New window - mold after window swap

New windows should reduce drafts and the cost of heating bill equally. However, many residents suddenly find mold in the apartment some time after the window swap. In the vast majority of cases, however, this is actually due to the user behavior on airing, which was not changed when the windows were swapped.

Airtight renovation

Often the windows are replaced at the same time, when the facade is renovated. As a result, the whole house is hermetically sealed, which is unusual for the previous residents. Due to their airtightness, they must change their ventilation behavior completely. Otherwise damage caused by moisture and mildew are inevitable after a window replacement.

Shock ventilation - at the right time

Especially in the wet rooms, such as bathroom or kitchen but also in the bedroom should be thoroughly and carefully aired. That may be a contradiction in terms, but it is more carefully meant that you should only air at certain times of the day.

As a rule of thumb, you can always breathe out when it's colder outside than inside. While formerly shying away too much cold air in the rooms, you should now rather keep the temperatures in mind. The warmer the air, the more moisture it contains, so in summer you should only open the windows in the evening or at night.

  • ventilate at low outdoor temperatures
  • make a short draft - five minutes are enough
  • Ventilate at least twice a day
  • no tilted windows
  • no permanent ventilation


Before you push all the damage caused by moisture on the wrong ventilation, you should check whether the window connections were made properly and no cold spots could arise here. Frequently, the residents are first charged before a construction error is considered.

Tips & Tricks

Many landlords are forcing your tenants to air. In any case, they are obliged to inform the tenants about the new rules. For this purpose, simple Fensterfalzlüfter be used in the new window, which produce a kind of forced ventilation. This is intended to permanently eradicate the mold danger that otherwise results from the new windows. This could also be a solution in-house if the windows were replaced to support the change in ventilation habits.

Video Board: VELUX roof window – replacement of pane (glazing unit)