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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.

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.

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Where and why does mold grow in fiberglass?

The left photo shows how fragile is the fiberglass insulation in some HVAC ducts. The rough surface attracts and collects organic and other particulate debris moving through the duct system (unless good filtration is installed at the return air inlets).

The surface of an HVAC duct lined with fiberglass cannot be mechanically cleaned - you can see what happens when someone tries to brush or vacuum it by looking at this photo. Once disturbed by improper "cleaning' efforts, the release of airborne asbestos in the building will certainly increase. If this insulation is wet by leaks or improper condensate handling, or if the building is exposed to high levels of airborne mold from another source, ducts that look like this are likely to become a problem mold reservoir and will need to be replaced.

The second photo at above right shows typical debris, usually skin cells and fabric fibers, which collects on the rough surface of exposed fiberglass inside ductwork. A return opening filter would have helped keep this duct clean and thus extend its life.

Water or condensate leaks into an HVAC duct system such as those shown by the above photographs of stains on the interior of this rooftop mounted commercial HVAC duct (left) and indoor residential air handler unit (right), are an invitation to mold or bacterial contamination in the system.

DF-OPINION: it is more (or less) likely that problematic mold will be found growing in or present in building insulation at a level sufficient to be a potential problem for building occupants in these conditions:

• Low-risk insulation: Mold requires moisture and organic material for nourishment, as well as other growing requirements that vary by mold genera and species. So perfectly clean, dry fiberglass or other building insulation is unlikely to harbor a problem mold reservoir.
  
  
• Wet or "dirty" building insulation: often is found to be moldy, either on the kraft paper or foil/paper insulation backing or in the insulation itself. Insulation which is old and has become populated or "soiled" with organic debris such as animal dander (a home housing animals, especially dogs) or insect fragments (an old house with old insulation) contains plenty of organic debris which can support fungal growth. When such insulation is wet by a single event such as a roof leak or basement flood or when it is exposed to recurrent high interior moisture conditions, the growth of problem mold is a real risk. If there are building occupant IAQ complaints, investigation of the insulation may be in order in this case.
  
  
• Clean fiberglass insulation exposed to moldy air: I have found very high levels of mold contamination in otherwise apparently clean fiberglass insulation in cases where the insulation has been exposed to high levels of moldy air.
  
  Aspergillus sp. and on less frequent occasions, Penicillium sp. or even basidiomycetes are found in insulation which may be rather new and which may appear perfectly clean to the naked eye. A typical scenario producing this condition is the presence of un-protected, exposed fiberglass insulation in the ceiling of a basement where there has been a significant mold contamination, perhaps even a mold remediation project. High airborne mold levels readily move small spores such as those in the Aspergillus/Penicillium group through building insulation by ordinary indoor air and convection currents.

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FIBERGLASS HAZARDS
  Recognizing Fiberglass 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

• 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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• Environmental Health & Investigation Bibliography - our own technical library on indoor air quality inspection, testing, laboratory procedures, forensic microscopy, etc.
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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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