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. Mold growth may
also be caused by incomplete drying of flooring materials such as concrete. 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 air-tight, 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. And 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.