Mold in Fiberglass in Insulation
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Occurrence of mold in fiberglass insulation in buildings: causes, hazards, cure, prevention
Testing or inspecting for moldy building insulation or moldy heating or air conditioner duct insulation
Detailed procedural guide for testing building insulation for mold contamination
When should we test or not test insulation for mold?
Qualitative vs. quantitative tests for insulation mold
Questions & answers about mold-contamination in fiberglass building insulation

Mold contamination occurrences in fiberglass insulation: this article explains the cause, detection, and hazards of mold growth in fiberglass insulation in residential and light-commercial buildings. We illustrate how to find or test for moldy insulation in buildings, the probable cause of mold contamination in building insulation, and how to recognize conditions that make that problem likely in a particular case.

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Mold in Fiberglass Insulation in buildings

This 720x photograph shows active fungal growth along the surface of a fiberglass insulation fiber collected the suspended ceiling of a building suffering wet conditions and moldy in-slab HVAC ducts.

Readers of this document on mold hazards in fiberglass insulation should see How to Test for Mold in Insulation and also read INSULATION MOLD on how to locate and test for moldy insulation in buildings, and for a technical discussion of use of vacuum sampling methods for inspecting building insulation, see Vacuuming exposed insulation.

See Attic Moisture or Mold Sources for a discussion of common sources of moisture in attics that can cause moldy insulation, and similarly, see BASEMENT LEAKS, INSPECT FOR for the same problem in basements. Readers ducting cool air through a crawl space should also see CRAWLSPACE MOLD ADVICE.

This website discusses health hazards associated with moldy fiberglass in buildings, with focus on fiberglass insulation, fiberglass fragments, fiberglass in heating and air conditioning duct work, and invisible but toxic mold growth in fiberglass which has been wet, exposed to high humidity, or exposed to other moldy conditions.

Fiberglass in building insulation is a topic I have been testing and studying for nearly twenty years, after having first traced a building mold contamination reservoir to a hidden source in this material. I frequently find high levels of mold-contaminated fiberglass insulation in buildings which contain other large mold reservoirs. I have also detected high levels of problematic mold in fiberglass building insulation where other mold reservoirs were either not present or had been previously removed.

Our moldy building insulation photo (left, contributed by a reader) shows an obvious case: very wet fiberglass insulation under a roof and extensive black mold growth on at least the insulation surface, probably inside the insulation as well.

But in a more subtle, and not easily visible form, problematic building contamination by mold is often found in otherwise clean-looking basement fiberglass insulation, crawl space fiberglass insulation, fiberglass wall insulation, heating or cooling duct fiberglass insulation, and attic or roof insulation in buildings which have either been wet or have been exposed to high levels of mold from other sources. That "hidden" insulation mold is the focus of our discussion in this article.

Clean-looking Fiberglass Insulation may be Mold Contaminated if Exposed to Wet Conditions

Except for some superficial "dust staining" that is often simply thermal tracking by house dust, the pink fiberglass insulation shown below (left) looked clean. Unlike our black insulation mold photo above, there was no visible mold on the pink fiberglass insulation shown at below left. But vacuuming the center (most clean-looking area) of that mold and lab examination of the vacuum dust sample contents showed the long Penicillium/Aspergillus spore chains (below right) consistent with local problematic mold growth.

Photograph of crawl space insulation which testing found to be mold contaminated.

Photograph of mold spores of Aspergillus sp. found in crawl space fiberglass insulation.

High levels of mold may be present in fiberglass insulation: We have measured very high levels of airborne problematic mold spores which were traced to a building reservoir of moldy fiberglass insulation.

Recapping, the pair of photographs (above) shows fairly clean-looking fiberglass insulation over a crawl space which in fact had been subjected to flooding. While the insulation itself did not appear to have been flooded, and while there was no mold visible on or in this fiberglass insulation, a simple vacuum test demonstrated that the insulation was severely contaminated with Aspergillus sp. mold.

BASEMENT MOLD includes examples of moldy fiberglass insulation found in basements
CRAWLSPACE MOLD includes additional examples of moldy fiberglass insulation found in crawl spaces
CRAWL SPACE DRYOUT PROCEDURES discusses how to dry out crawl spaces to prevent mold growth

Supplementary text continuing below introduces discussion about moldy fiberglass insulation that can be found in more detail at the insulation mold topic links listed just above this sentence.

Fiberglass insulation can host active mold growth

The presence of both mold spore chains and conidiophores of Aspergillus sp. in the insulation test samples whose photos are shown above confirmed that not only was the crawl space ceiling fiberglass insulation moldy, but it was supporting active fungal growth.

Our screening samples confirmed that this mold was present in other building areas, most-likely emanating from this mold reservoir of mold-contaminated fiberglass insulation. In some of cases, non-visible mold contamination in fiberglass insulation has been enough to cause IAQ, health, or other mold-related complaints by building occupants, and in some cases

Photograph: Water stains on drywall suggest this fiberglass insulation may be mold-contaminated.
Mold contamination with Aspergillus sp. was confirmed by special sampling and lab methods.

In the partially-opened basement wall shown here at left, the water track stains on the cavity side of the exposed drywall (shown after a test cut was made) indicate that water passed in this wall from above.

In this circumstance, even when the fiberglass insulation looks clean, I often find high levels of Penicillium sp. or Aspergillus sp. in this material. Comparison tests of fiberglass which is new at a building supply store or in homes where the insulation has not been wet nor infested with rodents or other pests, mold is rarely a problem.

The photo at above right shows a very dense presence of Pen/Asp spores and spore chains as well as a portion of a conidiophore (lower left) in this insulation test sample, indicating that mold appeared to be growing in the insulation, not simply accumulated there from another building mold reservoir.

Where to Look for Mold in Building Insulation

For buildings which do not have other known mold reservoirs, special attention needs to be given to inspecting and testing for problematic mold in

Fiberglass insulation in any building cavity which has been wet.
Fiberglass insulation over wet or damp basements
Fiberglass insulation over crawl spaces
Fiberglass insulation in attics or roof cavities where there has been leakage
Fiberglass insulation in building walls subject to leaks from plumbing failures,previous wetting due to building fire extinguishment, or in freezing climates, walls subject to leaks from ice damming.
Fiberglass heating or cooling duct material, especially if it has been wet from building leaks or A/C condensate mishandling

Moldy building or duct insulation may look clean on visual inspection

Photograph of clean fiberglass insulation fibers - low risk of mold contamination

Photograph of dirty fiberglass insulation fibers - higher risk of mold contamination

What can be tricky in investigations of mold contamination in building insulation is that severely mold-contaminated fiberglass insulation may look pretty clean to the naked eye.

Special vacuum and agitation methods are needed to sample and test this material and special care is needed in choosing the sample or test location when looking for mold in fiberglass or other building insulation.

The left photo above shows clean fiberglass insulation fragments (taken from a sample of new fiberglass building insulation).

The right photo of a sample collected from fiberglass insulation in an older building exposed to moisture and leaks shows a high level of particulate debris, almost certainly including organic debris such as skin cells, animal hair, and insect fragments which can form a base for mold growth.

See Moldy insulation may look clean for details.

When to test building insulation for mold

We do not recommend routine testing of building fiberglass for mold in non-suspect cases. "Spot checks" by "mold testing" in buildings, if conducted without an expert diagnostic visual inspection and history gathering, are simply not reliable and thus not cost-justified.

See When to test insulation for mold for detailed advice about when where how and why to test building insulation for mold contamination.

See When to hire a professional to investigate a building for toxic mold for more detailed advice on deciding when it is appropriate to hire a professional or to perform further mold testing in a building.

See Vacuuming building cavities as a screen for building mold as well as Vacuuming exposed insulation for finding mold-contaminated fiberglass.

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INSULATION MOLD
  Mold in Fiberglass Insulation
  Mold on Books, Book Conservation
  Mold on Fiberboard Insulating Sheathing
  MOLD PREVENTION AFTER FLOODING
  MOLD RESISTANT CONSTRUCTION
  Mold in Foam Insulation
  Moldy insulation may look clean
  Why does mold grow in fiberglass?
  When to test insulation for mold
  How to Test for Mold in Insulation
  References, Fiberglass Hazards
  Vacuuming exposed insulation

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
Environmental Health & Investigation Bibliography - our technical library on indoor air quality inspection, testing, laboratory procedures, forensic microscopy, etc.
Adkins and Adkins Dictionary of Roman Religion discusses Robigus, the Roman god of crop protection and the legendary progenitor of wheat rust fungus.
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 as /sickhouse/EPA_Mold_Remediation_in_Schools.pdf ] - US EPA
US EPA - Una Breva Guia a Moho - Hongo [on file as /sickhouse/EPA_Moho_Guia_sp.pdf - - en Espanol

Fiberglass in buildings: hazards, testing, cleanup, prevention: references & products

For more information about fiberglass as an indoor air quality concern see:

Asbestos: How to find and recognize asbestos in buildings - visual inspection methods, list of common asbestos-containing materials (Asbestos is not fiberglass and vice versa).
BASEMENT MOLD includes examples of moldy fiberglass insulation found in basements
CRAWLSPACE MOLD includes additional examples of moldy fiberglass insulation found in crawl spaces
Duct System Defects
Fiberglass in Indoor Air, HVAC ducts, and Building Insulation, Indoor Air Quality Investigations, building insulation and HVAC duct work insulation hazards
FIBERGLASS HAZARDS
Fiberglass Particle Identification in the Fiberglass Test Laboratory
Fiberglass References - Government Agencies & Authorities list of public documents on fiberglass
Goodman Gray Flex Duct Deterioration and Failures
INSULATION INSPECTION & IMPROVEMENT
Insulation Identification Photographs - Fiberglass insulation photos, yellow, pink, green, white fiberglass identification in building attics, walls, ducts, other locations
Insulation Identification Photographs - Cellulose insulation photos, Mineral wool insulation photos, rock wool insulation photos, cotton insulation photos, balsam wool insulation photos
Insulation Identification Photographs - Vermiculite insulation photos
Lab Identification of Fiberglass photographs and text assist in laboratory identification of fiberglass fibers and fragments in air, dust, or material samples in the laboratory using forensic microscopic techniques.
Mold in Fiberglass building insulation, when, why, and how fiberglass becomes a reservoir of problem mold in buildings.
AIR FILTERS, OPTIMUM INDOOR
Owens Corning Flex Duct Deterioration and Failures
World Trade Center Dust Particle Identification
Fiberglass carcinogenicity: "Glass Wool Fibers Expert Panel Report, Part B - Recommendation for Listing Status for Glass Wool Fibers and Scientific Justification for the Recommendation", The Report on Carcinogens (RoC) expert panel for glass wool fibers exposures met at the Sheraton Chapel Hill Hotel, Chapel Hill, North Carolina on June 9-10, 2009, to peer review the draft background document on glass wool fibers exposures and make a recommendation for listing status in the 12th Edition of the RoC. The National Institute of Environmental Health Sciences is one of the National Institutes of Health within the U.S. Department of Health and Human Services. The National Toxicology Program is headquartered on the NIEHS campus in Research Triangle Park, NC. The National Institute of Environmental Health Sciences is one of the National Institutes of Health within the U.S. Department of Health and Human Services. The National Toxicology Program is headquartered on the NIEHS campus in Research Triangle Park, NC.
Following a discussion of the body of knowledge, the expert panel reviewed the RoC listing criteria and made its recommendation. The expert panel recommended by a vote of 8 yes/0 no that glass wool fibers, with the exception of special fibers of concern (characterized physically below), should not be classified either as known to be a human carcinogen or reasonably anticipated to be a human carcinogen. The expert panel also recommended by a vote of 7 yes/0 no/1 abstention, based on sufficient evidence of carcinogenicity in well-conducted animal inhalation studies, that special-purpose glass fibers with the physical characteristics as follows longer, thinner, less soluble fibers (for 1 example, > 15 μm length with a kdis of < 100 ng/cm2/h) are reasonably anticipated to be a human carcinogen for the listing status in the RoC. The major considerations discussed that led the panel to its recommendation include the observations of tumors in multiple species of animals (rats and hamsters). Both inhalation and intraperitoneal routes of exposure produced tumors, although inhalation was considered more relevant for humans.
Fiberglass insulation mold: occurrence of mold contamination in fiberglass insulation can be impossible to see with the naked eye, but can be significant
World Health Organization International Agency for Research on Cancer - IARC Monographs on the Evaluation of Carcinogenic Risks to Humans - VOL 81 Man-Made Vitreous Fibers, 2002, IARCPress, Lyon France, pi-ii-cover-isbn.qxd 06/12/02 14:15 Page i - World Health Organization, 1/21/1998. - Fiberglass insulation is an example of what IARC refers to as man made vitreous fiber - inorganic fibers made primarily from glass, rock, minerals, slag, and processed inorganic oxides. This article provides enormous detail about fiberglass and other vitreous fibers, and includes fiberglass exposure data.
http://monographs.iarc.fr/ENG/Monographs/vol81/mono81.pdf - the article (large PDF over 6MB)
http://monographs.iarc.fr/ENG/Monographs/vol81/mono81-6A.pdf - article details
http://monographs.iarc.fr/ENG/Monographs/vol81/mono81-6C.pdf - studies of cancer in experimental animals in re vitreous fibers such as fiberglass;
http://monographs.iarc.fr/ENG/Monographs/vol81/mono81-6E.pdf - summary of data reported & evaluation
http://monographs.iarc.fr/ENG/Monographs/vol81/mono81-6F.pdf for the article references
To search the IARC monographs on various environmental concerns and carcinogens, use http://monographs.iarc.fr/ENG/Monographs/PDFs/index.php
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Mold in Fiberglass Insulation in buildings

Clean-looking Fiberglass Insulation may be Mold Contaminated if Exposed to Wet Conditions

Fiberglass insulation can host active mold growth

Where to Look for Mold in Building Insulation

Moldy building or duct insulation may look clean on visual inspection

When to test building insulation for mold

Questions & Answers regarding this article

Ask a Question or Search InspectAPedia

Technical Reviewers & References

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

Fiberglass in buildings: hazards, testing, cleanup, prevention: references & products