Mold on Windows

Q: I found black spots that look like mold around the edges of my windows. Could these be harmful? What should I do?

A: Mold spores are around us all the time floating in the air, but mold becomes troublesome when it is visible and grows in cool, damp parts of the home, such as shower curtains, near plumbing leaks, damp laundry, bathroom ceilings and single-pane windows.

Each person’s health tolerance of mold is different. People who are sensitive can experience nasal stuffiness, eye or skin irritation, or wheezing. Others, such as those with serious allergies, may have more severe reactions like fever and shortness of breath. Consider talking with your health care provider and reviewing literature from the Centers for Disease Control and Prevention to learn more.

Single-pane windows, which consist of a single sheet of glass, can form condensation on the interior side when outdoor temperatures are chilly and inside temperatures are warm. If the condensation isn’t wiped or dried quickly, mold starts to grow because the window frame consists of mold food: wood. Some residences avoid this by using metal-framed single-pane windows.

The best way to control mold is to control the moisture from window condensation. Try the following strategies (ordered from lowest to highest cost):

  • Perform routine maintenance.
    • Keep drapes and blinds open to help speed up drying time and decrease the opportunity for mold growth.
    • Monitor windows for condensation and wipe it away as soon as possible.
    • Wipe away mold or discolorations with a damp soapy rag when needed.
  • Install exterior or interior storm windows to minimize condensation. Storm windows must be closed to truly help. Checking for and wiping away condensation will still be needed, but not as often as for windows without storm windows.
  • Replace single-pane windows with double-pane windows to eliminate cold windows and condensation.

Adding storm windows or installing double-pane windows can be costly despite the likely benefits of less maintenance, improved comfort, fewer pests and lower energy bills. Thankfully, double-pane windows have been required by the North Carolina Building Code for decades.