Using a hand held pump to collect building dust (C) Daniel FriedmanStep by Step Test For Mold Contamination in Fiberglass & Similar Building Insulation Products

  • TEST PROCEDURE for MOLD in FIBERGLASS - CONTENTS: How to test for mold in fiberglass and other fibrous insulation materials - detailed procedure. Where to look for moldy building insulation: conditions, locations, methods. Field Test & Lab Procedures to find mold growth and contamination in building insulation. Testing or inspecting for moldy building insulation or moldy heating or air conditioner duct insulation
  • POST a QUESTION or READ FAQs about how to test for mold contamination in building insulation

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Insulation mold test procedure:

This document describes step by step field test procedures to screen for the presence of mold contamination in fiberglass insulation in residential and light-commercial buildings.

This article series explains 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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Guide to Testing for Mold in Building Insulation

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

This article series 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.

The photo at left, another sample we collected the interior of mold-suspect insulation shows extensive chains of Penicillium/Aspergillus type mold spores, suggesting that this fungus is probably growing in the insulation itself.

Fiberglass in building insulation is a topic I have been testing and studying since 1986, after having traced building mold concerns to a hidden source in this material.

We frequently find high levels of mold-contaminated fiberglass insulation in buildings which contain other large mold reservoirs.

We 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.

Actual Mold Growth in Insulation - 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.

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

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 in this insulation test sample.

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

How to Test Building Insulation for Mold Contamination

We provide the following procedure for testing building insulation for mold for two purposes.

  1. To invite feedback and procedural improvements from other field investigators and building professionals
  2. To provide a simple, inexpensive mold sampling procedure that building owners or occupants of limited financial means can use to get an idea about possible mold contamination in building insulation - a problem area which is often missed by building and mold inspectors.

See INSULATION MOLD CONTAMINATION TEST for more detailed discussion about the occurrence of mold in building insulation.

Visually Inspect Insulation For Mold & Leaks First

Using a hand held pump to collect building dust (C) Daniel Friedman

Before testing apparently "clean" building insulation for mold contamination, look at all of the accessible insulation areas for evidence of visible mold or evidence of leak or water damage that may have wet the insulation.

Adhesive Tape Samples of Settled Dust or Suspected or Visible Mold on Building Surfaces such as Insulation Backing or Kraft Paper, Walls, Wood Framing

Tape sampling (C) Daniel FriedmanMost of this article discusses using methods such as vacuuming or perhaps bulk sampling to sample or test fiberglass insulation for non-visible contamination. But what about sampling visible dust, debris, or mold?

If you see moldy kraft paper backing on building insulation it's reasonable to assume that the insulation is contaminated and that it should be removed, the cavities cleaned, and the cause of mold corrected.

Further mold tests may not be necessary unless needed for medical reasons or for the purpose of comparison with building mold detected in other samples from other areas before or after a building mold cleanup project.

An inexpensive and easy method for collecting settled building dust for screening or for collecting suspected mold or other problem particles from building surfaces requires clear adhesive tape, a clean freezer-type plastic bag, and an examination to choose sampling points that you think are representative of building conditions.

See TAPE & BULK SAMPLING & TESTS for MOLD for details of how to use adhesive tape for surface sampling of dust, particles, or suspected mold growth on building surfaces.

And see FIBERGLASS AIR DUCT MOLD TEST for an example of using adhesive tape to identify mold growth on the interior of HVAC air ducts.

How to Collect Bulk Samples of Insulation to be Tested for Problem Mold Contamination

For people who cannot obtain field services to inspect and vacuum-test building insulation for problem mold, it is possible to cut and remove a square foot of mold-suspect insulation to be sent as a bulk sample to a forensic lab for testing. What we don't like about this approach is that the cost and trouble generally mean that only one or two samples will be collected, reducing our confidence in the conclusion. That is, a lot depends on exactly where and when a mold test sample is collected, and it's a bit too easy to collect a "clean" sample that misses a problem in the building.

If you must collect one or two bulk samples of fiberglass insulation to be tested for mold, we suggest

  1. Collect the sample from the most-suspect area(s) of the insulation, such as areas that are known to have been wet or known to have been exposed to problem locations in a building.
  2. Collect a square foot of insulation, cutting carefully and neatly through the entire insulating blanket, to include the full thickness of the insulation material as well as any plastic, foil, or kraft paper backing on the insulation.
  3. Package the insulation sample in a clean Zip-Lok type plastic bag. It's ok if the insulation is compressed for shipping.

The lab will construct a sterile chamber in which each insulation sample will be agitated and then debris from the insulation will be collected for qualitative analysis.

How to Collect Vacuum Dust Samples of Mold-Suspect Insulation

This procedure prepares dust samples from building insulation for qualitative analysis in a mold lab. (Quantitative analysis by this method would be inaccurate, but it's also unnecessary.)

While some mold inspectors use more sophisticated equipment, the presence or absence of significant problem mold contamination in fiberglass (or other porous) insulation materials, as well as the presence or absence of high levels of other problem particles such as insect allergens, insect fragments (cockroach parts), or even bird dropping contamination can be detected by a competent forensic laboratory from even an amateur-collected insulation sample collected by the process we describe here.

Equipment you'll need to Vacuum-Sample Fiberglass Insulation for Mold

Air sampling cassettes (C) Daniel Friedman

Simple keyboard vacuum used as a building dust collection pump (C) Daniel Friedman

Using a flashlight to see airborne dust (C) Daniel Friedman

Accuracy of Insulation Vacuum Samples for Mold Testing

This mold sample insulation vacuum approach is not suitable for quantitative analysis such as determining the number of mold spores per cubic foot of material.

But then, our tests have demonstrated that there is already an enormous variation in the absolute level of mold spores pulled from building insulation depending many variables:

But this approach will easily tell you what sort of particles and at what density they are found in an insulation sample, and it's easily the most inexpensive method available for testing building insulation.

How to Collect Dust Particle Samples from Building Insulation

Here is a summary of a reasonable tape sampling procedure.

  1. Select the insulation area to be tested
  2. Prepare your vacuum pump, tube, and mounted cassette so that it's ready to use, but leave it turned off.
  3. Using a screwdriver or pencil, make an opening in the center of the test area that penetrates between 1/2 and 7/8 of the thickness of the insulation.
  4. Using the same probing device as in step 2, agitate the insulation from side to side for 3-10 seconds.
  5. Hold the collection cassette facing the insulation and 1/2" to 6" away from the insulation. If you see that your agitation of the insulation has stirred a visible cloud of dust use the longer distance.
  6. Turn on the vacuum pump for 2-10 seconds, then turn it off.
  7. Check the sample: Remove the air sampling cassette and look into the collection slot in a good light. If the collection slot is loaded with insulation fibers and debris the sample is overloaded and you should try again using a shorter vacuum-on interval and a larger distance from the insulation; don't collect the sample more than 12" from the insulation nor without agitating the insulation at all or you risk sampling airborne particles from another source.
  8. Seal the sample collection end and vacuum end with the adhesive tabs provided so that other debris won't enter the device.
  9. Mail your insulation sample along with the control sheet to a mold test lab or forensic lab of your choice.

What the Mold or Forensic Lab Should Report from an Insulation Mold Sample

Dense pen asp mold in insulation

The forensic particle identification (or mold test) lab will need to determine the dominant particles in dust collected from the insulation samples and to compare those results with these base points:

  1. New clean fiberglass insulation
  2. Old fiberglass insulation in buildings and common particles found there
  3. High frequency or dominant-particle presence of problematic mold spores, fungal material, or other contaminants. Our photo at left shows a high level of Aspergillus sp. mold spores and our photo near the top of this page shows mold spore chains confirming actual mold growth in mold-contaminated building insulation.

By examining the density of mold obtained from an insulation sample and also by examining the mold qualitatively (such as for the presence of spore chains of Penicillium sp. or Aspergillus sp., a lab should be able to tell you if the insulation is

  1. Generally clean insulation consistent with new material
  2. Mold contaminated by dust and debris exposure
  3. Contaminated with high levels of insect fragments or other possible respiratory irritants
  4. Mold-contaminated with evidence of mold growth or colonization within the insulation.


Continue reading at VACUUM TEST INSULATION CONTAMINANTS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see BLOWER LEAKS, RUST & MOLD for Readers concerned with mold contamination in heating and air conditioning air handlers and ductwork

Or see FIBERGLASS AIR DUCT MOLD TEST - tape sampling of HVAC duct surfaces


Or see PARTICLE & MOLD LEVELS in DUCTWORK where we describe how to test HVAC systems and ductwork for mold.


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