Photograph of Moldy visible growing on a fiberglass insulation fiber  © Daniel FriedmanTest Choices to Screen for Mold in Fiberglass in Insulation

  • TEST CHOICES for MOLD in FIBERGLASS - CONTENTS: Choices of fiberglass mold test alternatives for field and laboratory investigation of building mold contamination. 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.
  • POST a QUESTION or READ FAQs about methods for testing for the presence of mold contaminants in fiberglass or other building insulation products

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Fiberglass insulation mold contamination test details:

This document discusses choices of test methods to screen for toxic or allergenic mold contamination in fiberglass building insulation in residential and light-commercial buildings.

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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How to Test Building Insulation for Mold Contamination

Fiberglass testing (C) Daniel FriedmanThis article 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.

Our page top photo shows a Burkard personal air sampler that with clever manipulation can be used to test fiberglass building insulation for contaminating particles including mold, insect fragments, pollen, or other debris.

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.

Watch out: Our photo of clean-looking insulation in a basement ceiling (at below left left) does not provide evidence that insulation testing was necessary for that building.

But a case history of occupant complaints, a wet basement, and previous storage of moldy materials in the basement that had been removed at the time of our inspection led us to test and confirm that this insulation was severely contaminated with Penicillium sp. mold.

Reader Question: How should we sample fiberglass insulation for mold when investigating a building?

Photograph moldy fiberglass insulation in a basement - it looked clean but it was not - © Daniel FriedmanI believe that there is mold that is not visible to the eye, but how do you confirm that it is there? Send a piece of the insulation to a lab for analysis? I’m a mold inspector in Minneapolis, Minnesota and we have a lot of damp insulation in basements here.

Sometimes I see spots on the insulation and know that there is obvious mold, but I have long suspected (based on smell and moisture readings) that some mold might not be visible to the eye. Is it just that it is in early growth stage so the colonies are too small to see?

And again, how do you verify that this is the case – by samples submitted to the lab? I was on the site searching for information on mold in insulated ducts. - Vickie Swenson, CRMI Minnesota Mold Inspection (612) 508-2742


Answer: Detailed Description of Methods for Testing Building Insulation for Mold

Fiberglass testing (C) Daniel FriedmanYou are quite right that it can be impossible to see mold in some materials including fiberglass insulation. Sometimes fiberglass looks very very clean to the naked eye, but is chock full of Aspergillus or Penicillium.

There are several similar ways to test insulation that does not already give visual evidence of a mold problem.

Air Sampling Cassettes for Insulation Mold Test

We use an air sampling cassette such as an Air-o-Cel or Allergenco unit with a vacuum pump set to move air at the proper flow rate for the cassette (typically 10 lpm). The sampler is held 1-4 inches away from the insulation and then with the pump running we poke or agitate the suspect insulation to stir a particle release.

The sample interval needs to be short - often just 5-20 seconds in duration since otherwise you risk overloading the cassette with fiberglass particles.

At ACCURACY OF VARIOUS MOLD TEST METHODS we include photos of particle traces on microscope slides that can help you recognize when a dust sample is overloaded and thus hard to analyze in the lab.

Our photo (above left) shows a more complicated version of this test about to start. In this case we were using two air sampling pumps and two different brands of sampling cassettes in order to compare their behavior during dust sampling. In the foreground you can just make out a special timer-switch that we used to turn on and off both pumps simultaneously.

If you are in doubt or inexperienced, try making three sample cassettes of 5, 10, and 20 second durations, agitating the insulation about the same degree in each case and keeping about the same distance.

The time and distance are not critical as long as we make clear that this is a qualitative test for the presence or absence of high levels of mold or other particles in the insulation, not a quantitative test.

Burkard Personal Air Sampler and Prepared Slide for Insulation Mold Test

A second method for testing fiberglass insulation that we have used with good results was to run a Burkard personal air sampler with a prepared collection slide mounted in the device for a 15-second interval, holding the sampler one to six inches away from the insulation during agitation of the insulation itself.

You can simply use a pencil to poke the insulation during sampling. As with the air sampling cassette approach above, make several test samples at different sampling durations to be sure you have a good sample that is not overloaded.

Alternative, low-cost Air Pumps for Building Insulation Mold Testing

Simple keyboard vacuum used as a building dust collection pump (C) Daniel FriedmanWhile we prefer using a calibrated instrument for pulling particles from building insulation to screen for mold contamination, considering that a reasonable mold contamination test is qualitative and that precise mold counts are inappropriate (and would be misleading), as long as your air pump or vacuum device produces a flow-rate within the operating range of your sampling cassette or slide, you can use less costly devices such as the keyboard vacuum pump shown here.

Watch out: the airflow rate of portable battery operated pumps such as shown here varies widely from device to device as well as depending on battery condition.

For field use in testing insulation, we tested ten low-cost portable pumps in our forensic laboratory, selecting a subset that consistently delivered 10-15 LPM with fresh batteries .

Constructing a Clean Test Chamber to Screen Insulation for Mold

In the laboratory, if we receive a bulk sample of suspect insulation, in addition to inspecting the insulation itself in the stereo microscope and high power transmitted light forensic microscope, we sometimes use a third sampling method that is most suitable for a variety of suspect, perhaps dirty and loose materials.

We construct a test chamber using a cardboard box lined with a new clean plastic garbage bag.

The bag lines the box, the sample is placed into the box, the box is sealed. We cut an opening sufficient to admit or affix our air sampling cassette, then we agitate the box for 30 seconds before pulling a vacuum sample from the box itself.

This method also can reduce overloading the sample with fiberglass particles.

Quantitative Analysis of Insulation Samples for Mold Contamination

It is possible to perform quantitative analysis of insulation or other fibrous materials or dust samples for mold contamination using a wash and filter method that collects most particles from the insulation sample into a liquid for further processing and particle counting.

We do not agree that the apparent accuracy of this method is real, and we suspect that except for controlled technical studies it is not appropriate.

  1. Fungal contamination within a fiberglass sample varies widely even within the same building area depending on proximity to a leak
  2. Fungal contamination within fiberglass insulation in a building varies by distance to an external airborne mold source such as moldy contents stored in a basement below a fiberglass-insulated ceiling
  3. Fungal contamination in fiberglass insulation in a building will vary by other factors such as insulation age, density, installation details, presence or absence of vapor barriers, air movement patterns, etc.

Therefore a quantitative analysis of mold spores per cubic inch, meter or other volume of fiberglass insulation may be very precise (lots of decimal places) but inaccurate as an estimator of size of the problem mold reservoir.

Should All Building Insulation be Tested for Mold?


We do not recommend testing all insulation for mold. The decision to test insulation for mold needs to be made based on a careful building inspection and case history, including visual evidence of leaks or the presence of exposed fiberglass over an area known to be or have been subject to a large mold contamination problem or a mold remediation project.


Continue reading at TEST PROCEDURE for MOLD in FIBERGLASS about just how fiberglass mold tests are conducted in the field or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

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