MOLD FREQUENCY in BUILDINGS - CONTENTS: at what frequency are various common indoor mold genera/species actually found in buildings?Table of most common building molds. Which molds are most commonly found indoors? Why are some molds reported more often than others?
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Frequency of occurrence of indoor molds by genera/species:
Here is a mold frequency table guide to the most common building molds found in mold test samples collected in buildings, based on surface tape samples submitted to an expert
mycologist in New York State, with additional explanation and interpretation by Daniel Friedman, an expert mold/IAQ/building diagnostic field investigator
also versed in aerobiology and mold lab microscopy and mold identification procedures.
Table of Most Common Indoor Molds Reported by Mold Test Kits
Simple "mold screening methods" which omit the inspection, and "test only" sampling methods, such as air and culture methods
can produce very unreliable results when used quantitatively - as we discuss at IAQ Methods and at other articles at this website. See MOLD GROWTH on SURFACES for an index of what mold genera/species are frequently found on various building surfaces and materials during expert building mold inspections.
Readers should be sure
to see the notes following the table since the data in this table is skewed by variations in the ability of the original sample collectors
to find and recognize important mold contamination in buildings.
Careful visual inspection combined with physical sampling of visible mold or other key building surfaces remain the key
ingredients in a reliable indoor mold investigation.
Easy-to-see molds are over-reported and hard-to-see molds are under-reported in consumer-generated mold tests and samples. This reporting error also confounds attempts to correlate mold related illness and sick building complaints with specific genera or species of indoor mold. Therefore our mold frequency table shown just below reflects what people, including largely amateurs, see and sample in buildings, and it under-reports hard-to-see light colored molds such as many of the Penicillium or Aspergillus species.
Table of Frequency of Occurrence of Indoor Building Molds2
1. J. Haines, New York State Museum, multi-year survey of surface samples collected on adhesive tape and submitted to NY DOS by
home owners or by health department officials. Personal communication to DJ Friedman. Arranged by percent of total samples analyzed.
The contents of this web page are the opinion of the author and are subject to update pending further technical and professional review.
2. Warning: because most of the samples submitted to Dr. Haines were collected by people who were not expert at recognizing
or even finding the most-problematic molds in buildings, there may be an over-reporting of the dark, easy-to-see molds such as the
top three in this list, and an under-reporting of the often light, hard-to-see problematic molds such as Aspergillus. sp.
and Penicillium sp.. In my own field work responding to client-detected mold concerns, in most cases where the occupant
or owner has seen a "scary black mold" or a "toxic black mold" a more careful study of the building discloses that it is the
previously un-detected Aspergillus. sp.
and Penicillium sp. which were the mobile, airborne, and dominant problematic molds to which the occupants were actually
In addition, we have been using special methods to test fiberglass building insulation for Penicillium/Aspergillus sp. in areas where
the insulation has been wet or where insulation has been exposed to active mold growth such as over a wet crawl space or a moldy basement.
I have often found large reservoirs of
these problem molds in building insulation, observing that the reservoir is releasing high levels of airborne mold spores.
This mold contamination is discoverable by contextual inspection and special test methods, but it is not at all visible to the
An exception to the speculation that these small, hard-to-see molds are the more serious problem
in buildings is during amateur cleanup and demolition work without adequate containment measures. Demolition can cause
molds which are not normally airborne, such as Stachybotrys chartarum to become widely dispersed in a building.
3. Some of the molds listed in this table, even though found indoors, are unlikely to be indicative of a growing
mold reservoir of that genera/species. For example, I often find Cladosporium herbarum and certain Basidiomycetes
such as Ganoderma sp./G. applanatum/G. tsuge in indoor air samples but I have not found these genera/species
growing on building materials. Rather they enter in outdoor air.
In conclusion, this interesting table needs additional research with data provided by expert building investigators rather than
self-collected data by individuals who spot first and sample first dark molds on building surfaces. Readers should see
How to Look For Mold.
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Kansas State University, department of plant pathology, extension plant pathology web page on wheat rust fungus: see http://www.oznet.ksu.edu/path-ext/factSheets/Wheat/Wheat%20Leaf%20Rust.asp
"A Brief Guide to Mold, Moisture, and Your Home",
U.S. Environmental Protection Agency US EPA - includes basic advice for building owners, occupants, and mold cleanup operations. See http://www.epa.gov/mold/moldguide.htm
US EPA - Mold Remediation in Schools and Commercial Building [Copy on file at /sickhouse/EPA_Mold_Remediation_in_Schools.pdf ] - US EPA
US EPA - Una Breva Guia a Moho - Hongo [Copy on file as /sickhouse/EPA_Moho_Guia_sp.pdf - en Espanol
"A Brief Guide to Mold, Moisture, and Your Home", U.S. Environmental Protection Agency US EPA - includes basic advice for building owners, occupants, and mold cleanup operations. See http://www.epa.gov/mold/moldguide.htm
"Disease Prevention in Home Vegetable Gardens,"
Department of Plant Microbiology and Pathology,
Department of Horticulture, University of Missouri Extension - extension.missouri.edu/publications/DisplayPub.aspx?P=G6202
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The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume.
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