Dark side of insulation

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Magnified mildew growing in indoor environment. Source: Bob Blaylock

Building insulation has become a modish activity in the western world since the 1980s. Considerable benefits can accrue in energy conservation, occupant comfort and reduction of noise pollution from external sources. A dark side of insulation arises, however, from its trapping of radon gas, cigarette smoke, household sprays and other toxins within the enhanced imperviousness of the building skin. Furthermore, insulation can promote the entrapment of moisture, that in turn may increase the formation of molds and mildews, some of which contain toxic species.

Compounding the problem of trapping indoor air pollutants, some insulation techniques employ fibers and chemicals that themselves have adverse human health effects including toxicity risks. While use of asbestos has been a long known risk, there are a host of recently developed chemical substances and fibers that pose entirely new risks to building occupants.

Improved approaches to building insulation may derive from greater control over building insulation subsidies by local and state agencies, rather than arbitrary centralized national rules, that may not have adequate understanding of local microclimates and radon risks in sub-soils.

Government inducement to insulate

Magnified view of rockwool insulation fibers. Source: Achim Hering

Governments, particularly in western countries, have rushed into the subsidization and mandating of building insulation, initially under the mantle of improving national energy security and reducing energy costs for homeowners and businesses. These well-meaning programs have produced many of the intended benefits including reduction of outdoor air pollution and reduction of greenhouse gases from energy conservation.

Government programs particularly prevalent in Western Europe and the USA, have often promoted building insulation agressively through the following inducements and mandates:

  • Tax credits to individuals and businesses;
  • Building code mandates to achieve thermal insulation standards;
  • Building code mandates to achieve acoustical insulation standards; and
  • Subsidies and grants to manufacturers of certain insulation products.

Adverse consequences of insulation

Extremely efficient Tyvex wrap is increasingly common as a
skin insulation. Source:Scott Erhardt

The dark side of insulation arises from unintended consequences of achieving a tightly insulated structure. These adverse outcomes can include:

  • Increase in mortality from radon and other toxins;
  • Increase in illness, especially from respiratory disease;
  • Loss of worker productivity, from allergenic molds and other toxins; and
  • Increase in societal and individual costs for health care.

Causality of adverse impacts

There are several distinct mechanisms that produce adverse impacts of building toxin retention. They can be classifed as:

  • Insulation promoting increased concentration of radon gas;
  • Insulation promoting increased concentrations of chemical toxins;
  • Insulation promoting increased moisture accumulation leading to excessive molds; and
  • Insulation which contains intrinsically toxic materials.

Increased radon concentrations

Radon gas and its daughters are often attached to fine dust particles in the air—the main pathway of human exposure is inhalation. Radon is present in nearly all air. Background levels of radon in outdoor air are, however, generally quite low—about 0.003 to 2.6 picocuries of radon per liter of air. In indoor locations, levels of radon and daughters are often much higher than outdoor levels. Indoor radon levels are generally in the range of 1.5 picocuries radon per liter of air. Basement or foundation pores allow radon gas to migrate into a building from certain types of subsurface rocks. Additionally, many sources of interior stone finishes, such as certain granites, are outright sources of radon.

Efficient insulation of buildings frequently serve to elevate interior radon levels. Exposure to radon in building interiors is a leading source of death via lung cancer. In the USA, for example, the Environmental Protection Aagency estimates radon deaths at a level of 21,000 per annum, second only to tobacco smoking with respect to incidence of environmental or accidental mortality. Note that in developing countries, relative impacts of radon mortality are much less, since dwellings typically have a much higher air turnover rate, and the competing causes of lung cancer mortality (e.g. air pollution emissions from unscrubbed fossil fuelplants) are often much higher than in the Western countries. For example, official Chinese data show that about 400,000 people from year die from excess emissions of sulfur dioxide, oxides of nitrogen and other conventional air pollutants. The effects of radon mortality are distributed unevenly in a geographical sense, with much higher impact seen where underlying bedrock produces high radon emissions.

Interior buildup of chemical toxins

Aerosol sprays may not only use toxins to achieve a function,
but even canned air uses chemical propellants.

A variety of airborne chemical substances accumulate in building interiors; when highly efficient building skin insulation has occurred, these chemicals attain appreciably higher concentrations in the absence of aggressive mechanical ventilation. (Agressive mechanical ventilation, of course, defeats the purpose of elaborate insulation, since appreciable energy is used and by-product interior noise pollution is created). Prominent sources of the chemical toxins include tobacco smoke (nicotine, tar, radionuclides), carbon monoxide (from incomplete combustion of natural gas or heating oil), aerosol sprays (volatile organics, insecticides) and other household cleaning products. Second-hand smoke from tobacco smoke alone is estimated to contribute to tens of thousands of excess deaths per year worldwide, in addition to contributory factors of massive numbers of lung and heart disease illnesses.

Increased moisture accumulation

Interior condensation buildup in well insulated home, Ireland,
Source: Daniel Clauzier

There are a variety of common water vapor generating sources in the indoor environment, including showers and bathing, cooking and combustion of fossil fuels for space heating. In addition exhalation by people and pets and transpiration of indoor plants are sources of water vapor. When the building skin is tightly insulated, each of these vapor residues has a much longer residence time, unless aggressive mechanical ventilation is applied; however, the very use of intensive mechanical ventilation raises interior sound levels and mitigates against energy conservation by bringing in outside air and by the operating energy costs of the ventilation hardware.

For interior rooms that have one or more walls embedded underground, there are special problems of moisture accumulation. Generally the soil moisture content below one meter in depth is sufficient to drive an osmotic process, whereby exterior soil moisture invades the building space, even through masonry walls. Furthermore, it is very difficult to exhaust high accumulation of building air moisture in basement like settings, since the masonry is sufficiently impermeable, thus impeding significant exfiltration. One has, therefore, the worst of all worlds: slow exfiltration of interior air when there is an interior moisture source and steady infiltration of exterior soil moisture into the basement, when the interior air begins with a relatively dry content.

In any case, a tightly insulated building creates an environment where moisture levels are high, providing an ideal growth environment for thousands of types of molds and mildew. While most of these species are not inherently toxic, many are highly allergenic. These allergens and pathogens often are seen growing on wall, ceiling and floor surfaces; more insidiously, they may be propagating within the wall cavities or plenums and are almost always present as airborn micro-organisms.

In addition to adverse health impacts from such fungal growth in high moisture content buildings, there are widespread occurrences of destruction of the actual structures. This destruction includes wood rot to studs and joists, interior surface damage from mold growth and corrosion of metal studs in cases where moisture is entrapped between an impervious outer skin (e.g. Tyvex type coating) and impervious interior surface sealant. A related defect that is common for double paned glazing is the long term entrapment of moisture between the two panes, causing adverse aesthetic and visual impacts.

Use of intrinsically toxic materials as insulation

Worker sprays on insulation that is so toxic that
protective gear is required. Source: U.S.EPA

Historically, asbestos has been used for building insulation, due to its efficacy and fire retardant properties; Modern building materials, however, have been developed, some containing chemical substances and fibers that may present potentially greater carcinogenic and other toxic risks. Such chemical substances as methylene diphenyl diisocyanate and toluene diisocyanate are likely sources of such risks. While the USA and other Western countries are identifying these risks with some alacrity, many materials have been installed for insulation before adequate understanding of the total risk. Moreover, there are future risks from use of such substances in developing countries—where standards of public health protection have not reached the levels of Western countries.

A special case exists in the use of certain granites and other decorative stone for interior appointments. While such decorative stone is not meant to serve as an insulating medium, many of these materials have been found to emit levels of radon gas that present risks. These effects, of course, are accentuated when extensive building skin insulation is advanced where such materials exist. All decorative stone do not pose such risks, but building contractors do not routinely screen decorative stone, and most local building departments are not aware of this form of risk. These decorative stone elements are used often in residences—especially in kitchen and bathroom settings as well as for hearth and serving bar applications.

Balancing risks with benefits

Balancing the risks of human health impacts and building materials damage with the benefits of energy savings and sound level reduction is a challenging matter. Decisions made will depend largely on the microclimate, state of existing insulation efficacy and budget available for insulation. Methods of improving on achieving balance of risks versus benefits may consist of the following structural changes in insulation decision making:

  • Aggressive promulgation of information about health risks that may arise from building insulation to homeowners, commercial property owners, building managers and local building officials;
  • Elimination of federal involvement in insulation programs, in favor of state and local programs, where knowledge of local meteorology and radon risks may be known better;
  • Removal of certain arbitrary insulation requirements on building skins, that may not have been developed with comprehensive understanding of health risks; and
  • Pursuit of research into improved methods of insulation that may allow a prescribed amount of air exchange through the building skin, and that might avoid use of toxic materials.


  • William Clark. 1998. Retrofitting for energy conservation. McGraw Hill. ISBN 0-07-011920-1.
  • George Dubose, J.Odom and J. David Odom. 2000. Commissioning Buildings in Hot Humid Climates: Design & Construction Guidelines. CRC Press. 100 pages.
  • C.W.Heath, P.D.Bond, D.G.Hoel and C.B.Meinhold. 2004. Residential radon exposure and lung cancer risk: commentary on Cohen's county-based study. Health Phys 87 (6): 647.
  • S.Darby, D.Hill and R.Doll. 2005. Radon: a likely carcinogen at all exposures. Ann. Oncol. 12 (10): 1341.
  • J.D.Spengler, J.M.Samet and J.F.McCarthy. 2001. Indoor Air Quality Handbook. New York: McGraw–Hill. ISBN 0-07-445549-4.

Further Reading


C. Michael Hogan (2012) Dark side of insulation. ed. S. Draggan. Encyclopedia of Earth. National Council for Science and the Environment. Washington DC Retrieved from http://editors.eol.org/eoearth/wiki/Dark_side_of_insulation


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martin haley wrote: 05-16-2012 13:34:27

Hi, Very interesting and informative. I have a couple of observations though "The dark side of insulation arises from unintended consequences of achieving a tightly insulated structure". I believe the issues raised here are mainly valid but are largely to do with air tight construction rather than high levels of insulation. I appreciate the two often go hand in hand but the two are not intrinsically linked. The amount of vapour within a building depends on the relative production and ventilation rates. A warm surface (a consequence of insulation) is less likely to be subject to condensation and the associated risks of mould formation. Water vapour will condense on a poorly insulated non permeable surface easily where the surface temperature falls below due-point (e.g. the single glazed window in the picture). Tyvek as used for the outer skin in construction (shown in the picture) (e.g. Tyvek Supro) is considered as vapour permeable having a water vapour resistance of less than 0.25 MNsg–1. The idea is to have a impermeable inner surface and a highly permeable outer surface to prevent moisture from entering the fabric of the building and to allow any moisture within the fabric to escape easily to outside. This construction method reduces the chance of interstitial condensation and consequential mould growth within the fabric. With adequate ventilation (either natural e.g. passive stack or forced preferably via heat exchanger) the net effect of increased levels of insulation but not ventilation is to reduce energy consumption and associated emissions. Reducing both the ventilation and insulation will however increase the chance of condensation.


Faye Curtiz wrote: 12-27-2011 16:16:14

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