Table of contents
- Why value is so important
- Dew point calculation - basics
- Determine the value using tables
- Calculate the value online
- Let a professional calculate the value
Above a certain temperature, water vapor turns back into water. This applies to the weather as well as to buildings. This is particularly important in masonry. It turns out that a wall is structurally so cold that water vapor gets inside falls, it is to be expected that the wall will become damp and, in the worst case, it will close mold growth occurs.
Why value is so important
Today's new buildings are always insulated to avoid high heat loss. However, this has the consequence that masonry no longer only consists of bricks and the overlying plaster. The wall structure is different, so depending on the type of construction, different insulation options are used, which have different thicknesses and are made of different materials. While in old houses the value was always outside the masonry, today it can be inside the wall due to the insulation. However, as soon as water vapor condenses in a wall, it becomes damp. Mold growth and structural damage can be the result. The insulation must be constructed using the dew point calculation in such a way that the value is outside the wall.
Dew point calculation - basics
There is no exact formula for calculating the point at which condensation occurs. In the construction industry in particular, many variables, some of which are variable, must also be taken into account. The three factors humidity, air pressure and temperature are sufficient to eliminate mold or to calculate the risk of mold growth. When planning the wall construction with different building materials, the properties of the respective building materials also come into play. In particular, the water vapor diffusion resistance, which determines how water vapor permeable the Material is the thermal resistance, which indicates how well the heat is conducted and the material thickness.
Determine the value using tables
As with the weather, air temperature and humidity can be used to create tables that show the temperature at which water vapor condenses. However, this is not an exact calculation. Depending on the table, the values are calculated using different air pressures. In order to use the correct table, it can make sense to read the air pressure on a manometer and look for a corresponding table. Then the room temperature and humidity are measured in the middle of the room. Both values can be determined with a thermometer and hygrometer. The dew points can be read at the points where the values in the table cross. To avoid moisture, the wall temperature should be above this point. The wall temperature is measured with an infrared thermometer.
A rule of thumb:
At a room temperature of 20 degrees and a humidity of 50%, the wall temperature must not drop below 10 degrees, otherwise mold can form due to moisture.
The higher the humidity and temperature, the higher the value at which water vapor condenses. This is why mold rarely forms in well-heated rooms without insulation, except in cold places, such as windows, because the water vapor condenses there.
It follows that when humidity is changed by ventilation or air temperature is changed by heating, the level at which water vapor condenses also changes.
Calculate the value online
You can have the value calculated online on various pages on the subject of insulation, building materials and dew point calculation. You also have to enter humidity and temperature for this, and sometimes also the air pressure. The programs then calculate the respective value and appropriate measures can be taken so that the wall temperature does not fall below this point.
Examples:
https://www.baumangel-schimmel.de/schimmelrechner
Some programs use the respective values of certain building and insulating materials, so that the calculation is even more precise, provided that it is known which building materials were used in the wall. These programs are also suitable for planning new insulation.
Example:
https://www.styrostone.de/u-wert.html
The wall structure consists of up to 5 building materials. The values for water vapor permeability and thermal resistance are necessary for an exact calculation.
Let a professional calculate the value
If you want to be on the safe side or plan a complete insulation from scratch, you can have the right value calculated by a professional. This ensures that no moisture collects in the living areas and the risk of mold is averted. Adequate ventilation and heating is still necessary. Especially with multi-layer insulation systems, it is important to determine the value at which moisture forms as precisely as possible so that it is outside the masonry and the insulation. Professionals calculate this point using software simulations that use different formulas and variables. The costs for a professional invoice depend on the scope and effort, it is best to have an individual offer made.
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