groove, making guides in them. Only in this case can we talk about the safety of the walls and the high quality of their insulation.
