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This document provides information about the cause, detection, and hazards of mold growth in foam insulating materials in comparison with fiberglass insulation in residential and light-commercial buildings. This website discusses health hazards associated with mold in buildings. Because no amount of insulation can keep a drafty building warm, also review Priorities for building energy efficiency. Also see HEAT LOSS INDICATORS (where is the building losing heat during the heating season, or gaining un-wanted heat during the cooling season), and see HEAT LOSS R U & K VALUE CALCULATION for a guide to calculating heat loss (or gain) rates for buildings and building insulation.

Readers should also see Icynene Foam Spray Insulation which assists in visual identification of foam spray insulation products, and Foam Insulation Types - Visual Id which provides simple definitive tests anyone can perform to distinguish among UFFI, Icynene, and Latex foam insulation products.

Also see Mold in Fiberglass Insulation © 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.

What are the Comparable Risks of Mold Growth in Foam Insulation vs. in Fiberglass Building Insulation?

The following opinions about mold risk associated with different types of insulating products in buildings are based on 30 years of field investigation experience and 20 years of forensic laboratory experience and the results appear intuitive, unambiguous, and compelling. However I add that controlled authoritative research on this question has not been completed and additional factors may be involved. The author has no financial nor any other relationship with products or services discussed at this website.

Lower Mold Risk Seen with Solid Insulation Products than with Open Products such as Fiberglass

In general, we find fiberglass a ready mold harbor and we do not find mold in foam insulation products such as spray-on Icynene foam insulation or in foam insulating boards. Closed cell foam insulation does not pick up moisture nor organic dust so it is less friendly to mold growth within itself.

Closed cell foams keep out moisture and may be chemically resistant to mold

If we expose any closed cell foam to the same conditions, because moisture and particles do not enter its interior, it is resistant to becoming a mold reservoir itself. It is possible that the chemistry of some foam insulations is also mold-resistant, just as I’ve observed that blown-in cellulose insulation is mold resistant, probably because of the chemistry of the fire retardant with which it is treated.

Open celled insulation products and fiberglass appear more friendly to mold growth

If we expose fiberglass to water, leaks, or high moisture there is a risk of mold growth within the insulation itself as well as on surfaces of the cavity where it resides. The level of risk of mold in fiberglass depends on many factors such as the age of the insulation, the amount of organic dust and debris in its environment, the level of moisture to which it is exposed, and other variables.

Other sources of mold resistance with foam insulating products

We speculate that there may be a further mold resistance when using a spray-in foam insulation product insofar as the foam forms a tight bond between the foam and the sprayed-on surface such as the sides of rafters or wall studs or floor joists and the underside of roof, wall, or floor sheathing. This tightness may resist moisture passage into the building cavity and thus substantially reduce the chances of mold growth on wood or other organic surfaces in those areas.

Finally, the installation of an insulation product which is less leaky around wall penetrations, such as receptacles, switches, light fixtures, windows, doors, will move less air through the building cavities and thus would be expected to move less moisture through those spaces, also reducing the probability of a mold problem therein.

What Mold, Rot,or Damage Concerns Occur When Using Foam Insulation In Buildings?

Closed building cavities may be at risk of rot or mold from external leaks

There is one fly in the ointment of this insulation mold balm, however. In some locations, perhaps such as a cathedral ceiling, a leak from the building exterior that penetrates the cavity will send water in to a location where it is both hard to detect and slow to dry out. The result can be severe rot and structural damage where undetected leaks into the building envelope occur. We ’ve seen this in particular in some of the “hot roof” designs on newer homes.

Mold risk is higher on EIFS or Synthetic Stucco Covered Buildings

We’ve seen this trapped-moisture problem along with mold problems in extreme where a different foam insulation approach was used: the construction of synthetic stucco building exteriors (EIFS). In this last example, leaks at wall penetrations of synthetic-stucco-covered buildings (using the EIFS system) send water behind foam panels on the building exterior. Water in the building cavities is very slow to dry out, hard to detect, and can lead to major building damage and mold cleanup costs. The EIFS system requires virtually perfect workmanship and installation detailing – a requirement that is unrealistic in most construction environments.  

EIFS/synthetic stucco covered buildings is certainly different from an Icynene foam insulated building because the former is installed on a building exterior, forming a water-tight (but leaky) skin over conventional wall cavities which may be insulated with fiberglass, while the latter, Icynene foam, is used to fill those same wall cavities.

Mold growth found on surface of solid foam insulating boards

On occasion we've found black mold, usually a member of the Cladosporium sp. family growing on the surface of Styrofoam ™ insulating boards. Without more research we don't know if this growth was due to organic dust and debris on the insulating foam board surface, or if there were other causal factors.

Summary of Mold and Rot Risks for Fiberglass vs. Solid Foam Insulating Products

In sum, I would project lower risk of in-building-cavity building mold problems in buildings where Icynene foam installation is installed than in buildings of the same design where fiberglass insulation is used in the same cavities, but I’d warn that exterior leaks into the building create different but potentially significant damage and mold or rot risks in all cases.

We welcome comment, criticism, feedback from readers or from product manufacturers on this matter. As an independent building failures researcher/writer, the author has no economic nor other relation with these products, and remains vitally interested in accurate, informed data.

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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
    Mold Resistance of 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

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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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