Top 7 Causes of Mold in Commercial Properties

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Courtesy of Karl & Associates Inc.

Mold growth within commercial buildings is a common concern for building occupants, as it has been linked to a number of health effects and can be found lurking within the walls and within ventilation systems, oftentimes going undetected for long periods of time. Here are the top seven causes of mold in commercial properties and what you need to know to prevent them.

Improper Operation and Maintenance of HVAC Systems

AnHVAC systemthat is in disrepair can be a prime location for mold growth. Excessive moisture within the HVAC system can promote mold growth that is easily circulated throughout the building during normal operation. Within an HVAC system, there are several components that are common contributors to mold growth and should be inspected regularly.

Drain Pans.Drain pans collect condensation from the cooling coils that are used to dehumidify the air. The drain pan should always be sloped properly towards a condensate drain line and cleaned regularly to prevent the accumulation of stagnant water.

Air Filters.Ventilation air filters should be replaced on a regular basis and checked to ensure proper installation. Air filters that are not maintained can become saturated and will encourage microbial growth.

Air Ducts.Excessive moisture in air ducts is usually due to leaks or failure of other HVAC components. It is imperative to check for leaks periodically and make repairs quickly before mold is circulated throughout the HVAC system. Air ducts should also be free of organic debris that will further encourage microbial growth.


Condensationoccurs when moisture in the air comes into contact with cool surfaces, including windows, piping, lavatory fixtures, and even interior walls. Common causes of condensation include excess humidity in the air, lack of circulation, and lack of insulation. There are two methods to control condensation:

  1. Increase the surface temperature in problem areas with increased air flow or insulation around piping and within walls.
  2. Reduce the moisture in the air with an HVAC system. The EPA recommends keeping the relative humidity of a building below 60 percent. Oftentimes, condensation is a sign that the HVAC system is in need of repair.

External Sources

Water vaporandorganic debriscan enter buildings through air intake points often found on rooftops of commercial buildings. Water vapor can create excess loads on the HVAC system, which can lead to failure, and organic material will typically contain mold and fungal spores that can be distributed throughout the building.

Cooling Towers.Cooling towers are typically found on the roof of a commercial building in order to release waste heat to the atmosphere. It is not uncommon for water vapor released from a cooling tower to make its way back into an HVAC system, leading to mold growth within various system components. Mold spores within the cooling tower itself can further exacerbate the problem.

Additional sources of water vapor and organic material can include:

  • Standing rain water
  • Vegetation
  • Refuse
  • Animal waste

Regular building maintenance should include frequent inspection and cleaning on rooftops for standing water, build-up of debris, and other sources of moisture. Cooling towers may require monitoring for water quality and occasional cleaning.

Roof Leaks

Leaky roofs provide a means for moisture to enter a building’s structure where mold can grow slowly and sometimes undetected. Inspection and maintenance should be performedregularlyas well as after extreme weather events. If mold is suspected in a building, the roof should be checked for:

  • Standing water
  • Areas of pooling
  • Bubbles in the roof cover

These may indicate areas of trapped moisture and general wear on the roof cover and joints.

Plumbing Leaks

Leaky plumbing can be a serious concern for commercial buildings. Standing water and wet materials provide ample opportunity for mold to grow. Plumbing systems can include:

Basement flood control systems

  • Kitchen fixtures
  • Bathroom fixtures
  • Fire protection systems
  • Rooftop plumbing for HVAC systems

Additionally, cooling towers should be inspected regularly to ensure that all parts, including the drainage system, are working properly. Damage from cooling tower leaks can be costly and extensive, as they hold large quantities of water and are oftentimes located on rooftops.  All other pipes and fittings should be routinely checked for leaks and replaced immediately when necessary.

Construction Materials

Construction materials are often installed in a wet form. For instance, concrete is poured wet and must be allowed to thoroughly dry before construction can continue. Other materials such as gypsum wallboard and wood flooring may have absorbed moisture from the environment during installation. Special care must be taken to remove moisture from building materials often using a dehumidifier. If building materials are not dried properly, mold may begin to grow within the interior of new buildings or in renovated areas before the construction is even fully completed.

Poor Housekeeping

Mold requires an organic food source in addition to moisture. Sometimes, all that it takes to encourage mold growth is an area full of dirt and debris to provide food for mold spores. Ventilation systems can spread dirt and dust throughout the building encouraging mold growth in areas that are prone to moisture. The best way to maintain a healthy environment is with regular cleaning and maintenance.


The best way to combat mold growth in commercial buildings is through routine maintenance and repair. Here are some guidelines to follow:

1.       Check all components of an HVAC system regularly and change filters as scheduled.

2.       Adjust the HVAC system if excessive condensation is forming on windows or around piping.

3.       Perform building maintenance as scheduled and after storm events, particularly looking for water, debris, and damage on the rooftop.

4.       Check plumbing fixtures regularly, and repair leaks immediately.

5.       Maintain a clean indoor environment.

6.       Immediately investigate any reports of musty or moldy smells or sickness from building occupants.

If you notice any potential signs of mold, you should consider bringing in a mold inspector to look for core signs of mold and to provide ways of prevention and cleaning.

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