No one should think that black mold only grows on basement walls or dark crawl spaces. Black mold, Stachybotrys chartarum, can grow anywhere that suitable conditions are present, including windows.
It would be an assumption to conclude that black mold would grow most in geographical areas of high humidity. That isn’t the case at all, and a number of states identified as having the highest reported claims of mold hazard by the American Risk Management Resources are not exactly tropical (e.g. Arizona and South Dakota are on the list). Windows may find themselves covered in mold, not because of the humidity outside, but because of the humidity inside the building.
The humidity needed for the production and growth of black mold is a relative humidity rate (RH) of fifty five percent or more. That would make the windows in a bathroom highly susceptible. A fan in the bathroom can quickly dry up any moisture left after a bath can reduce the RH level as well. Moisture can, however, intrude from the outside and collect on a window’s ledge. This is particularly likely to happen if the window is directly underneath a faulty gutter or rainspout. An immediate remedy is to put a strong sealant around the edges of the window, making the window itself airtight.
Another means would be to fix the gutters, as gutters may cause moisture to seep into the house by other means if left unattended. Even though the windows are airtight, however, there is still a possibility for black mold to grow. Single glazed windows and metal window frames, known as “crying windows”, create a potential problem when the humidity inside is high and the weather outside is cold. Condensation can form and resultant dampness is a breeding area for mold. Fortunately, in most cases this condensation will evaporate once the temperature outside rises.
Moisture can collect on windows from other sources as well. It has been mentioned that a fan can dry up collected moisture, but the ventilation system in the house may itself be a serious problem. Water can collect in the ducts of a ventilation system and become a breeding ground for black mold. Once the spores have been generated, the fans of the system could then actually blow the spores out into the atmosphere and gather on the window sills to propagate there.
Preventive measures can reduce the chances of black mold forming in window areas. Metal or wood blinds ought to be kept open when the outside temperatures are low, and replacing them with porous materials that let in the sun’s rays is a good idea. Perhaps the best solution is good circulation of air from fans that have themselves been first examined for residue mold or moisture. These fans need to be run immediately after bathing for maximum effect. Routine inspection of the caulking around the windows can detect any potential moisture problems and if weep holes are a part of the window construction, these should be looked at to make sure that no debris has clogged the holes. If any moisture is noticed on the windows, it needs to be wiped off as soon as possible. De-humidifiers might also be used to keep humidity at proper levels.
In essence, routine maintenance can keep a window and its surrounding area free of mold generating moisture. It doesn’t take much time or effort, but a routine inspection of the windows can prevent a potential mold hazard from developing.