INTRODUCTION AND BACKGROUND: Molds can adversely impact peoples’ health, and cause physical damage to infrastructure, resulting in considerable negative impact on the global economy. Exposure to molds in work and residential environments can cause a variety of adverse health effects, including asthma and allergic reactions. The World Health Organization’s (WHO) 2009 Guidelines for Indoor Air Quality: Dampness and Mould1 reports that, “indoor air pollution – such as from dampness and ‘mould’, chemicals and other biological agents – is a major cause of morbidity and mortality worldwide,” and that “microbial pollution is a key element of indoor air pollution1.”

The Environmental Protection Agency (EPA) reports “the public health risk of asthma from dampness and mold was estimated at 21% of all asthma cases in the U.S.”, and suggests that risks in public buildings are similar to those from exposures in homes2. As such, approximately 4.6 million cases of asthma are attributable to dampness and mold exposure in the home – causes that can be controlled. The national annual cost of asthma in the home is estimated to be $3.5 billion, including the cost of medical care and the value of lost work and/or school days. Another study suggests that dampness and mold in buildings is a significant public health problem with substantial economic impact, and that there is a need to control moisture in both new and existing construction because of the significant health consequences.

DefinitionMOLD AND ITS NATURE: Molds are fungi (e.g., mildews, puffballs, mushrooms, yeasts), and exist ubiquitously in nature. They are neither plants nor animals, and reproduce through the formation of fine microscopic spores. These spores are extremely light and disperse through air movement. They float through the indoor and outdoor air, and all living beings breathe molds continuously.  All that molds need to grow is moisture and decaying organic matter. Without mold, the world would be overrun by dead plant matter, thus molds are an important part of the environmental ecosystem.  With sufficient moisture, molds can settle on and consume organic construction materials (e.g., wood, drywall, window frames, carpeted or uncarpeted flooring, insulation materials), until the materials are completely consumed, thereby destroying a building’s structural integrity. The most common indoor molds are Cladosporium, Penicillium, Aspergillus, and Alternaria. Some diseases are known to be caused by specific molds, with examples of the toxic molds including members of the Stachybotrys and Aspergillis families.   

WHY MOLDS ARE A PROBLEM:  The $3.5 billion cost noted above refers only to asthma-related health care and human suffering, and does not include expenditure on residential and commercial structural remediation, and the damage to grain stockpiles in agriculture and shipping. In addition, studies have repeatedly demonstrated that dampness and mold in buildings is a significant public health problem with substantial health consequences and economic impact – up to 500 billion dollars by some rough estimates 3.  Thus the health, productivity, and commerce-related costs cause a tremendous strain on the U.S. economy, citizens, and business. These costs and health impacts are sufficient reasons for workplaces and home-owners to identify and prevent unwanted mold.

PREVENTION: Moisture control is the key to prevention of mold growth inside commercial and residential buildings. Better moisture control techniques should be considered and incorporated during building design. Building engineering practices should include plan reviews during the building design phase to ensure that proper moisture control and drainage is called for in the building structure, including grading of the grounds and draining of foundations. Water intrusion pathways should be eliminated and moisture barrier practices adopted during construction.

Other good practices for controlling humidity and moisture include prompt response to water intrusions (e.g., leaks, spills), condensation control, drainage maintenance, lowering atmospheric humidity levels (below 60% preferred), temperature control, improved ventilation levels, and insulation. Timely preventive maintenance, cleaning, and keeping work-areas clutter-free are also good practices.

CONTROLLING MOLD:  Suspected and unwanted mold growth should be quickly identified and assessed   by a professional, by conducting visual evaluation or testing. A remediation plan should be developed to include the removal of the contaminated items, and disposal of the waste materials.  Consideration should be given to redesigning the building such that water intrusion is eliminated to keep the mold from growing again. Best practices for mold control include:

  • Testing:  Sampling is not necessary if visible mold is present. Visual inspection may be sufficient criteria for developing remediation strategies. Air sampling for molds is often costly and is not always useful to test for mold spores or hyphae because there are no recognized standards for acceptable levels of mold in buildings. Furthermore, because not all molds are toxic in nature, there is no definitive correlation between exposure levels and health effects. However, in some instances, such as when no visible mold is present, sampling may be useful in identifying the species present.  The Occupational Safety & Health Administration (OSHA) states that sampling results can be used as a guide to determine the extent of an infestation and the effectiveness of the cleanup. Sampling and interpretation of results are best left to the industrial hygienist or related environmental health or safety professionals with specific educational expertise. Samples should be analyzed by labs with current certification under the American Industrial Hygiene Association’s Environmental Microbiology Laboratory Accreditation Program (EMLAP). Detailed discussion on this subject is contained in several agency level guidelines by OSHA, EPA, the Center for Disease Control and Prevention (CDC), American Congress of Governmental Industrial Hygienists (ACGIH), and multiple commercial organizations, noted as resources at the end of this paper. 
  • Remediation: Remediation is the process of ridding a building structure of mold growth.  Comprehensive remediation efforts should include examination of hidden areas for mold growth (e.g., between drywalls and inside hidden structures).  This process may require the use of specialized equipment, such as borescopes and moisture meters. The remediation process should include safe disposal of the contaminated waste materials and design changes in order to keep the mold from growing again. Comprehensive, long-lasting remediation efforts are a complex and elaborate process that requires identification, sampling, engineering controls (e.g., ventilation, High Efficiency Particulate Air [HEPA] vacuum), personal protective equipment, respiratory protection, dust suppressions, use of highly hazardous chemicals (biocides and corrosives), as well as disposal of the contaminated waste materials. Therefore, mold remediation should only be conducted by trained professionals with specific field experience in mold removal and disposal. Guidance on the subject of remediation is offered by several agency-level directives from OSHA, EPA, CDC, the National Institute for Occupational Safety and Health (NIOSH), and the American Industrial Hygiene Association (AIHA). Additional resources are identified at the end of this paper.
  • Maintenance: Constant vigilance is required to identify, eliminate or control conditions that may result in high moisture content, such as controlling and managing plumbing leaks, condensation and humidity control. Improved preventive maintenance of existing buildings should include a comprehensive moisture control program that incorporates measures to control water intrusions from outside, grading of the grounds and pumping of the foundations and building infrastructure.

CONCLUDING THOUGHTS: Control of mold begins from the earliest design phase of a building, and requires continued vigilance through inspections, evaluation, and maintenance of building systems.  Buildings should be well-designed, well-constructed, and well-maintained to control temperatures and ventilation to minimize microbial growth. Moisture sources such as incursion points, condensations, spills, leaks and excess moisture in materials should be eliminated, minimized or controlled. Ventilation should be distributed effectively throughout spaces, and stagnant air zones should be avoided. Regular inspections to identify mold markers, such as condensation on surfaces or in structures, visible mold, moldy odor and a history of water damage, leakage or penetration, should be routinely conducted. Persistent dampness and microbial growth on interior surfaces and in building structures should be avoided or minimized, as this may lead to adverse health effects.

For existing structures with mold problems, once the moisture infiltration is mitigated, disposal of the contaminated material and structural repair is important. Vigilant inspection, observation, and proper maintenance processes are the key to healthy buildings. 

Proper notification of, and continued communication with, the stakeholders and the occupants throughout the process will keep interested parties well informed. The information exchange should include the complete disclosure of conditions and the remediation plan, should be timely and transparent, and should address any potential hazards and elicit views on expectations from all stakeholders (e.g., workers, building occupants). 




1World Health Organization (WHO) Guidelines for IAQ-Dampness and Mould, 2009

2Public Health and Economic Impact of Dampness and Mold, David Mudarri* and William J. Fisk+, U.S. Environmental Protection Agency, LBNL-63007


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