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Mold contamination occurrences in fiberglass insulation:
This article, the head of a series of texts about mould contamination in building insulation, 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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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 or A Secondary Airborne Mold Source
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.
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.
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.
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
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.
For buildings which do not have other known mold reservoirs, special attention needs to be given to inspecting and testing for problematic mold in
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.
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 Attic Moisture or Mold Sources for a discussion of common sources of moisture in attics that can cause moldy insulation, and similarly,
Readers ducting cool air through a crawl space should also see CRAWLSPACE MOLD ADVICE.
Continue reading at TEST CHOICES for MOLD in FIBERGLASS or select a topic from the More Reading links shown below.
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Technical Reviewers & References
Fiberglass in buildings: hazards, testing, cleanup, prevention: references & products
For more information about fiberglass as an indoor air quality concern see: