July 29, 2026, 1:19 pm | Read time: 3 minutes
A well-maintained facade makes a good first impression. However, unsightly black spots or streaks can form over windows over time. The good news: They can often be prevented, as they are usually caused by improper ventilation habits.
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Not Paint, but Algae, Moss, and Mold
Black spots on the facade above windows are a common problem. Sometimes it’s just a light gray haze. In other cases, it’s a noticeably black area. The discolorations on the house facade above the windows strongly resemble mold spots that can form inside a building. Not without reason: They are actually deposits of algae, moss, and mold fungi.
Improper Ventilation Leads to Black Spots Above the Window
It’s noticeable that the black spots on the facade form particularly above windows. Why is that? The mold and mildew spots are related to the habits of the people living behind the windows. In many cases, the deposits can be traced back to improper ventilation. Although many windows have a tilt function that many find convenient, it’s better to open the window wide for ventilation. Those who ventilate exclusively or predominantly with a tilted window must expect black spots on the facade above the window.
The warm and humid indoor air rises through the tilted window and hits the colder wall area above the window. Due to the temperature difference, the air condenses there. The condensation is the ideal foundation for moss, algae, and mold fungi to settle–just like on the window when condensation forms there. Facades with thermal insulation are particularly susceptible to this damage pattern because they minimize the heat flow from the building. Therefore, the facades are colder.
Also interesting: Prevent mold with the right building materials
Leaving Windows Ajar? Why That’s Not a Good Idea
What Happens in Your Home When You Ventilate Too Much
How Can You Remove the Black Spots?
Since the black spots on the facade above windows are a biological contamination, you don’t need to paint the house immediately. If the spots are at heights you can reach with a ladder, you can remove the mold deposits with vinegar, baking soda, or soap. A pressure washer can also help eliminate the traces.
If larger areas are affected or the spots are stubborn, it’s advisable to hire a professional to clean the facade.
Avoid Black Spots by Ventilating Properly
To prevent the black deposits from reappearing or worsening, you should ensure proper ventilation. Avoid tilt ventilation. Ventilating with an open window is more suitable. Pay particular attention after cooking or showering.