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Idaho Home and Building Inspector

All About Mold

Introduction to Molds

Courtesy of

Microbial growth Microbial growth on sheetrock
wall in basement.

Molds create tiny spores to reproduce. Mold spores waft through the indoor and outdoor air continually. When mold spores land on a damp spot indoors, they may begin growing and digesting whatever they are growing on in order to survive.

There are molds that can grow on wood, paper, carpet and foods. When excessive moisture or water accumulates indoors, mold growth will often occur, particularly if the moisture problem remains undiscovered or un-addressed. There is no practical way to eliminate all mold and mold spores in the indoor environment. The way to control indoor mold growth is to control moisture.

Basic Mold Cleanup

The key to mold control is moisture control. It is important to dry water damaged areas and items within 24-48 hours to prevent mold growth. If mold is a problem in your home, clean up the mold and get rid of the excess water or moisture. Fix leaky plumbing or other sources of water. Wash mold off hard surfaces with detergent and water, and dry completely. Absorbent materials (such as ceiling tiles and carpet) that become moldy may have to be replaced.

Ten Things You Should Know About Mold

  1. Potential health effects and symptoms associated with mold exposures include allergic reactions, asthma, and other respiratory complaints.
  2. There is no practical way to eliminate all mold and mold spores in the indoor environment; the way to control indoor mold growth is to control moisture.
  3. If mold is a problem in your home or school, you must clean up the mold and eliminate sources of moisture.
  4. Fix the source of the water problem or leak to prevent mold growth.
  5. To decrease mold growth, indoor humidity should be reduced to a range between 30%-60% by: venting bathrooms, dryers, and other moisture-generating sources to the outside; using air conditioners and de-humidifiers, increasing ventilation and using exhaust fans whenever cooking, dishwashing, and cleaning.
  6. Clean and dry any damp or wet building materials and furnishings within 24-48 hours to prevent mold growth.
  7. Clean mold off hard surfaces with water and detergent, and dry completely. Absorbent materials such as ceiling tiles, that are moldy, may need to be replaced.
  8. Prevent condensation: Reduce the potential for condensation on cold surfaces (i.e., windows, piping, exterior walls, roof, or floors) by adding insulation.
  9. In areas where there is a perpetual moisture problem, do not install carpeting (i.e., by drinking fountains, classroom sinks, or on concrete floors with leaks or frequent condensation).
  10. Molds can be found almost anywhere. They can grow on virtually any substance, providing moisture is present. There are molds that can grow on wood, paper, carpet, and foods.
Standing water in crawlspace Standing water in the crawlspace. A major contributing factor to mold growth.
Microbial growth Microbial growth on underside of roof sheathing.
Snow buildup Snow buildup against side of house has led to water seepage into garage.
Microbial growth Microbial growth on sheetrock wall in garage due to snow pack against building.
Microbial growth Microbial growth on sheetrock walls in kitchen due to leaky sink.
StandiMicrobial growth Microbial growth on structural components of crawlspace due to leaky toilet.


There are more than 160 different species of Aspergillus, 16 of which have been documented as etiological agents of human disease. Aspergilli are probably the most common group of fungi in our environment. Many species of the genus are frequently isolated from a variety of substrata, including forage products, grains, nuts, cotton, organic debris, and water damaged organic building materials.

Due to the ubiquity of the aspergilli within the environment, man is constantly exposed to these fungi. The diseases caused by species of Aspergillus are relatively uncommon and are rarely found in individuals with normally functioning immune systems. However, due to the substantial increase in populations of individuals with active immune suppression, such as individuals with HIV, chemotherapy patients, and those on corticosteroid treatment, contamination of building substrates with fungi, particularly Aspergillus species have become an increasing concern. Aspergillosis is now the second most common fungal infection requiring hospitalization in the United States.

Aspergillus fumigatus

The most frequently encountered opportunistic Aspergillus pathogen, Aspergillus fumigatus, is seen most abundantly in decomposing organic materials. It grows well at temperatures up to 55 degrees C, self-heating compost piles provide an excellent environment for the fungi. Compost made up of chipped branches and leaves will often yield a massive and virtually pure culture of A. fumigatus. A. fumigatus has been reported to be the major organism isolated from air samples obtained near compost sites. People who handle compost or decomposing haystacks often develop hypersensitivity to spores of Aspergillus and after exposure may suffer a severe allergic response.

Aspergillus flavus

Aspergillus flavus is the second most frequently encountered fungi in cases of infection with Aspergillus species. In addition to causing infections, Aspergillus flavus is also known for its production of aflatoxin, one of the most potent carcinogens known to man. Concern about aflatoxin began in the 1960s after some 100,000 turkey poults in Great Britain died as a result of ingesting feed tainted with aflatoxin. When it became evident that aflatoxin was highly carcinogenic, most industrialized countries established tolerances for aflatoxin levels in food and feeds. The risks associated with airborne exposure to aflatoxin in contaminated buildings, as with other mycotoxins, has not been adequately studied.

Aspergillus niger

Aspergillus niger is the third most common aspergilli associated with disease, it is more common than any other Aspergillus species within the genus, and it is found in and upon the greatest variety of substrates. It is commonly associated with "fungus ball", a condition wherein fungus actively grows in the human lung, forming a ball, without invading lung tissue.

Aspergillus in Hospitals

Invasive aspergillosis occurs most frequently among highly immunosuppressed patients, the presence of Aspergillus spores in hospital air has important implications. Aspergillus spores frequently occur in hospitals throughout the world and a number of severe outbreaks resulting in deaths due to disseminated invasive aspergillosis have been reported following renovation activities in hospitals. A study of 39 bone marrow transplant patients who resided in rooms equipped with whole wall laminar flow HEPA filtration units reported no cases of nosocomial aspergillosis. In sharp contrast, 14 cases of nosocomial aspergillosis in 74 bone marrow transplant recipients occurred in patients housed elsewhere. It is critical that adequate engineering controls are implemented during renovations at hospitals or at any facility the immunosuppressed frequent.


Penicillium sp. - (Aw 0.78)3

A wide number of organisms belong to this genus. Identification to species is difficult. Often found in aerosol samples. Commonly found in soil, food, cellulose, paint, grains, compost piles, carpet, wallpaper, and in interior fiberglass duct insulation.

Although this fungus is less allergy-provoking than the other molds, Penicillium is reported to be allergenic (skin), and it may cause hypersensitivity pneumonitis and allergic alveolitis in susceptible individuals. It can cause other infections such as keratitis, penicilliosis, and otomycosis. Some species can produce mycotoxins including 1). Ochratoxin that is damaging to the kidneys and liver and is also a suspected carcinogen; there is also evidence that it impairs the immune system. 2). Citrinin that can cause renal damage, vasodilatation, and bronchial constriction. 3). Gliotoxin which is an immunosuppressive toxin and 3). Patulin that is believed to cause hemorrhaging in the brain and lungs and is usually associated with apple and grape spoilage. It can also cause extrinsic asthma. P. camemberti has been responsible for inducing occupational allergies among those who work with soft white cheeses on which the fungus grows. P. chrysogenum has been found on building materials, including paints, chip boards, and wallpaper. Cultivation - Potato dextrose agar or Malt extract agar, 24 degrees C.

Penicillium brevicompactum

Commonly found in water-damaged carpet, wallpaper, and some types of insulation. Penicillium is reported to be allergenic (skin), and it may cause hypersensitivity pneumonitis and allergic alveolitis in susceptible individuals. It can cause other infections such as keratitis, penicilliosis, and otomycosis. Penicillium brevicompactum can produce the mycotoxin mycophenolic acid.

Penicillium chrysogenum

This species, formerly known as Penicillium notatum, was one of the first known producers of penicillin. It is commonly found and can act as a food source for some types of dust mites. Penicillium chrysogenum is often found growing as a dark green colony and can produce the mycotoxins roquefortine C, chrysogine, and meleagrin.


Considerable recent media attention has been focused on the fungi Stachybotrys chartarum (atra), particularly after a number of infant deaths in Cleveland from pulmonary hemosiderosis associated with extensive contamination of residences with this fungi. Research indicates that contamination of structures with Stachybotrys fungi is much more common than originally believed.

Stachybotrys thrives on water damaged cellulose rich materials in buildings such as sheetrock paper, ceiling tiles, cellulose containing insulation backing, and wallpaper. An extended saturation time and/or consistently high levels of humidity are required for this fungi to proliferate. Thus, in a majority of cases where Stachybotrys is found in buildings, the water damage that occurred often goes unnoticed or ignored by maintenance personnel that are unaware of the implications of such contamination.

In sharp contrast, single or sudden water damage events that occur where drying of water damaged material takes place more quickly tend to support the growth of more xerophilic fungi such as Penicillium and Aspergillus species.

Symptoms of Exposure

The presence of Stachybotrys fungi in buildings is significant because of the mold's ability to produce mycotoxins, metabolites of fungi that can cause adverse health effects in humans and animals. Although most molds produce mycotoxins, those produced by Stachybotrys are extremely toxic, are suspected carcinogens, and are immunosuppressive. Exposure to these toxins can occur through inhalation, ingestion, or dermal exposure. Symptoms of exposure to Stachybotrys toxins include dermatitis, cough, rhinitis, nosebleeds, cold and flu symptoms, headache, general malaise, and fever. Much of what is known about stachybotrystoxicosis has been gleaned from observation of exposed livestock.

Animals exposed to high levels through ingestion of contaminated forage die rapidly due to massive hemorrhaging, both internal and external. Exposure to lower levels over time leads to severe immune system suppression since afflicted animals often suffer from septicemia and succumb to a number of opportunistic infections.

Testing for Stachybotrys

As a general rule, air sampling for Stachybotrys yields unpredictable results because of a number of factors. When significant Stachybotrys contamination is present, other fungal contaminants are usually present as well. When conducting sampling using the Andersen N-6, generally other fungal contaminants will tend to overwhelm the Stachybotrys spores in culture, due to their more rapid growth rate, even when using selective media such as cellulose agar.

In addition, most commonly encountered fungal spores such as those of Aspergillus and Penicillium tend to be much more easily aerosolized than Stachybotrys, thus further amplifying the recovery of the less significant contaminants. Typically under active growth conditions, the spores of Stachybotrys adhere to one another in a sticky sack, making passive aerosolization even more difficult. However, once a Stachybotrys contaminated surface has dried for an extended period of time the sticky sack desiccates and the spores are released much more readily.

Due to these factors, a visual inspection of the subject building is the best method of identifying a potential Stachybotrys contamination problem and requires a trained eye. Recognizing that Stachybotrys requires constant moisture and cellulose for growth helps the inspector narrow down potential sources. Stachybotrys typically appears as a sooty black fungus occasionally accompanied by a thick mass of white mycelia. Bulk or surface sampling of suspect materials should be conducted using caution and removed to the laboratory for identification by light microscopy. New inexpensive techniques are also currently available to measure specific mycotoxins produced by Stachybotrys and can assist the inspector in determining the toxicity of the strain isolated. Site-specific analyses should be discussed with the inspector's laboratory.

Sample QEESI Report

The Quick Environmental Exposure and Sensitivity Inventory (QEESI) was developed as a screening questionnaire for multiple chemical intolerances (MCI).

pdf Sample QEESI Report

Building Specs' Clients Are Saying:

"Thanks so much for the report. Covered the major items with the builder today and they agreed to fix or remediate them. The water in the crawl space and the dryer vent line are huge finds. Thank you for your thoroughness!"
Ryan Munson, Home Buyer