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Back to Knowledge Hub23.06.2026
The dew point is the temperature at which the moisture contained in the air can no longer be fully retained as water vapor. When the air cools to this point, excess moisture begins to condense and turns into liquid water.
The dew point is therefore a key parameter for assessing moisture risks in buildings. It does not describe the actual amount of moisture present but rather the critical condition at which condensation can form on building component surfaces.
Air can hold different amounts of moisture depending on its temperature. Warm air has a significantly higher capacity to retain water vapor than cold air.
If the air temperature decreases without moisture being removed, the relative humidity increases. Once a relative humidity of 100 percent is reached, the dew point has been reached.
The result: water vapor settles on colder surfaces as condensation.
An indoor air temperature of 22°C with a relative humidity of 60% corresponds to a dew point of approximately 14°C.
If there is a surface in the room with a temperature of 14°C or lower, condensation can form there. Typical areas include:
The higher the humidity in the room rises, the higher the dew point becomes. As a result, even less severely cooled surfaces can be enough for condensation to form.
The dew point plays an important role in the planning and operation of modern buildings.
Particularly in airtight buildings, moisture generated by occupants and daily activities can quickly accumulate in the indoor air. Typical sources of moisture include:
If this moisture is not removed sufficiently, relative humidity increases. This raises the dew point and increases the risk of condensation.
From a technical perspective, surface temperature alone is not the deciding factor. Equally important is controlling indoor air humidity through adequate air exchange.
Key takeaway: The higher the humidity, the higher the dew point—and the greater the risk of condensation on building component surfaces.
Condensation forms when humid air comes into contact with a surface whose temperature is below the dew point of the indoor air. At that moment, the air can no longer retain all of its water vapor. The excess moisture settles on the surface as water.
This process is easy to observe in everyday life: fogged windows, humid bathroom mirrors, or water droplets on cold pipes are visible forms of condensation.
The critical factor is not the room temperature but the temperature of the specific surface.
For example, if a room contains air at 21°C and 60% relative humidity, the dew point is approximately 13°C. If a window surface or thermal bridge cools to this temperature or below, condensation will form there.
Typical critical areas include:
The higher the humidity in the room, the less these surfaces need to cool for condensation to occur.
Modern building envelopes are significantly more airtight than older construction methods. While this reduces energy losses, it also means that more moisture remains inside the building if adequate air exchange does not take place.
Moisture is generated daily through normal building use:
Without sufficient air exchange, relative humidity continues to rise. This also increases the dew point and the risk of condensation.
Individual water droplets on a pane of glass are usually not a problem. Condensation becomes problematic when it occurs regularly or continuously.
This can lead to:
For this reason, condensation is often considered a warning sign of an imbalance between moisture input, temperature conditions, and air exchange.
Key takeaway: Condensation does not occur randomly. It is the direct result of a combination of high humidity, excessively low surface temperatures, and insufficient moisture removal.
Whether condensation forms depends primarily on three factors: humidity, air exchange, and surface temperature.
The higher the humidity, the higher the dew point. As a result, even moderately cooled surfaces can be enough for condensation to form.
High humidity therefore directly increases the risk of condensation.
Moisture is constantly introduced into the indoor air through occupants, cooking, showering, and cleaning activities. If this moisture is not removed, relative humidity continues to rise.
Insufficient air exchange promotes condensation because moisture remains inside the building.
Window connections, building corners, and other thermal bridges often have lower surface temperatures than the surrounding building components.
If these areas fall below the dew point of the indoor air, condensation forms.
Condensation usually occurs when several factors are present at the same time: high humidity, insufficient air exchange, and cold surfaces.
The more moisture accumulates in the building, the less a building component needs to cool for condensation to form.
Moisture is generated continuously in buildings. Without sufficient air exchange, relative humidity rises, which also increases the dew point. As a result, the risk of condensation increases.
Regular air exchange removes humid indoor air and replaces it with drier outside air. This reduces the moisture load and helps stabilize the indoor climate.
Window ventilation can effectively remove moisture but depends on user behavior. In practice, it is common that:
The result can be permanently elevated humidity levels within the building.
Continuously operating ventilation systems provide regular air exchange and help keep moisture levels under control over the long term.
As a result, they can:
Decentralized ventilation systems enable user-independent air exchange and can therefore make an important contribution to moisture protection. Ventilation systems with heat recovery (HRV) additionally combine controlled ventilation with energy-efficient operation.
Continuous air exchange reduces the moisture load within the building. This lowers the likelihood that building component surfaces will fall below the dew point and condensation will form.
| Room temperature | Relative humidity | Dew point | Condensation risk |
|---|---|---|---|
| 20°C | 40% | approx. 6°C | low |
| 20°C | 50% | approx. 9°C | low to moderate |
| 20°C | 60% | approx. 12°C | elevated |
| 20°C | 70% | approx. 14°C | high |
These values illustrate the relationship between humidity and the dew point: as humidity increases, so does the temperature at which condensation begins. As a result, even relatively warm surfaces can become a moisture-related problem.
The dew point is the temperature at which water vapor in the air turns into condensation. If a surface becomes colder than the dew point of the indoor air, moisture can settle on that surface.
Window surfaces are often among the coldest surfaces in a room. If their surface temperature falls below the dew point of the indoor air, condensation forms on the glass or frame.
Relative humidity directly affects the dew point. The higher the humidity, the higher the dew point and the greater the risk of condensation.
Three factors are essential:
This reduces the likelihood that surfaces will fall below the dew point.
Yes. Ventilation systems continuously remove humid indoor air and support consistent air exchange. This can reduce humidity and lower the risk of condensation. Decentralized ventilation systems with heat recovery (HRV) additionally combine this moisture protection with energy-efficient operation.
For more information on the dew point, the Ventomaxx blog offers additional articles that explore the relationship between humidity, condensation, and ventilation in greater depth. The article “High Humidity Despite Ventilation? Causes and Tips” explains why moisture can remain inside a building even with regular ventilation and the technical reasons behind it. The article “Humidity Sensor: Function, Benefits and Key Questions Explained Simply” provides practical insights into how humidity levels can be monitored and controlled in buildings. It explains how humidity sensors support demand-controlled ventilation and help reduce moisture accumulation, condensation risks and potential mould growth.
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With Ventomaxx, you gain access to comprehensive hybrid ventilation concepts that seamlessly combine passive and active systems from a single, trusted source. Our mission is to improve indoor air quality in the most efficient way.
We provide architects and technical planners tailored solutions to address every ventilation challenge with precision. Whether it is sound insulation,
energy efficiency, or optimising facade aesthetics, our expert technical teams are equipped to provide you with the ideal solutions.
With Ventomaxx, you gain access to comprehensive hybrid ventilation concepts that seamlessly combine passive and active systems from a single, trusted source. Our mission is to improve indoor air quality in the most efficient way.
