It is particularly annoying if moisture intrudes into newly installed building elements. This is often blamed on the new window and having to replace it is viewed critically. But accumulating moisture in and around the window can also be seen as an indicator: There is too much moisture in the flat/house. A much better indicator, however, is a hygrometer, which always displays the current level of humidity to the occupants of the flat. These should be set up especially in rooms where a high humidity load can be expected - for example, in bedrooms. For human well-being, the air humidity in living spaces should ideally be between 40 and 60 per cent.
Changes in living conditions and construction methods influence ventilation cycles and humidity loads. Here are some Examples:
- Leaving the flat/house in the morning and not using it again until late in the afternoon.
- Drying laundry in the living- or bedrooms.
- Flow conditions in the room have changed dramatically due to low-temperature and radiant heating.
- Making the kitchen part of the living space.
How tight is airtight?
Window constructions have all been optimised so that they can now withstand the more difficult prevailing climatic conditions. But there is a risk that the casing is too exposed to moisture or that moisture seeps through the smallest micro-openings in the window construction; after all, even today there are no absolutely airtight windows. Furthermore, the positive pressure prevailing in more airtight buildings causes the humid inside air to be pressed through the smallest gaps at the window. If the temperature in the cooler areas of the profiles falls below the dew point, the moisture condensates. Since thermal lift in an open space always leads to higher pressure at the top, windows on the upper floors are therefore more affected than elements on the lower floors. And the more airtight a building is, the stronger this effect can be observed. Thus the problems always start on the upper floors.
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As serious as the problem of ventilation is, the solution can be simple: a well-adjusted ventilation system that does not generate positive but rather slightly negative pressure.
The rate of exchange of the air is decisive
However, if no central or decentralised ventilation systems are in use, it is necessary to control the indoor air loads on the user side and to ensure sufficient moisture transport from the inside to the outside with a sufficient rate of air exchange. If this air exchange rate is not provided, this is at the expense of both healthy indoor air quality and an increased risk of moisture damage in the dwelling.
Risk recognised, risk averted?
As a rule, it is no longer sufficient to install new windows and tell the tenant or owner to ventilate regularly: DIN 1946-6 specifies requirement for minimum air exchange in such a way that user-independent ventilation must be ensured for every new building and every modernisation measure in which more than one third of the existing windows are replaced. The responsibility for this lies with the planner, i.e. the architect, the contractor or - if the planner is not available - the executing company.
What does this mean?
First of all, it is necessary to verify whether the user-independent minimum air exchange occurs automatically via the natural infiltration through the building envelope or whether the planner must secure this with ventilation measures. If measures are required to ensure the user-independent minimum air exchange, it must be ensured for moisture protection that the room air is completely exchanged once every six hours without tenants or owners intervening themselves. If the party responsible does not comply with this obligation, they can be held liable for moisture damage that occurs later.
How to ventilate properly:
"In general, the rule should be: Quick and hard. This prevents the house and flat from cooling down and also significantly reduces the risk of unwanted visitors," says Frank Lange, Managing Director of the Verband Fenster + Fassade (VFF).
Tilting windows is particularly popular. But: this has the particularly disadvantageous effect that the rooms then cool down permanently. Quite apart from that, tilted windows are also an invitation to burglars.
Speaking of ventilation: Here is an almost invisible new ventilation flap
It is better to open the windows in the house or flat on opposite sides or on different floors (thereby creating a drought) - then the air is exchanged in the shortest possible time. As a rule of thumb, 5 minutes should be enough to exchange all the air in the room. This process should be repeated at least three times a day. Even so, little basic heat is lost, because the floors, cabinets and walls stay warm.
