Do you know where the humidity comes from when it appears at home?

Concept of humidity

Steam is water in gaseous state. The term humidity refers to the amount of vapor present in the air. This is defined as saturated air, when it remains in equilibrium in the presence of liquid water without any transfer occurring between the two. The partial pressure of the water vapor contained in this air is called saturation pressure (Ps), and there corresponds a specific value for each temperature. Absolute humidity is the weight of vapor contained per unit of air, kg/m3, or also the weight of vapor per unit of dry air weight. On the other hand, relative humidity (Z) is the ratio between the weight of water vapor contained in a volume of air and the weight of saturated vapor of the same volume. Z (%) = (Weight of vapor/Weight of saturated vapor) x 100

 

The dew point is the temperature at which the water vapor contained in a mass of air becomes saturated vapor due to a decrease in temperature. When this vapor content is excessive, it condenses on the cold surfaces of a house, whether in walls, enclosing walls, or windows.

Origin of humidity when it appears inside a house

Therefore, humidity is always present in our home, but certain pathologies or construction defects cause its condensation. When humidity results from the previous process, it is called condensation humidity. It usually manifests in points of the facade enclosure due to a deficient level of thermal insulation and inadequate ventilation of the interior spaces. Energy rehabilitations have one of their goals to prevent this type of humidity from manifesting within homes. When humidity comes from rainwater, we are faced with a filtration humidity, whose origin needs to be sought in other kinds of pathologies such as lack of waterproofing in unique elements of the building: the junction between the slabs and the facade enclosure, or the covering materials of the roof.

Hygroscopic materials

Another factor that significantly affects the presence of humidity is the hygroscopic behavior of the materials that make up the envelope and furnishings. This property allows them to exchange humidity with the indoor air. Therefore, hygroscopic materials are those capable of absorbing a significant amount of moisture from the surrounding air. These materials allow for the buffering of humidity fluctuations through that exchange between the humidity of the environment and the moisture that the building envelope can hold. They are porous materials that can reduce interior humidity levels and therefore improve comfort and air quality in homes. This also reduces their energy consumption.

In reality, all construction materials are porous. The pore volume ranges from 0.5% of the gross volume in the case of granite to 95% in mineral wool. This porous structure in hygroscopic materials allows water to adhere to the solid surface of the material when the water vapor has not yet reached saturation levels. This is how the material's capacity to store moisture increases.