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This document provides information about the cause, detection, and hazards of mold growth in fiberglass insulation in residential and light-commercial 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 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 Moisture or Mold 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.

Mold is often found in 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.

Here we discuss 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.

© Copyright 2009 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

Mold in Fiberglass Insulation in Buildings

Fiberglass in building insulation is a topic I've been testing and studying for several years, after having traced building mold concerns 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.

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.

This pair of photographs shows fairly clean-looking fiberglass insulation over a crawl space which in fact had been subjected to flooding. 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

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

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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FIBERGLASS HAZARDS
  Recognizing Fiberglass Duct Insulation  Recognizing Fiberglass Duct Insulation
  Lab Identification of Fiberglass
  Fiberglass Fragment Hazards
  Fiberglass Detection in Building Air
  Mold in Fiberglass Insulation
  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
  Fiberglass Hazard References

INSULATION INSPECTION & IMPROVEMENT

Vacuuming exposed insulation

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

• Fiberglass building insulation and HVAC duct work insulation hazards
• 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.
• Fiberglass insulation mold: occurrence of mold contamination in fiberglass insulation can be impossible to see with the naked eye, but can be significant

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More Information on Building Diagnostic Inspections and Repairs

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

• Fiberglass in Indoor Air, HVAC Ducts, and Building Insulation
• Fiberglass Particle Identification in the Fiberglass Test Laboratory
• Goodman Gray Flex Duct Deterioration and Failures
• Mold in Fiberglass Insulation
• Optimum Indoor Air Filters
• Owens Corning Flex Duct Deterioration and Failures
• World Trade Center Dust Particle Identification

For more information about asbestos as an indoor air quality concern with focus on easy ways to identify asbestos materials in buildings, see:

• Asbestos Identification in Buildings: How to find & identify asbestos-containing materials
• Asbestos in Good Condition
• Asbestos HVAC Ducts - Asbestos Materials On or In Heating and Cooling Duct Work
• Asbestos paper duct wrap
• Asbestos Transite Chimneys, Flues, & Pipes in Buildings
• Asbestos under the microscope
• Asbestos Vibration Dampers & Asbestos in the Air Handler
• Ceiling tiles: How to recognize ceiling tiles that may contain asbestos
• Examples of unusual uses of asbestos in buildings

• Fiberglass in Indoor Air, HVAC ducts, and Building Insulation, Indoor Air Quality Investigations: (this article)
• Mold in Fiberglass, when, why, and how fiberglass becomes a reservoir of problem mold in buildings.
• 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.
• Asbestos: How to find and recognize asbestos in buildings - visual inspection methods, list of common asbestos-containing materials

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