Have you ever seen a house breathe? Probably not!

Let’s start with the concept that there are no materials that “breathe” but rather “transpire,” meaning they have the ability to allow the passage and absorption of a certain amount of water vapor and release it under certain circumstances. These materials make indoor spaces healthier, reduce the risk of condensation and mold formation, all within certain limits defined by the characteristics of the materials themselves, in combination with the type of load-bearing masonry, temperature, and air circulation.

Let’s begin with the last point: the ventilation of indoor spaces is the only way to achieve the essential air exchange in our environments. This can be done by opening windows or through a more technological method, mechanical forced ventilation. In the former case, which is commonly used alongside stale air, opening windows leads to a significant loss of energy spent on heating or cooling the indoor environment, making an investment in a mechanical ventilation system a viable option. Such a system provides constant fresh air exchange with humidity and temperature control.

It often happens that replacing old windows with more airtight ones can lead to increased mold formation since the new sealed windows won’t allow for natural air exchange (involuntary).

The presence of humans and their activities indoors generates a considerable amount of water vapor, especially in bathrooms and kitchens. In the case of an old house with lime or gypsum plaster, and old wooden windows with drafts, mold is unlikely to form because a significant amount of vapor escapes through the windows, and some is absorbed by the lime plaster. This mechanism allows for humidity regulation, especially when considering the past practice of vigorously heating with wood. Thinking that water vapor can pass through walls is a significant misconception; only a very small portion of it manages to escape through the walls, while 99% is exchanged through open windows.

Let’s debunk the second notion that a thermal insulation system (external insulation system) prevents a house from “breathing.” As mentioned earlier, a house has a certain degree of transpiration depending on the materials used. For example, in the case of an external thermal insulation system (EPS with acrylic finish), there’s minimal to no transpiration. However, this is not a problem; the significant advantage is that by eliminating all thermal bridges (the highways of cold), you increase the temperature of the walls, reducing their criticality and eliminating condensation and the subsequent formation of mold. It’s clear that by applying thermal insulation and properly ventilating the rooms, in almost all cases, mold-related problems can be resolved.

To draw a metaphor, if we imagine our house as our body, the exchange of air between the interior and exterior mostly happens through breathing air into our lungs through the oral cavities, which can be likened to the windows of the house. If we think that by wearing a raincoat we can’t breathe anymore, you can see the error. We need to breathe through the windows or through mechanical ventilation (nose and mouth) and wear breathable materials that allow our skin not to condense and keep us warm.