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The Home Depot

Why Are My Windows Moldy?

Pro Referral > Home Guides > Door & Window > Why Are My Windows Moldy?
Why Are My Windows Moldy?

Home owners typically spot mold on windows when they open them in spring after keeping them shut all winter. Mold on windows is visible as black mold. This can spread to other parts of the house and cause extensive damage. This can lead to additional remediation expenses as well. Besides, the mold spores can enter the home and cause health problems such as allergies and asthma in many people.


The best way to prevent all of these problems is to prevent the growth of mold in the windows. This can be done by understanding the cause of the growth of mold. Once you are aware of what causes the mold to grow on the windows you will be able to take steps to prevent its recurrence.

  1. 1.Window Sill

    Window sills in most houses are either made of wood or aluminum. While mold requires the presence of organic matter and humidity to grow, it is quite frequently found on both wood and aluminum window sills. This is because the mold uses the organic matter present in household dust for sustenance. In the case of aluminum sills, the mold grows when dust settles on it and there is sufficient moisture as well. In the case of wooden sills, the mold can grow on the wood substrate as well. In order to prevent this, you can paint the wooden sills using a high gloss paint that protects the wood.

  2. 2.Glass

    The glass panes of windows are not organic and should not cause the formation of mold. However, if the glass panes have not been dusted and have accumulated organic matter in the dust, it can lead to the growth of mold. Additionally, if moisture is trapped between the double panes of a window, this can help in the growth of mold.


    Moisture is collected between the glass panes of a double paned window or on the indoor side of a window pane because the warm air indoors is cooled when it comes into contact with the cooler window panes. This causes condensation. One can prevent the formation of mold on window panes by wiping dry the glass panes. Keeping the glass panes of the window dust free or moisture free will help prevent the growth of mold. Additionally, you can also reduce the condensation on the window panes by reducing the humidity indoors by setting a lower level in the humidifier.


    There is another incentive to keeping your windows clean and it is security. If your windows are dirty you will have trouble seeing outside if someone is trying to sneak up on your home or a neighbor’s house. Protecting your neighbor’s home is no different than protecting your own. With clean windows, you can see your family or whoever is outside better and you can also keep a closer eye on your pets.

  3. 3.Frame

    Window frames are typically either made of aluminum or wood. Both these frames can develop mold when the conditions are right. In the case of aluminum frames, indoor dust that is rich in organic matter can accumulate in the joint where the glass meets the frame. Furthermore, this joint can trap the condensation that occurs near the windows, ensuring optimum conditions for the growth of mold.


    In the case of wood frames, the moisture trapped near the joints of the wood and glass is enough to encourage the growth of mold as the wood is the organic substrate that provides the food for the mold. In order to prevent the growth of mold, one needs to ensure that the joint between the wood and glass is free of dust and moisture. This can be done by scheduling weekly cleaning of these parts of the window.

  4. 4.Tracks

    Modern window systems frequently have aluminum tracks that help to slide the glass panes of windows open and shut. However, these tracks can also accumulate dust and moisture more easily and can be difficult to clean manually. The accumulated dust and moisture leads to the growth of mold. In order to ensure that the tracks of the window are free of dust, they should be vacuumed once a week and after using a brush to dislodge the dust.


    Many window tracks have small holes to enable the water to drain out of them. However, these holes can become blocked with dust unless the tracks are cleaned regularly. If you find mold in the window tracks, you need to first remove the mold before cleaning the holes and then dust off the tracks.


    In many cases, mold on windows is not a major problem and home owners can clean the mold using a mild detergent before wiping the windows clean. To prevent a further recurrence of mold on the windows you need to include weekly window dusting as part of your housekeeping routine. Additionally, you can reduce the humidity levels inside your home by resetting the humidifier and moving out any indoor plants.


    However, sometimes, the mold can have spread to the sheetrock under the windowsill. In such cases, you need to retain the services of a mold remediation expert who will ensure that all traces of mold are removed from the structure. Additionally, if the sheetrock is extensively damaged, it might have to be replaced to ensure the safety of the structure.

The presence of mold in your windows is unsightly and can cause health problems. However, it is possible to get rid of the mold by using a mild detergent and prevent its recurrence by scheduling regular cleaning of windows. If the mold has spread to the sheet rock, it is advisable to use mold remediation services to ensure that it does not spread any further.


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