Texas Tech University

What is Growing on my Windowsill?

By Matt Roe

Molds can be found growing everywhere and are present within and on just about every material, including wood, paper, carpet and even food. The spores that molds generate become airborne and are present at some levels in nearly all air that we breathe, indoor and out.

Indoor mold growth that is visible to the naked eye is usually the result of moisture buildup inside of the building envelope from sources such as leaking pipes or condensation from humid air on a cold surface. While mold growth, mold spores and mildew growth inside of a building is a pollutant, it also is naturally occurring and common (Centers for Disease Control and Prevention, 2012).

Typical health effects from exposure to mold can cause symptoms, such as nasal stuffiness, eye irritation, wheezing or skin irritation, in individuals who are sensitive (Centers for Disease Control and Prevention, 2012). More serious health effects, such as shortness of breath, pneumonitis and chronic infections, may occur in individuals with preexisting conditions, such as asthma, chronic lung illnesses and mold hypersensitivity, but this is less common (Centers for Disease Control and Prevention, 2012).

The key to mitigating mold growth inside of a building is removing any obvious growing mold and controlling the source of the moisture within the building. By removing the moisture you remove the opportunity for mold growth. Generally it is recommended that water leaks be fixed and water removed within 24 hours, and indoor relative humidity be maintained below 60 percent (Environmental Protection Agency, 2008). Also remember that as the air temperature decreases, so does the ability of air to hold water vapor. So as exterior windows and walls get colder with the winter weather, they can create condensation points where any indoor humidity condenses on the cold surface.

It also is important to maintain good air circulation in your indoor environment. This includes making sure that at least 10 percent of fresh air is properly filtered and introduced into recirculated air from the indoor space to create air turnover (American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., 2013). By taking these steps to manage moisture and air quality indoors, you can help stop mold growth in indoor spaces.

American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (2013). Ventilation for Acceptable Indoor Air Quality. Atlanta, GA.
Centers for Disease Control and Prevention. (2012). Molds in the Environment.
Environmental Protection Agency. (2008). Mold Remediation in Schools and Commercial Buildings.

Matt Roe is an environmental safety manager in the Office of Environmental Health and Safety.