Causes / Growing conditions for mold

Molds and fungi are found everywhere inside and outside, and can grow on almost any substance when moisture is present. Molds when they reproduce make spores, which can be carried by air currents. When these spores land on a moist surface that is suitable for life, they begin to grow. Molds are essential to the natural breakdown of organic materials in the environment. Mold is normally found indoors at levels that do not affect most healthy individuals. When these levels become abnormally high as determined by indoor air quality testing or a mold inspection, remediation is recommended to be carried out by a professional remediation company.

Because common building materials are capable of sustaining mold growth, and mold spores are ubiquitous, mold growth in an indoor environment is typically related to an indoor water or moisture problem. Incomplete drying of flooring materials such as concrete may also cause mold growth. Leaky roofs, building maintenance problems, or indoor plumbing problems can lead to mold growth inside homes, schools, or office buildings. Another common source of mold growth is flooding.

For significant mold growth to occur there must be a source of water (which could be invisible humidity), a source of food, and a substrate capable of sustaining growth. Common building materials, such as plywood, drywall, furring strips, carpets, and carpet padding are food for molds. In carpet, invisible dust and cellulose are the food sources. After a single incident of water damage occurs in a building, molds grow inside walls and then become dormant until a subsequent incident of high humidity; this illustrates how mold can appear to be a sudden problem, long after a previous flood or water incident that did not produce a mold-related problem. The right conditions re-activate mold. Studies also show that mycotoxin levels are perceptibly higher in buildings that have once had a water incident.

Both our indoor and outdoor environment have mold spores present. There is no such thing as a mold free environment in the Earth’s biosphere. Spores need three things to grow into mold:

  • Nutrients: Food for spores in an indoor environment is organic matter, often cellulose.
  • Moisture: Moisture is required to begin the decaying process caused by the mold.
  • Time: Mold growth begins between 24 hours and 10 days from the provision of the growing conditions. There is no known way to date mold.

Mold colonies can grow inside building structures. The main problem with the presence of mold in buildings is the inhalation of mycotoxins. Molds may produce an identifiable smell. Growth is fostered by moisture. After a flood or major leak, mycotoxin levels are higher in the building even after it has dried out.

Food sources for molds in buildings include cellulose-based materials, such as wood, cardboard, and the paper facing on both sides of drywall, and all other kinds of organic matter, such as soap, dust, and fabrics. Carpet contains dust made of organic matter such as skin cells. If a house has mold, the moisture may be from the basement or crawl space, a leaking roof, or a leak in plumbing pipes behind the walls. Insufficient ventilation can further enable moisture build-up. The more people in a space, the more humidity builds up. This is from normal breathing and perspiring. Visible mold colonies may form where ventilation is poorest, and on perimeter walls, because they are coolest, thus closest to the dew point.

If there are mold problems in a house only during certain times of the year, then it is probably either too airtight, or too drafty. Mold problems occur in airtight homes more frequently in the warmer months (when humidity reaches high levels inside the house, and moisture is trapped), and occur in drafty homes more frequently in the colder months (when warm air escapes from the living area into unconditioned space, and condenses). If a house is artificially humidified during the winter, this can create conditions favorable to mold. Moving air may prevent mold from growing since it has the same desiccating effect as lowering humidity. Keeping indoor air temperature higher than 74 °F (23.3 °C) also has an inhibiting effect on mold growth.

Because common building materials are capable of sustaining mold growth, and mold spores are ubiquitous, mold growth in an indoor environment is typically related to an indoor water or moisture problem. Leaky roofs, building maintenance problems, or indoor plumbing problems can lead to mold growth inside homes, schools, or office buildings. Another common cause of mold growth is flooding.

Removing one of the three requirements for mold reduces or eliminates the new growth of mold. These three requirements are 1) Moisture, 2) Food source for the mold spores (dust, dander, etc), and 3) Warmth (mold generally does not grow in cold environments).

HVAC systems can create all three requirements for significant mold growth. The A/C system creates a difference in temperature that allows/causes condensation to occur. The high rate of dusty air movement through an HVAC system may create ample sources of food sources for the mold. Finally, since the A/C system is not always running – the ability for warm conditions to exist on a regular basis allows for the final component for active mold growth.

Because the HVAC system circulates air contaminated with mold spores and sometimes toxins – it is vital to prevent any three of the environments required for mold growth. A) Highly effective return air filtration systems are available that eliminate up to 99.9% of dust accumulation (as compared to 5% elimination by typical HVAC air filters). These newer filtration systems usually require modification to existing HVAC systems to allow for the larger size of electrostatic 99.9% filters. However, thorough cleaning of the HVAC system is required before usage of high efficiency filtration systems will help. Once mold is established – the mold growth and dust accumulation must be removed. B) Insulation of supply air ducts helps to reduce or eliminate the condensation that ultimately creates the moisture required for mold growth. This insulation should be place externally on the air ducts, because internal insulation provides a dust capture and breeding ground for mold.

Assessment

The first step in an assessment is to determine if mold is present. This is done by visually examining the premises. If mold is growing and visible this helps determine the level of remediation that is necessary. If mold is actively growing and is visibly confirmed the need for sampling for specific species of mold is unnecessary.

Another assessment method is to determine if the premise smells of mold, often described as an earthy or musty odor. However, not all molds produce the telltale mold odors.

These methods are considered to be non-intrusive and only visible and odor-causing molds will be found. Sometimes more intrusive methods are needed to assess the level of mold contamination. This would include moving furniture, lifting and/or removing carpets, checking behind wallpaper, or paneling, checking in ventilation ductwork, opening and exposing wall cavities, etc.

Careful detailed visual inspection and recognition of moldy odors should be used to find problems needing correction. Efforts should focus on areas where there are signs of liquid moisture or water vapor (humidity) or where moisture problems are suspected. The investigation goals should be to locate indoor mold growth to determine how to correct the moisture problem and remove contamination safely and effectively.

The basic goals of any mold investigation are always twofold: 1) find the locations of mold growth, and 2) determine the sources of the moisture. If these can be answered by simpler or more cost-effective methods, mold testing is probably not a wise use of resources.

Many organizations exist that provide certification for mold investigation/assessments. However, only the American Indoor Air Quality Council provides accredited certifications. In the state of Texas there is legislation dictating who can and cannot perform investigation.

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