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Where Can I Find Mold Growth?

mold growth

Mold is an essential part of the natural world. It plays a crucial role in the decomposition process of organic materials.  Mold spores can be found floating around in the air both outdoors and indoors. For most property owners, mold growth becomes a concern when it is visibly growing on a surface inside of their home. However, there seems to be a lot of confusion about where mold can grow. This blog post will talk about the different areas and materials where mold is commonly found indoors. 

Nutrients for Mold Growth

Because mold is a living organism, it needs nutrients to survive. When mold spores land on a surface, they will be inactive unless there are nutrients and adequate moisture present. Fungi, including molds, generally feed on carbohydrates, proteins, and lipids 1.  The surface the mold spore lands on is important because some materials can harbor mold growth while others cannot. Each mold type is equipped with specific enzymes that can be used on specific organic surfaces. Porous building materials that contain a lot of carbon are particularly susceptible to mold growth. Some examples are paper-faced drywall, plywood, wood framing, and ceiling tiles. Non-porous inorganic materials such as sheet metal, brick, or concrete cannot provide the necessary nutrients for mold to grow. However, mold can feed on organic dust or debris that settles on any inorganic surface.

Moisture Causes Mold Growth

Mold also needs moisture to grow. Plumbing leaks, water intrusion from windows, slow leaks from refrigerators, and seepage in the basement are all common examples of potential moisture sources inside of a home. Something many property owners fail to think about is relative humidity. High relative humidity can also cause mold growth.  It is worth mentioning that different mold types can grow at different relative humidity levels. There are primary mold colonizers that are often xerophilic, which means they do not require a lot of moisture relatively speaking. Examples include Aspergillus candidus and Wallemia sebi.  An intermediate relative humidity level between 80%-90% provides adequate moisture for most secondary colonizers to grow 2. A few examples of secondary colonizers are Aspergillus flavus and Cladosporium cladosporioides. When there are high relative humidity levels or liquid water present, tertiary colonizers appear. These include some toxigenic mold types such as Stachybotrys chartarum.

Common Areas

To find mold inside of a home, think about the necessary components that enable mold to grow: places with adequate nutrients and moisture.  There is a common misconception that mold only grows in the dark. This is not true. To find mold, look around plumbing penetrations, on the ceiling, and in the basement for potential leaks or discoloration. Note any water stains around windows or ceilings and measure the relative humidity in different areas of your home. If you have a front-loading washing machine, look inside the rubber gasket for discoloration; I commonly find that a musty odor in a laundry room can be attributed to mold growth inside the gasket. To prevent mold from collecting inside of the rubber gasket, periodically wipe the gasket to remove dirt or debris and maintain the door open as much as possible to dry it out. 


Mold spores are natural and are floating in the air in all environments.  This means that mold growth is possible in all environments with adequate nutrients and moisture. Because nutrients are everywhere, the best place to find mold growth is in areas that are damp. 

To prevent mold inside of your home, the goal is not to remove all the nutrients — remember even dust can be a good source. Rather, keep building materials dry and relative humidity low. Consider having your home inspected for potential moisture problems and mold growth

  1. Elsevier Science & Technology. (2017). Performance of Bio-based Building Materials. s.l. doi: https://doi.org/10.1016/C2015-0-04364-7
  2. Elsevier Science & Technology. (2017). Performance of Bio-based Building Materials. s.l. doi: https://doi.org/10.1016/C2015-0-04364-7

Ian Cull

Ian Cull is a nationally recognized expert in the field of indoor air quality. He is the Chief Science Officer of Indoor Science, a company he started in 2004. He speaks around the world on air quality topics and is a training provider of the Indoor Air Quality Association. Mr. Cull is a Licensed Professional Engineer (PE) and Certified Industrial Hygienist (CIH). His degree is in Environmental Engineering from the University of Illinois - Urbana Champaign. Mr. Cull has developed 50 air quality related courses for the IAQA University and is the author of the book, “Fundamentals of Mold Remediation”. In his words… “Besides being passionate about indoor air quality, I enjoy cycling, music, the Chicago Bulls, and having fun with my three kids.”