We are happy to share with you our knowledge and expertise in housing development. Keep up with the latest news by reading our articles.


Technical condition of buildings and common defects – humidity

13. October 2020 | Ing. Lukáš Lucký

Falling plaster, floor cupping, damp stains, mold on the walls or floors – sounds familiar? All the above phenomena have one common denominator – water (increased indoor humidity). The issue of humidity in interiors and structures is addressed by the building physics. When designing new buildings and renovating older ones, building physics is a discipline no builder can do without. The aim is to ensure the building is sound from a thermal and acoustic point of view. Detailed dynamic hygrothermal simulations and calculations of critical building structures eliminate any future possible risks and defects of structures. For existing buildings, dynamic hygrothermal simulations may help identify critical points and propose suitable remediation measures.

Modern computers were not around when buildings were built in the 1950s, nor was there such an emphasis placed on the indoor climate, the thermal and acoustic properties of the materials used and the energy efficiency of the buildings. Perimeter walls were made of masonry, reinforced concrete or prefabricated panels. Only rarely we see thermal insulation of perimeter walls in older buildings. The windows of these buildings are usually reclassified as having weak thermal insulation properties. In the winter, the radiators must run at full capacity to ensure thermal comfort in the building. The common issues in these older buildings are the leakage of the perimeter wall and the weak thermal insulation properties of the materials used.

What causes mold and dew on windows?

There are three factors which cause mold on the inside of the perimeter walls and dew on the windows: air temperature (indoor and outdoor temperature), relative humidity (relative indoor and relative outdoor humidity) and dew point temperature. The term relative humidity means that the volume of water vapor contained in the air is conditioned by the ambient temperature. Simply put, warm air at relative humidity, e.g. 50% contains a larger volume of water than cold air at the same relative humidity. The air volume of 1m3 at 20 ° C can hold up to 17.3g of water. If the air temperature drops to 5 ° C, for example, the air will contain only 5.3 g of water. Dew point temperature is the temperature at which the water vapor contained in the indoor air begins to condense on the surface of the structure.

When designing a building, the aim is to design the building structure so as to prevent the formation of mold on the surface of the structures. Calculations are based on boundary conditions – the temperature and relative humidity in the assessed space. For the living space, an internal temperature of 20 ° C and a relative humidity of 50% are considered optimal. The recommended relative humidity in the living space is between 40% – 60%. If the relative humidity falls below 40%, it entails serious health risks such as drying of the mucous membranes of eyes, nose or throat, which weakens the body’s defenses against disease. If the humidity is above 70%, the risk of mold growth increases. Let’s have a look at the model situation – if the ambient temperature is 20 ° C and relative humidity 50%, then the dew point temperature is 9.26 ° C. If the surface temperature drops to 9.26 ° C or below 9.26 ° C, water begins to precipitate on the surface of the structure and form wet spots. Therefore, walls, ceilings and floors must have a surface temperature above 9.26 ° C. Another important indicator when assessing structures is a safe surface temperature. The safe surface temperature is based on the critical surface temperature for mold formation. At the above-mentioned boundary conditions of a temperature of 20 ° C and a relative humidity of 50% inside, the safe surface temperature is 13.12 ° C.

When do molds form in the interior?

Once the peripheral structure reaches the safe surface temperature of min. 13.12 ° C, there is no danger of mold formation in the interior. When the structure is cooled below this temperature, mold start to form on the walls, ceilings and floors. Mold can be removed by increasing the interior temperature, decreasing the relative humidity or increasing the thermal resistance of the structure by means of exterior insulation of the peripheral structures. Exterior thermal insulation of the building is a great way to prevent mold formation and increase the surface temperature of peripheral structures. In the case of cultural monuments, where intervention into the facade is not permitted, insulation might be done from the inside. Once the decision to insulate the building from the inside is taken, a lot of issues arise which must be assessed separately, especially during the perimeter structure design phase. The implementation itself is more complicated and expensive compared to external insulation.

Falling plaster from walls as the effect of moisture?

When repairing surfaces damaged by moisture or water, it is first necessary to determine the cause of moisture. The most common causes include: leaking water pipes, sewers, water rising from foundations, damaged or absent waterproofing layer of floors and walls, moisture absorption through the plinth of the building, condensation of water on the surface of structures. Some faults and defects are easy to remove, however, some are pretty difficult are require a more detailed analysis by a qualified person and comprehensive solution, such as adding a waterproofing layer under the perimeter masonry to prevent water from rising from the subsoil.

Dew on windows is a common phenomenon in older insulated buildings. When insulating the perimeter cladding, it is recommended to replace the original windows with ones having thermal insulation properties according to current standards. In principle, the lower the heat transfer coefficient of a window (known as the Uw value), the better the thermal insulation properties. The thermal insulation properties of windows are affected by the thermal insulation properties of the glazing and the window frame. Windows with thermal insulation triple glazing meet today’s standards and norms. The choice of the frame material (wood, plastic, aluminum, or a combination thereof) is a matter better left to the architect or the client himself. External insulation makes the building tighter and eliminates heat loss. Air no longer flows at the original intensity through the perimeter walls and joints. The indoor humidity increases – it must be regularly regulated by natural ventilation or by forced ventilation through air handling units. In the absence of forced ventilation, natural ventilation is recommended (through windows). The best way to ventilate the rooms is to open the windows and doors wide for a few minutes. In case of excessive interior humidity open the window and select a tilt position so that there is no draft in the room (the interior temperature should not drop below certain level) and the air exchange is ensured. We recommend using a hygrometer to monitor indoor humidity. As the interior humidity increases, the required safe surface temperature of the structure also increases. As mentioned, at a temperature of 20 ° C and a relative humidity of 50%, the water vapor contained in the air begins to condense at a temperature of 9.26 ° C. When the relative humidity is increased to 60%, water vapor begins to condense on the surface at a temperature of 11.73 ° C. With insulating double glazing, it is difficult to reach this temperature in winter. For this reason, condensation forms on the window frames and glazing during the winter.

Floor cupping as the effect of moisture?

After being exposed to moisture, floors tend to change their properties, cup and change shape. As with walls, moisture can enter the floor structure from damaged water distribution, sewerage, heating in the floor, broken or the absent waterproofing layer. Through the damaged part of the waterproofing, water starts to seep into the structure and negatively affects the floor, including its upper layer, which slowly deteriorates and deforms due to moisture present. Replenishment of the floor waterproofing layer is an extensive process that requires the removal of the original floor to the ground level or even foundation.

How to eliminate these defects?

Increased humidity in the interior and consequences it entails are not only a problem of older buildings but newer ones too. Some buildings were built at a time when the energy efficiency of buildings was not a thing. Restoration of the building requires a professional approach and a detailed analysis of the existing condition of the building by a qualified person. Based on the obtained information and samples taken from the examined object, an expert will draw up a restoration project. It should be borne in mind that individual defects influence each other and, sometimes, make other conditions even worse. When inspecting the building and drawing up the restoration project, it is necessary to focus on the building as a whole and not only on defects themselves. It is also important to eliminate the causes of defects and come up with a comprehensive renovation plan. The price for renovation works depends directly on the scope of the renovation. We always recommend to acquaint the project designer with the scope of works you have in mind so that pricing can be done right.


cross Thank you for your message. We will contact you.
Let us
stay in touch

Check out our social network profiles, too. You will learn interesting facts about us, our projects and also be updated on news from the world of project development and architecture.

Send us
a message

    * required