Mold
By Kenton Shepard
Mold is a controversial subject among home inspectors. The controversy concerns the degree of danger to humans from mold fungus, what those dangers are, under what circumstances sampling is of value and what type of education and training is required for home inspectors to perform sampling capably and with low risk of legal liability. A discussion of these issues lies beyond the scope of this course. Those wishing to know more may benefit form searching the NACHI message boards which contain many threads on the subject. A list of other sources of information is provided at the end of this section.
What is Mold?
Molds are fungi and mold fungi are everywhere, every single home has mold. Fungi form 25% of the earth’s biomass and in general are a natural, necessary part of the global environment.
Mold usually exists in colonies so small that they can’t be seen. It isn’t until mold colonies grow dense enough to be visible that they begin to become a health concern to most people.
Mold fungi reproduce by releasing microscopic spores which are similar to seeds in that spores will produce more fungus. Given the right conditions (the correct temperature, moisture levels and food), fungal colonies can produce enough spores to grow at a phenomenal rate. Enough spores can effect indoor air quality.
Health Risks from Mold
Unfortunately for mold fungi, competition for food exists even between mold species. In an effort to win the food battle, toxigenic mold species have developed toxins (called mycotoxins) to use against their fungal competition. Disagreement exists regarding the overall degree of danger mycotoxins represent to humans.
The U.S. Environmental Protection Agency mold site and the U.S. Centers for Disease Control mold page both agree that high levels of spore concentrations in indoor air are the health hazards most commonly related to mold. Elevated spore concentrations in indoor air can especially affect those with weakened immune systems, lung disease, allergies, asthma or those who have become sensitized.
Those with weakened immune systems may also be at risk from fungal infections, some types of which may be fatal.
Mold Indicates Moisture
Mold fungi typically require moisture levels in materials above 20% to reproduce, so the presence of mold in a home indicates a moisture problem. At moisture levels below about 20% mold fungus activity will stop.
The actual moisture levels at which fungal activity will start and stop varies with the type of fungi and with moisture characteristics of the atmosphere. For this reason a moisture meter can’t be used to accurately determine whether conditions exist which will encourage or prevent fungal growth.
Wood decay fungi cause damage to wood structures by attacking and weakening wood cells. By the time wood decay (rot) becomes visible, wood may have lost up to 50% of its strength. Early (insipient) decay can be extremely difficult to identify, even with a microscope.
“Dry rot” is a misleading term, since decay fungi must have moisture to be active.
Sources for More Information
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