In this week’s article, we address one of the most common problems within a building: humidity.
The topic is vast and complex, as understanding the causes and consequences is not a trivial or simple task. At the same time, however, it’s important to understand its origins and know how to address them, as humidity is synonymous with other, more complex problems such as condensation and mold, and, indirectly, pathologies and illnesses.
What is humidity and what causes it?
First, let’s define humidity: it’s the amount of water vapor present in the atmosphere, in a substance, or in a body. Humidity is always present inside buildings: in the air, on the surfaces of objects, and in the composition of building materials.
There are two types of humidity: relative and absolute, which depend on two other factors: temperature and saturation humidity. The former, which requires no clarification, refers to the temperature of the air, while the latter indicates the maximum amount of vapor that can be contained within the air before it turns into water. These two factors are closely related, as the amount of water vapor also varies as the temperature varies.
What are the consequences of humidity in buildings?
Having briefly outlined what humidity is and its forms, we can now focus on the main consequences it can cause in construction.
The three main consequences are: structural deterioration, mold formation, and condensation.
Deterioration of building structures
The presence of water on building surfaces, whether external or internal, and within building components, is the cause of many types of deterioration. The deterioration of building components is almost never a direct consequence of humidity, which is why we can distinguish between direct and indirect consequences.
Direct consequences
Direct consequences include all those phenomena visible to the naked eye:
Impregnation, especially in porous materials;
Abrasion, dissolution, and leaching, in porous materials, plaster, and paint;
Fracture, also due to hydrostatic pressure, present in concrete, stone, brick, and flooring;
Corrosion, for example, in metals.
Indirect consequences
These represent all those visible and invisible phenomena that result from the presence of water. These include:
Reduced mechanical properties of materials, such as resistance,
Reduced insulating capacity,
Deterioration due to the action of biological agents, such as mold, algae, and plants.
Conditions that favor the growth of mold
Among the most common visible consequences is mold. Mold is simply a fungus that doesn’t perform photosynthesis, meaning it doesn’t require direct light to survive, especially to reproduce. In fact, it’s found primarily in shaded and humid areas. Even if we can’t see it, mold, in spore form, is present in the air we breathe. It transforms into visible mold when there’s a combination of available surface area and ambient humidity above 80%. This is why it’s important to keep humidity levels low in the air and on surfaces.
Consequences on materials and human health
Mold growth is dangerous both for the materials on which it grows, as it releases acids that dissolve the substrate to survive and reproduce. It is also very harmful to human health. It produces so-called “mycotoxins,” which can cause the following reactions in humans: allergies, irritation, and infections.
Surface condensation and interstitial condensation
Condensation is simply the phenomenon that causes water vapor in the air to solidify. Furthermore, this phenomenon occurs when the percentage of water vapor exceeds a certain level. Within homes, this phenomenon occurs when air comes into contact with a cold surface, such as uninsulated perimeter walls or thermal bridges.
Condensation itself is not dangerous, but its consequences are dangerous: primarily the formation of mold and the deterioration of building elements.
We can therefore identify two different types of condensation: surface and interstitial.
Surface condensation, as the name suggests, is the type that forms on the surfaces of objects. We typically find it on windows and bathroom mirrors after showering.
The second type, interstitial condensation, occurs within porous materials, which, upon contact with moisture, allow it to penetrate. This phenomenon leads to a typical characteristic of building structures: transpiration, which, if not properly controlled, leads to an unhealthy environment. This type of condensation is particularly harmful to insulation: in the presence of water, it tends to degrade very quickly and irreparably.
Thermal Bridges
I mentioned thermal bridges earlier. They occur in areas adjacent to the exterior that are not properly insulated and contain materials with different thermohygrometric characteristics. They occur on beams and pillars in exterior walls, which have little or no insulating capacity.
Tips for a damp-free building
Since moisture accumulation is essentially a winter problem, the most effective way to avoid problems is to ventilate the rooms.
Other solutions include mechanical systems, such as controlled mechanical ventilation, which extracts stale air from the interior and introduces clean air from the outside.
Other possible measures to prevent mold and humidity include the use of external insulation, paints with nanotechnology that help maintain a slightly higher temperature inside the building