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Photograph of light yellow mold found on oriented strand wood sheathing in a wet basement. The Most Common Indoor Molds Found in Buildings

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.

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- Daniel Friedman, Publisher/Editor/Author - See WHO ARE WE?

Table of Most Common Indoor Molds Reported by Mold Test Kits

Photo of mold on roof sheathing undersider in an attic - white mold (C) Daniel FriedmanSimple "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
MoldPercent of
Samples		MoldPercent of
Samples
Cladosporium sp.16.67Ceratocystis sp.0.49
Cladosporium sphaerospermum.16.57Aureobasidium pullulans0.49
Stachybotrys chartarum16.37Peziza cerea0.49
Aspergillus sp.06.02Aspergillus versicolor0.39
Penicillium sp.03.85Unid. wood rot fungus0.39
Unidentified mold03.85Mucor sp.0.39
Ulocladium sp.03.06 Cladosporium herbarum0.39
Cladosporium cladosporioides02.47Chaetomium murorum0.30
Non-sporulating fungi02.47 Acrodictys sp.0.30
Chaetomium globosum02.37 Aspergillus niger0.30
Alternaria sp.02.17Papalomyces0.30
Chaetomium sp.01.97Cunninghamella blakesleana0.20
Ulocladium sp.01.97Paecilomyces varioti0.20
Alternaria alternata01.97Oidiodendron sp.0.20
Penicillium/Aspergillus sp.01.28Memnoniella echinata0.20
Acremonium sp.0.99Microascus triganosporus0.20
Chrysosporium sp.0.89Dendriphiella sp.0.20
Dicyma olivacea0.79Cladosporium oxysporium0.20
Gliomastix murorum0.69Ulocladium botrytis0.20
Meruliporia incrassata0.69Verticllium sp.0.20
Gliomastix sp.0.59 Trichoderma harzianum0.20
Phoma sp.0.49Chaetomium piluliferum0.20
Ascotricha chartarum 0.20 Bispora betulina 0.20
MILDEW in buildings ? 0.00  

Notes to Table

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 exposed.

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 naked eye.

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.

4. For identification photographs of mold in buildings see MOLD ATLAS & PARTICLES INDEX; for photographs of mold under the microscope see MOLD by MICROSCOPE.

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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